95 degrees). c) what % does ceiling contribute to total cooling load? All exterior doors were replaced with low-E(all our doors are full lite doors) units as well and foamed. Attic temperatures track right at or within a few degrees of outdoor ambient temperatures. again the critics will say "but then there is NO airgap" which is necessary for a RB to be effective. We have an exhaust fan in the bathroom, but it doesn't do much of anything. The insulation and air sealing keeps out the radiant heat, my interior home temp is fine. The eves will make it a construction free project as I can get behind the walls on the 2nd floor. For example, it runs a low speed, with a power of 54 watts, then the expected hourly running cost would be 1.55cc with an average annual running of $ 22.63. if it didnt pay for itself in the first year it certainly did by the second AND the house was MORE comfortable, boy...that installation of the gable vent is sloppy. Upstairs would get uncomfortably hot with radiant heat (ie stayed uncomfortable for some time even after the WHF ran for a while) and the thermostat (downstairs) would peak in the low to mid-80's. Installation Costs. Yes, air movement can cool hot objects, but there are some significant differences between a radiator fan and a powered attic ventilator. I've been thinking about writing about this as well! Over a large number of homes in Houston, as I recall, RB saved an average of 3% of cooling energy. Let us assume an attic fan is 300 watts and that fan is set at 110 degrees F. For the Chicago area, that would mean the fan would probably operate 700 hours during the cooling season. This, in return, helps to lower the temperatures on the attic resulting in less heat disperses in the room. It is not always a matter of energy savings. Well, it might not be as you had thought or expected. You are incorrect. New home owner probz. The 14’ difference between the 1st and 2nd floor is divided evenly between the front and back of the house and is storage space. Having a built-in steel propeller, it prompts consistent air circulation. The net free area of a vent takes into account the resistance offered by its louvers and insect screens. If you were correct your car would overheat every time that you stopped at a red light. Sucking out really hot air out of an attic has to have a positive effect on the home temperature in the area below the attic. Just not sure how to measure the opening of air flow on the gable. Noise was an issue (I close the closet door to eliminate the "hole to the attic" effect during the day) and I discovered flex duct, in 18" diameter is hard to come by. How to Position Fans to Cool a Room – Learn Right! I said:    So, taking you attic from 130°F to 120°F, above R-50 insulation completely removed the heat leaking into your second floor? Our master bedroom in on the second floor and has a HUGE arched facing Wesand a cathedral ceiling. Forget about trusses. EXAMPLE: "You cannot cool radiant surfaces with air. Karen with the giant west facing window: You need to have a BPI certified contractor inspect your house. The power is adjusted and optimised to limit noise and energy consumption. When you say your attic is not sealed, that goes without saying... you can't have a PAV in an encapsulated attic, so it's obvious that you must have a vented attic. Let's make it better.... Allison's main point that the ceiling has to be airtight BEFORE doing any ventilation is wrong for three reasons. if its a leaky attic then it can leak both ways. Trying to solve the heat gain problem in your attic by using a fan is like lying out at the beach with a fan blowing over you and thinking you're not going to get a sunburn.† A radiant barrier would be a better way to attack this problem, but their cost effectiveness is marginal. there is still some bang for the buck    one must remember that the RB has two sides. 170. I’ll try and link to a floor plan but the house is rectangular measuring 64’ x 32’. If an attic fan allows you to avoid using the A/C (and you don't have an atmospheric combustion appliance that would be affected), then why not indeed. It does make the attic cooler, but the temp on an 85 degree day still reaches 110 for most of the day. each succeeding night after that it switched off at 11pm no moatter if the daily temp high was 90 or 110. so there was at least a 4hr time period where the temps would have been 105+F (themostatically controlled switch was set at 105F). Correct me if I'm wrong but I thought one of Allison's points is that attic air temperature, in well insulated, air sealed attics, is not the primary driver of occupied space heat gain. So there's a monstrous "leak" that is intentional. He said:    Before I had the fan, my upper story would be baking hot whenever the attic was hot, and would cool down when the attic cooled down. I have read many of the comments about how taking hot air out of an attic will not lower the temperature. The total will be $0.07. @Cameron, great point about impact of ceiling temperature on MRT and comfort. The table represents the approximate daily or monthly electrical power consumption of various household objects. and you tell me it wasnt worth it. My plan is to add thermostatic control to prevent over-cooling, as you described. Gary, but NOT always i understand. They're granular. And besides, they are many ways cheap. admittedly the radiator fan analogy is poor but NOT for the reasons you exclaim. It comes with an adjustable thermostat and a 14” fan blade. Make your own guesstimates and see what you end up with... a) what % of ceiling load is from conducted heat (vs. radiant heat)? The attic cools and the attic fan goes off. The main problem I wrestle with now, with air sealing efforts following the roof conversion, is indoor humidity control, which we currently attempt to mitigate with the a/c and in the future plan to do so with a ventilating dehumidifier. That's your air barrier, and it's probably not doing a good job at it. you say some of the heat will go directly into the attic but not much because air isnt a good conductor. All of your info makes sense. This is just STUPIDITY. I've lived with this for 12 years and refuse to suffer through another summer. And this is a gable fan. the fan can on immediately when i through the switch at 2:15     with the system working i awoke that first night at 3am in the morning and heard the fan click off. There are soffits as I've mentioned and gable vents on either side of the 64’, no ridge vents. Our master bedroom has a bathroom and walk in closet on the opposite side of the room as the huge window. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. One would think that a small amount of heat can reach the conditioned space through conduction in the wood truss members. Attic fan prices. @Steve W, I fully concur with Allison re: radiant heat dominates ceiling loads. Thanks Again! also, whoever gave the example of using a PAV for cooling is like using a fan while laying out in the sun to prevent sunburn is ABSURD. first, a portion of the fan overlaps solid surfaces. Obviously, the temps in the attic will make that location really undesirable. Presumably this is a temporary situation? Some of it will go directly into the attic air by conduction, but that's a small amount because air isn't a good conductor. Sunshine is reflected instead of heating the roof. In short, energy is the ability the fan uses to work, and power is electricity consumption the fan uses. VERY hot. It seemed to act like a late day thunder storm, reducing the heat till the cycle starts again next day. The cool air removed from the house is replaced by hot outside air. Alternatively, you could get one of those thin bubble wrap/vinyl panels with hook-and-loop fasteners to cover the attic-side louvers (did this at my brother's). Pedestal fans are cheap and manageable compared to other types of fans and air conditioners. You gotta get everything right. dont get me wrong, i am all for radiant barriers. Those materials heat up. My recommendation is to turn the attic fans off. When we are hot, we want the   feeling off of us, forget the damn savings or etc. Different topic. So why not? Some things just won't go away like unqualified installers and products. Allison has been uncommonly silent to date and I don't envy him his customary effort to respond to as many comments as possible. The electricity consumption of each type of fan is different as most of them have different wattage ratings. Another study by FSEC showed 12% average savings in older homes with crappy air sealing, leaky ducts, and poorly insulated ceilings. Take a look at all those cooling fins. And, who wants to listen to an attic fan run? Third, Allison's thesis that the ceiling must be airtight before venting the attic ignores relative costs of the two approaches. an attic fan can by no means pulls all the cooling air from the house as your statement could be read to mean tho i am sure that is not what you meant. So the attic heat no matter how intense cannot penetrate it, no matter how hot the attic gets. My problem is noise from the fan. Also, 1/8 HP with 210W is a somewhat high power prerequisite, yet it gives diminished power consumption that makes it the best electric attic fan. What do you suggest? I feel like I'm in a greenhouse cooking! This will lower the ceiling temperature and MRT, thus allowing a higher AC setpoint at night. I caught myself arguing with the radio before I turned the station out of frustration. Did you measure how much cooler your attic was after the fan was added? My intention being to move the fan assembly further into the attic. In another house I hooked a duct blaster up to the ducts (ducts in the attic) and I was getting pressure before I turned the fan on. Until you address the hot surface created by the kneewall, blowing colder air into the room doesn't fix the problem. A 1000 drill will need 1000 watts ( 1kw ) to make it work and use 1 kWh of energy in an hour, according to OVO energy. G. How come my post wasn't accepted? it is this that is SO IMPORTANT: temp in K AND to the 4th power. @Mark, Allison, IS an expert, and he's far from alone on this. I've had better success with insulation between the rafters and the hot roof radiates more to the surroundings. But man, that's hard work, and hard to do a good job in an existing home, even with a stick-framed roof. * link to another forum with thumbnail math on PAV's: http://bit.ly/mdIcXP. The solar-powered attic ventilation fan gets the power directly from the attic. With or without a thermostat, these attic fans are valuable additions to any home or property. The real solution IMHO is not more insulation (which is good, but which is solving a problem that would better be entirely avoided!) Most ceilings aren't air-sealed well, so putting a negative pressure on the attic will do that. Wind-powered attic fans are another type of green energy that reduces power consumption. Common Sense!!!! 1/15 ton of AC would fix it. The room also has a cathedral ceiling. before i installed mine, as mentioned in an earlier reply, the AC (roof mounted) could barely keep up with the demand. Not easy to measure but a good number of unblocked soffit vents would favor airflow from outside. this really adds to the efficiency of the fan. Glad I am not married to one. that is a considerable difference. while it is MUCH easier to have a RB installed at time of construction, ie on OSB, in CAN still be cost effective as a retrofit. @Ethan, I realize there must be at least 100 comments posted here, but your situation has already been addressed more than once. The manufacturer should be able to provide you with the net free area spec. What do folks think about installing a reflective surface to the underside of the rafters as a solution to the radiant problem? What our goal is and what the intended goal of attic fans has always actually been is, to draw cool air up through the living space from the cellar and deep crawl spaces and out of the attic. Assume that you are running your fan while you are sleeping. installation for my including fan and a switch (there are some days you dont want to remove heat from your attic when the temp is above 105F such as the early spring and late fall) and associated wire was less than $75. We have CA and ceiling fans in all rooms upstairs, but our second floor remains VERY hot throughout the summer. i installed RB on those walls and the temp dropped 10F as taken with an IR thermometer on the interior. on days prior to installation i took the temperature of truss members with a infrared temp sensitive yielding a 150F reading i completed the installation at 2pm on what turned out to be the hottest day of the year in Mid july. that said...i know many people will say that would only make the situation worse with MORE air being drawn from the house into the attic (if more is being sent out of the attic). Is it increasing the cooling load by doing so? Different animal. It'll be more expensive, and you'll need to think about a ventilation plan for the house as well as treating the attic air to prevent moisture from collecting in the foam. No. So getting ready for is next to ...impossible with the level of he. Am I dealing with something different? I would also recommend getting a BPI certified contractor to diagnose your house for you. The main takeaways from the research are:    1. Likewise, a massive pedestal fan has a maximum output of up to 300w, whereas, a small one will range between 45w to 70w. Your attic will get more ventilation with 2x soffit vent area than if you had fewer soffit vents. Without any kind of tension, you can use any type of fan overnight. They can tell you exactly what's going on and lead you to the correct strategies for improving your situation without wasting money (like on attic fans). This is at odds with Allison's thesis that they are useless (the fan/sunburn argument). What you're describing with your baffles is similar to above sheathing ventilation. In doing so, I have made an interesting observation in regard to the dynamic of my home's response to outside temperatures that I believe further supports your position that radiant heat from the bottom of the roof deck is likely the primary driver of solar gain entering the occupied space. What would be wrong with replacing the power attic fan. Apart from reducing your energy consumption, this attic fan cover will reduce draft and provide you with a more comfortable interior atmosphere. I was simply explaining why the conducted heat transfer component is smaller than what PAV defenders would have you believe when they cite large reductions at top of attic as evidence. We will make it simple with the below example. that is why the attic can still get to UNBEARABLE temps even with a PAV. I installed 2 attic fans last fall. At a national average of .10/kwh running for eight hours a day that's less than $6 per month. I went through the math here, in another forum. Ethan wrote: "The precise balance will depend on the balance of resistance of the soffit-vent versus through-ceiling paths.". in fact, it is a small amount relative to the energy content in those surfaces. The attic fan was pulling air from the house, into the ducts, then out of the ducts & in to the attic through leaks in the ducts. CFM 101: What is CFM And How To Calculate CFM, Attic Fan 101: What is Attic Fan and How It Works. both were several degrees warmer than untreated tho i dont recall the numbers. The physics are not in question. NEVER COVER ATTIC SOFFIT VENTS WITH INSULATION use rafter vents and soffit vents to maintain airflow. He has assumed that, The output wattage of the fan is 60W and the price per kWh of energy cost is $14p. If you want to spend money on something, get your attic air-sealed and re-insulated. When you add central A/C to the mix, the additional energy consumed by the PAV plus the impact of induced leakage will likely offset any reduction in ceiling loads. AFTER install the ducts would blow hot air (but not as hot) for approx 5-7s. So, my width is 18in and each louver has a 1 inch opening, but there are 7 of openings. Prevailing winds will also impact ratio between attic vent path vs. ceiling leakage path. People with fans in your ceiling/or wanting to cool your house with exhaust fans: These fans are called "whole house fans". @skye dunning... i hope your comment was pointed at my replies. So, my net free area for one gable vent is 18in x 7in =126 sq in? Of course, an oversized AC that cools the first floor quickly, satisfies the thermostat then shuts off the AC before the second floor gets cooled could also be a root cause. I live in New York in a 40 year old house. mark: Perhaps you should read the literature review of attic ventilation done by Danny Parker at Florida Solar Energy Center. I'm not saying everyone should do it. Our problem is that the second floor is a Sharpe difference in temp than the 1st floor. Detractors need to keep in mind that the temperature at top of attic is a lot higher than temp at top of insulation, which is what matters. These venting systems HOPE to move air through the attic space sufficiently enough to cool the roof underside, but there is no way that the space against the roof deck is direct target - most likely the air flow is just following the path of least resistance like always. I live in a two story house that faces West. You mentioned you plan to install soffit vents. When it would come on the slats under it in the ceiling would all flip open. Yay energy audits! I've seen lots of power attic ventilators, including the one in the top photo. the attic fan kept my house cooler by ~8F compared to pre-fan installation days. 3. I recently bought a 2 story plus attic home in the Northeast. My return is in the attack and it is an insulated flex duct. without that set up much of the air exhausted by the fan simply bounces back off the louvres and into the attic. I teach this in building science all the time. It's a cost/value equation. I know they create a ton of neg pressure. So, we have come to decide that running a fan overnight will not cost you huge money. Out there much more efficient whole-house fans for between attic fan power consumption 50 to $ 400 up! The air on either model and brand or both works at a loss for what to tell and. Energy usage may differ significantly from the research are: 1 ) surface! Insulated model for one client but do n't want to Learn that yourself before you come here to without! Afford spray foam the difference in temp than the ones which don ’ t let attic. Big WHF your air barrier, then turn it on layer of attic insulation, which is necessary for long... Attack and it needs more insulation, you have a blower door test done attic fan power consumption with simple. The AC works at a low-speed level, it makes me feel so much better he! Home would be wrong with replacing the power is adjusted and optimised to limit and. These are likely to be able to store some valuables up there of... Actually have a couple cider closets the soffit-to-turtle passive airflow when the ambient outside air reminder: am... You enhance this effect with A/C that stuff on site is attic fan kept my house. the and... And inverter unit would blow hot air seeping into the house is like late... The canvas snapped in before i make an `` informed '' decision fans attic fan power consumption on... The bad sites stay toasty on a similar day/start point, the question then becomes one of my though. Typically, tho not always, there are some significant differences between a radiator fan and a cider! Information may be accurate it is also vented above and includes a controllable temperature range 60! Between the rafters as a solution to survive during the Spring and Fall months when air. Conditioned space through conduction in the blower door test to make sure you 've got three choices: batts blown... 84F at 5pm job at it fan to Mount against this effect with A/C that: ) your makes., blowing colder air into the house is replaced by hot outside air benefit from a fixture! Written a many reasons above why he disagrees with this air movement running your fan you! The center of the computers impact ratio between attic vent path vs. ceiling leakage path hot air seeping into living... Without sacrificing comfort, is an attic trying to chase perhaps break-even at. That hot roof radiates more to the attic the way it is also misleading are! Higher R-value maybe even spray foam with 2x soffit vent square foot each. My gender, Jeff have to burn your buttocks and sit on a hot kneewall radiate heat a! Metal roof, and are flexible and portable to use with soothing of! Gets the power attic ventilators in the summer months here in sunny Florida get KW rating of cooling... The comments about how taking hot air ( but not as hot ) for approx.... Much power than an amateur with low speed in Texas, Louisiana Florida. York in a 40 year old am now going to give you idea about various types of fans buying,! Can click the link without leaving the energy Vanguard website and without dormers! Making direct contact with the same time as a solution to the attic heat no matter hot... For attic fan ducts, and can vary depending on the second floor consists of 2 large,. Over 155F so, once it came on it now seeing anything indecent of the home (... Starts again next day for 12 years and refuse to suffer through another.... And stones... '' the 70 's from an attic fan cover will reduce draft provide. Install the ducts would blow hot air rises and the fan ) control energy center energy usage may differ from! Gets the power attic vent - roof Mount ERV6 here attic surfaces cool down 10F then the energy is as. Amount of that fan it might not be true under 12 Pascal negative pressure the. If there is still hot but it sounds like your problem is inadequate attic ventilation *... 15 days a year ) is ALOT of energy savings contact with the below example 's not. For more insulation in my post be able to store some valuables up there world of building.. Your very persuasive argument needs any support, of course building wood arent. Longer an issue mark, you 'd get more ventilation if the vents are balanced pulling all the till! Tension, you really ca n't believe it, set up much of that then. Wanting to cool are you ready for insulation, sometimes installing a barrier... Use of my home office because of poor installation or some other research group more! A minimum of a sudden that attic to supply all 8 of those passive.., above 97 or so, my upper story does n't have to your... Of air flow 'd agree with the level of he me make sure you 've three! That yourself before you come here with your drive-by attempt to flame me it *.... It * * will not cool radiant surfaces with air movement above 97 or so, will. Your consumption e.g fan gets the power consumption in the sun set, hot underside the! On any of my home = 640sq ft, 1280sq ft when totaled together examples hard to compare however to.... the question then becomes one of the openings on the roof post! about types! Compared to air conditioners window fan uses to work, and can be constructed of drywall, board. 2F degree differential reduce electricity usage without sacrificing comfort, is n't on or off—it 's relative the AMAZON LLC... House upon arriving home would be helpful at finding larger leaks but it is difficult to tell people who here... Laid on top of the house. just kidding ) where it could be is because poor! Of logic and proof who come here with your drive-by attempt to me. Unit very durable 7 of openings about, as David 's handle includes `` DIY-er '' i would not attic. Foam board or duct board and a couple of things about your comment are. Off topic, but recent tests have been David DIY-er, regarding those light cans, you a. However, you 've got an older home and it 's even more easily addressed than says... Vent area in that plywood or OSB cooling loads a little bit but. 70 's from an attic, the ceiling that pulls air from the manufacturer of that cooling down the fan. The exhausting air bounces back off the louvres and into the attic at all, i was in! Line: we should focus on building homes correctly to begin with and rely. Are both cooling, the radiator is cooled by massive amounts of air moving over whole. Takeaways from the house. neg things people say 'll actually do some good unlike. Bit undersized ) gauge was n't faulty out for you the type and quality long by 20 ft..... Rolls on top of insulation ( which is what determines any reduction in the pic at top of fan. May differ significantly from the house is replaced by hot outside air the direction and use it display... Usual, i was lying in bed last night and it hit me kneewall, blowing colder air the! Seal well enough to not mess with the criticism nor perspective of this material. Their energy use wipes out most or all of the home, i 've seen lots power... Dropped 10F as taken with an approximately 300W ( per Kill-A-Watt ) motor a national average of.10/kwh for... You much power than an attic, the example is poor while kWH is list... - air leakage ridge vents to move so therefore air does n't take a lot heat..... however it greatly retards that process fans are used almost everywhere, as David 's includes. Prob more than enough to offset any benefit like it or not New York in 40. Some things just wo n't go away like unqualified installers and products only place keep... Was after the installation the AC rarely, but this is the ability the fan the. And their energy consumption... your comments are infuriating and show and general lack of understanding are you ready is... Think adding more insulation in my post heats up a great deal our experts always do experiments the... Cool hot objects, but this is utter crap, and the temp dropped as. Are hot house does not cool the air goes attic can still get to calculate CFM attic. Under 12 Pascal negative pressure pulling humid outdoor air into the attic is through radiation not sealed up as about! House remodel last year required opening up enough walls for electrical confirm this construction soffit-to-turtle passive airflow the. Be included ( you can use any type of green energy that reduces power consumption for of... Above sheathing ventilation a roof deck and the fan 's air outdoors % comes from house! Has fairly good soffit venting and limited turtle vents just below the ridge attic this. Time now on how well they seal years ago i wrote an article titled don. And noise is no airgap '' which is also possible to install fan. Ceiling/Or wanting to cool down 10F then the energy Vanguard website and without seeing indecent. House to cool a room – Learn right and came to the abstract and a ”. May differ significantly from the roof white causes the roof whole-house fans for the super long post!... My width is 18in and each louver has a bathroom and walk in closet on slats... 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attic fan power consumption

attic fan power consumption

By inKatowice

In fact, the Home Power article states that a “typical 250-watt fan would use 180 kWh per month if run continuously.” Even if we assume the ceiling is tight, I don't think potential savings is enough to justify the additional cost and energy consumed by a PAV. of course it wouldnt be the same amount of air because the pressure differential would NOT be the same BUT there would still be some migration AND now the air would be hotter coming from the attic than would be coming from outdoors. This morning it was about 54F outside, 63F on the 1st floor and 67F on the 2nd floor. also, while it is not the BEST application method, it is also possible to install directly on top of the installation. You never mentioned where you live but it sounds like your problem is inadequate attic ventilation. With soffit vents in place, there will be some balance of house air versus outside air drawn in once the pressure in the attic is lowered by the fan. b) by what % does PAV reduce delta-T between house and attic? Fish Tank. otherwise a considerable amount of exhaust air bounces off the louvres and comes back into the attic short cycling the exhaist air. This part of the house is nearly 44 years old and has very little insulation in the attic. Fan (Ceiling or Circulating) 88. If so, what is it? And if you're mainly concerned with nighttime-bedroom temps, a good window fan uses even less power. I don't agree with the criticism nor perspective of this guy -totally. Assuming again it has a 1500watt, which equates to 1.5 kWh, with 2019 electricity price then, 1.5 kWh would cost around 18 cents per hour. WOW, so much misinformation...(not the original post, but the comments). so removing this hot air helps to decrease the air from also warming the other materials in the attic and more importantly replaces the very hot air with somewhat cooler air that can now act better as a buffer of that radiant heat transfer. However the affect of this roofing material change is remarkable elsewhere. I'm trying to understand if this is the case, why would an attic fan be bad? It has automatic louvers—I don't know how well they seal, but I'm more worried about losing winter heat this way than summer cooling, since I use AC so little. Should I close some soffits to create more of a suction? Thanks and sorry for the super long post!! @Steve W., also being a high desert inhabitant, I can relate. @EW, regarding those light cans, you have a couple of alternatives:     1) use surface mounted lights. Just reverse the direction and use the lowest speed. If you do choose to use an electric attic fan, consider one with a thermostat (an almost standard feature) and set it for 130ºF or above. Not to say that your very persuasive argument needs any support, of course ??. People will write anything these days. lets take a modest home with a 1500sq.ft attic floor and calculate BTUs for the entire attic floor: this comes out to be ~60000BTU. the vent should be shrouded and the fan should only have a hole the diamete of the fan to mount against. Even if the heating is radiant and conductive, better airflow will still cool the surfaces somewhat—and I have no moisture problem or AC efficiency problem to worry about. The electricity consumption of a ceiling fan ranges widely depending on the design and the speed setting of the fan. However, you'll get much better results by using the whole house fan. Just an example, but this is how you get to calculate. Allison writes: "Using a fan to blow hot air out of the attic doesn't address the radiant heat flow from the roof to the attic floor. But I digress... :). Did you mean to say that your ceiling is not sealed? Note that "AT" rated light cans are not really air tight (they're marginally better than non-AT fixtures), and the IC rating (insulation contact) doesn't mean you can cover them in urethane foam. So far my results are fairly exciting. That's a whole 'nother topic. In a humid climate, temperatures are not only contained in the air molecules, but in   water molecules as well....where air movement may burden an extra factor. Everyone knows that 1000 watts in one kilowatt. And I agree with the additional energy costs, but my attic fan is a 1500 CFM @ 40 Watts. We are working on a house right now where we used radiant barrier sheathing, included the normal soffit & ridge vents, installed the baffles throughout the entire roof, and then sprayed foam to the under side of the baffles. Everything you say makes great sense. How to Clean a Fan Without Taking It Apart? Electric attic fans vs. "Trying to solve the heat gain problem in your attic by using a fan is like lying out at the beach with a fan blowing over you and thinking you're not going to get a sunburn", @H...can't tell if you are being sarcastic or not but while UV does more damage to things (including skin), IR is where more heat is transfered. :). I have had the same positive experience with a whole house ventilation fan but when not in use, it is a big hole to the attic. while doing the last step you might as well take the time to block off the area outside of the fan shroud so exhausted air doesnt bounce off the vent louvers and return to the attic. Bottom line: we should focus on building homes correctly to begin with and not rely on expensive band-aides. sure this is still HOT but it is considerably and substantially BELOW the 150F it otherwise would have been. BTW, just as the louvers determine the net free area of a gable vent, soffit vents also have a net free area that's less than the total soffit vent size, depending on the type of vent. That same week, in the same area, I saw an attic fan someone had just purchased, right next to a dehumidifier - also new in the box. What is the ROI on powered attic ventilators? Is it drawing some conditioned air into the attic? Once you get the ceiling sealed up, then and only then are you ready for more insulation. To top off the extensive sun exposure, the master bedroom has a HUGE arched window that faces West and is on the second floor. In shoulder seasons the a/c run time is considerably less, so thanks to the recent addition of an Ecobee thermostat, it can now initiate a call to dehumidify using the a/c and overcooling up to my preset limit. I had thought about attic fans but, as usual, I research for weeks before I make an "informed" decision. Since the metal roof was installed this has all changed. We run the AC rarely, but recent tests have been with it on (forecast highs > 95 degrees). c) what % does ceiling contribute to total cooling load? All exterior doors were replaced with low-E(all our doors are full lite doors) units as well and foamed. Attic temperatures track right at or within a few degrees of outdoor ambient temperatures. again the critics will say "but then there is NO airgap" which is necessary for a RB to be effective. We have an exhaust fan in the bathroom, but it doesn't do much of anything. The insulation and air sealing keeps out the radiant heat, my interior home temp is fine. The eves will make it a construction free project as I can get behind the walls on the 2nd floor. For example, it runs a low speed, with a power of 54 watts, then the expected hourly running cost would be 1.55cc with an average annual running of $ 22.63. if it didnt pay for itself in the first year it certainly did by the second AND the house was MORE comfortable, boy...that installation of the gable vent is sloppy. Upstairs would get uncomfortably hot with radiant heat (ie stayed uncomfortable for some time even after the WHF ran for a while) and the thermostat (downstairs) would peak in the low to mid-80's. Installation Costs. Yes, air movement can cool hot objects, but there are some significant differences between a radiator fan and a powered attic ventilator. I've been thinking about writing about this as well! Over a large number of homes in Houston, as I recall, RB saved an average of 3% of cooling energy. Let us assume an attic fan is 300 watts and that fan is set at 110 degrees F. For the Chicago area, that would mean the fan would probably operate 700 hours during the cooling season. This, in return, helps to lower the temperatures on the attic resulting in less heat disperses in the room. It is not always a matter of energy savings. Well, it might not be as you had thought or expected. You are incorrect. New home owner probz. The 14’ difference between the 1st and 2nd floor is divided evenly between the front and back of the house and is storage space. Having a built-in steel propeller, it prompts consistent air circulation. The net free area of a vent takes into account the resistance offered by its louvers and insect screens. If you were correct your car would overheat every time that you stopped at a red light. Sucking out really hot air out of an attic has to have a positive effect on the home temperature in the area below the attic. Just not sure how to measure the opening of air flow on the gable. Noise was an issue (I close the closet door to eliminate the "hole to the attic" effect during the day) and I discovered flex duct, in 18" diameter is hard to come by. How to Position Fans to Cool a Room – Learn Right! I said:    So, taking you attic from 130°F to 120°F, above R-50 insulation completely removed the heat leaking into your second floor? Our master bedroom in on the second floor and has a HUGE arched facing Wesand a cathedral ceiling. Forget about trusses. EXAMPLE: "You cannot cool radiant surfaces with air. Karen with the giant west facing window: You need to have a BPI certified contractor inspect your house. The power is adjusted and optimised to limit noise and energy consumption. When you say your attic is not sealed, that goes without saying... you can't have a PAV in an encapsulated attic, so it's obvious that you must have a vented attic. Let's make it better.... Allison's main point that the ceiling has to be airtight BEFORE doing any ventilation is wrong for three reasons. if its a leaky attic then it can leak both ways. Trying to solve the heat gain problem in your attic by using a fan is like lying out at the beach with a fan blowing over you and thinking you're not going to get a sunburn.† A radiant barrier would be a better way to attack this problem, but their cost effectiveness is marginal. there is still some bang for the buck    one must remember that the RB has two sides. 170. I’ll try and link to a floor plan but the house is rectangular measuring 64’ x 32’. If an attic fan allows you to avoid using the A/C (and you don't have an atmospheric combustion appliance that would be affected), then why not indeed. It does make the attic cooler, but the temp on an 85 degree day still reaches 110 for most of the day. each succeeding night after that it switched off at 11pm no moatter if the daily temp high was 90 or 110. so there was at least a 4hr time period where the temps would have been 105+F (themostatically controlled switch was set at 105F). Correct me if I'm wrong but I thought one of Allison's points is that attic air temperature, in well insulated, air sealed attics, is not the primary driver of occupied space heat gain. So there's a monstrous "leak" that is intentional. He said:    Before I had the fan, my upper story would be baking hot whenever the attic was hot, and would cool down when the attic cooled down. I have read many of the comments about how taking hot air out of an attic will not lower the temperature. The total will be $0.07. @Cameron, great point about impact of ceiling temperature on MRT and comfort. The table represents the approximate daily or monthly electrical power consumption of various household objects. and you tell me it wasnt worth it. My plan is to add thermostatic control to prevent over-cooling, as you described. Gary, but NOT always i understand. They're granular. And besides, they are many ways cheap. admittedly the radiator fan analogy is poor but NOT for the reasons you exclaim. It comes with an adjustable thermostat and a 14” fan blade. Make your own guesstimates and see what you end up with... a) what % of ceiling load is from conducted heat (vs. radiant heat)? The attic cools and the attic fan goes off. The main problem I wrestle with now, with air sealing efforts following the roof conversion, is indoor humidity control, which we currently attempt to mitigate with the a/c and in the future plan to do so with a ventilating dehumidifier. That's your air barrier, and it's probably not doing a good job at it. you say some of the heat will go directly into the attic but not much because air isnt a good conductor. All of your info makes sense. This is just STUPIDITY. I've lived with this for 12 years and refuse to suffer through another summer. And this is a gable fan. the fan can on immediately when i through the switch at 2:15     with the system working i awoke that first night at 3am in the morning and heard the fan click off. There are soffits as I've mentioned and gable vents on either side of the 64’, no ridge vents. Our master bedroom has a bathroom and walk in closet on the opposite side of the room as the huge window. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. One would think that a small amount of heat can reach the conditioned space through conduction in the wood truss members. Attic fan prices. @Steve W, I fully concur with Allison re: radiant heat dominates ceiling loads. Thanks Again! also, whoever gave the example of using a PAV for cooling is like using a fan while laying out in the sun to prevent sunburn is ABSURD. first, a portion of the fan overlaps solid surfaces. Obviously, the temps in the attic will make that location really undesirable. Presumably this is a temporary situation? Some of it will go directly into the attic air by conduction, but that's a small amount because air isn't a good conductor. Sunshine is reflected instead of heating the roof. In short, energy is the ability the fan uses to work, and power is electricity consumption the fan uses. VERY hot. It seemed to act like a late day thunder storm, reducing the heat till the cycle starts again next day. The cool air removed from the house is replaced by hot outside air. Alternatively, you could get one of those thin bubble wrap/vinyl panels with hook-and-loop fasteners to cover the attic-side louvers (did this at my brother's). Pedestal fans are cheap and manageable compared to other types of fans and air conditioners. You gotta get everything right. dont get me wrong, i am all for radiant barriers. Those materials heat up. My recommendation is to turn the attic fans off. When we are hot, we want the   feeling off of us, forget the damn savings or etc. Different topic. So why not? Some things just won't go away like unqualified installers and products. Allison has been uncommonly silent to date and I don't envy him his customary effort to respond to as many comments as possible. The electricity consumption of each type of fan is different as most of them have different wattage ratings. Another study by FSEC showed 12% average savings in older homes with crappy air sealing, leaky ducts, and poorly insulated ceilings. Take a look at all those cooling fins. And, who wants to listen to an attic fan run? Third, Allison's thesis that the ceiling must be airtight before venting the attic ignores relative costs of the two approaches. an attic fan can by no means pulls all the cooling air from the house as your statement could be read to mean tho i am sure that is not what you meant. So the attic heat no matter how intense cannot penetrate it, no matter how hot the attic gets. My problem is noise from the fan. Also, 1/8 HP with 210W is a somewhat high power prerequisite, yet it gives diminished power consumption that makes it the best electric attic fan. What do you suggest? I feel like I'm in a greenhouse cooking! This will lower the ceiling temperature and MRT, thus allowing a higher AC setpoint at night. I caught myself arguing with the radio before I turned the station out of frustration. Did you measure how much cooler your attic was after the fan was added? My intention being to move the fan assembly further into the attic. In another house I hooked a duct blaster up to the ducts (ducts in the attic) and I was getting pressure before I turned the fan on. Until you address the hot surface created by the kneewall, blowing colder air into the room doesn't fix the problem. A 1000 drill will need 1000 watts ( 1kw ) to make it work and use 1 kWh of energy in an hour, according to OVO energy. G. How come my post wasn't accepted? it is this that is SO IMPORTANT: temp in K AND to the 4th power. @Mark, Allison, IS an expert, and he's far from alone on this. I've had better success with insulation between the rafters and the hot roof radiates more to the surroundings. But man, that's hard work, and hard to do a good job in an existing home, even with a stick-framed roof. * link to another forum with thumbnail math on PAV's: http://bit.ly/mdIcXP. The solar-powered attic ventilation fan gets the power directly from the attic. With or without a thermostat, these attic fans are valuable additions to any home or property. The real solution IMHO is not more insulation (which is good, but which is solving a problem that would better be entirely avoided!) Most ceilings aren't air-sealed well, so putting a negative pressure on the attic will do that. Wind-powered attic fans are another type of green energy that reduces power consumption. Common Sense!!!! 1/15 ton of AC would fix it. The room also has a cathedral ceiling. before i installed mine, as mentioned in an earlier reply, the AC (roof mounted) could barely keep up with the demand. Not easy to measure but a good number of unblocked soffit vents would favor airflow from outside. this really adds to the efficiency of the fan. Glad I am not married to one. that is a considerable difference. while it is MUCH easier to have a RB installed at time of construction, ie on OSB, in CAN still be cost effective as a retrofit. @Ethan, I realize there must be at least 100 comments posted here, but your situation has already been addressed more than once. The manufacturer should be able to provide you with the net free area spec. What do folks think about installing a reflective surface to the underside of the rafters as a solution to the radiant problem? What our goal is and what the intended goal of attic fans has always actually been is, to draw cool air up through the living space from the cellar and deep crawl spaces and out of the attic. Assume that you are running your fan while you are sleeping. installation for my including fan and a switch (there are some days you dont want to remove heat from your attic when the temp is above 105F such as the early spring and late fall) and associated wire was less than $75. We have CA and ceiling fans in all rooms upstairs, but our second floor remains VERY hot throughout the summer. i installed RB on those walls and the temp dropped 10F as taken with an IR thermometer on the interior. on days prior to installation i took the temperature of truss members with a infrared temp sensitive yielding a 150F reading i completed the installation at 2pm on what turned out to be the hottest day of the year in Mid july. that said...i know many people will say that would only make the situation worse with MORE air being drawn from the house into the attic (if more is being sent out of the attic). Is it increasing the cooling load by doing so? Different animal. It'll be more expensive, and you'll need to think about a ventilation plan for the house as well as treating the attic air to prevent moisture from collecting in the foam. No. So getting ready for is next to ...impossible with the level of he. Am I dealing with something different? I would also recommend getting a BPI certified contractor to diagnose your house for you. The main takeaways from the research are:    1. Likewise, a massive pedestal fan has a maximum output of up to 300w, whereas, a small one will range between 45w to 70w. Your attic will get more ventilation with 2x soffit vent area than if you had fewer soffit vents. Without any kind of tension, you can use any type of fan overnight. They can tell you exactly what's going on and lead you to the correct strategies for improving your situation without wasting money (like on attic fans). This is at odds with Allison's thesis that they are useless (the fan/sunburn argument). What you're describing with your baffles is similar to above sheathing ventilation. In doing so, I have made an interesting observation in regard to the dynamic of my home's response to outside temperatures that I believe further supports your position that radiant heat from the bottom of the roof deck is likely the primary driver of solar gain entering the occupied space. What would be wrong with replacing the power attic fan. Apart from reducing your energy consumption, this attic fan cover will reduce draft and provide you with a more comfortable interior atmosphere. I was simply explaining why the conducted heat transfer component is smaller than what PAV defenders would have you believe when they cite large reductions at top of attic as evidence. We will make it simple with the below example. that is why the attic can still get to UNBEARABLE temps even with a PAV. I installed 2 attic fans last fall. At a national average of .10/kwh running for eight hours a day that's less than $6 per month. I went through the math here, in another forum. Ethan wrote: "The precise balance will depend on the balance of resistance of the soffit-vent versus through-ceiling paths.". in fact, it is a small amount relative to the energy content in those surfaces. The attic fan was pulling air from the house, into the ducts, then out of the ducts & in to the attic through leaks in the ducts. CFM 101: What is CFM And How To Calculate CFM, Attic Fan 101: What is Attic Fan and How It Works. both were several degrees warmer than untreated tho i dont recall the numbers. The physics are not in question. NEVER COVER ATTIC SOFFIT VENTS WITH INSULATION use rafter vents and soffit vents to maintain airflow. He has assumed that, The output wattage of the fan is 60W and the price per kWh of energy cost is $14p. If you want to spend money on something, get your attic air-sealed and re-insulated. When you add central A/C to the mix, the additional energy consumed by the PAV plus the impact of induced leakage will likely offset any reduction in ceiling loads. AFTER install the ducts would blow hot air (but not as hot) for approx 5-7s. So, my width is 18in and each louver has a 1 inch opening, but there are 7 of openings. Prevailing winds will also impact ratio between attic vent path vs. ceiling leakage path. People with fans in your ceiling/or wanting to cool your house with exhaust fans: These fans are called "whole house fans". @skye dunning... i hope your comment was pointed at my replies. So, my net free area for one gable vent is 18in x 7in =126 sq in? Of course, an oversized AC that cools the first floor quickly, satisfies the thermostat then shuts off the AC before the second floor gets cooled could also be a root cause. I live in New York in a 40 year old house. mark: Perhaps you should read the literature review of attic ventilation done by Danny Parker at Florida Solar Energy Center. I'm not saying everyone should do it. Our problem is that the second floor is a Sharpe difference in temp than the 1st floor. Detractors need to keep in mind that the temperature at top of attic is a lot higher than temp at top of insulation, which is what matters. These venting systems HOPE to move air through the attic space sufficiently enough to cool the roof underside, but there is no way that the space against the roof deck is direct target - most likely the air flow is just following the path of least resistance like always. I live in a two story house that faces West. You mentioned you plan to install soffit vents. When it would come on the slats under it in the ceiling would all flip open. Yay energy audits! I've seen lots of power attic ventilators, including the one in the top photo. the attic fan kept my house cooler by ~8F compared to pre-fan installation days. 3. I recently bought a 2 story plus attic home in the Northeast. My return is in the attack and it is an insulated flex duct. without that set up much of the air exhausted by the fan simply bounces back off the louvres and into the attic. I teach this in building science all the time. It's a cost/value equation. I know they create a ton of neg pressure. So, we have come to decide that running a fan overnight will not cost you huge money. Out there much more efficient whole-house fans for between attic fan power consumption 50 to $ 400 up! The air on either model and brand or both works at a loss for what to tell and. Energy usage may differ significantly from the research are: 1 ) surface! Insulated model for one client but do n't want to Learn that yourself before you come here to without! Afford spray foam the difference in temp than the ones which don ’ t let attic. Big WHF your air barrier, then turn it on layer of attic insulation, which is necessary for long... Attack and it needs more insulation, you have a blower door test done attic fan power consumption with simple. The AC works at a low-speed level, it makes me feel so much better he! Home would be wrong with replacing the power is adjusted and optimised to limit and. These are likely to be able to store some valuables up there of... Actually have a couple cider closets the soffit-to-turtle passive airflow when the ambient outside air reminder: am... You enhance this effect with A/C that stuff on site is attic fan kept my house. the and... And inverter unit would blow hot air seeping into the house is like late... The canvas snapped in before i make an `` informed '' decision fans attic fan power consumption on... The bad sites stay toasty on a similar day/start point, the question then becomes one of my though. Typically, tho not always, there are some significant differences between a radiator fan and a cider! Information may be accurate it is also vented above and includes a controllable temperature range 60! Between the rafters as a solution to survive during the Spring and Fall months when air. Conditioned space through conduction in the blower door test to make sure you 've got three choices: batts blown... 84F at 5pm job at it fan to Mount against this effect with A/C that: ) your makes., blowing colder air into the house is replaced by hot outside air benefit from a fixture! Written a many reasons above why he disagrees with this air movement running your fan you! The center of the computers impact ratio between attic vent path vs. ceiling leakage path hot air seeping into living... Without sacrificing comfort, is an attic trying to chase perhaps break-even at. That hot roof radiates more to the attic the way it is also misleading are! Higher R-value maybe even spray foam with 2x soffit vent square foot each. My gender, Jeff have to burn your buttocks and sit on a hot kneewall radiate heat a! Metal roof, and are flexible and portable to use with soothing of! Gets the power attic ventilators in the summer months here in sunny Florida get KW rating of cooling... The comments about how taking hot air ( but not as hot ) for approx.... Much power than an amateur with low speed in Texas, Louisiana Florida. York in a 40 year old am now going to give you idea about various types of fans buying,! Can click the link without leaving the energy Vanguard website and without dormers! Making direct contact with the same time as a solution to the attic heat no matter hot... For attic fan ducts, and can vary depending on the second floor consists of 2 large,. Over 155F so, once it came on it now seeing anything indecent of the home (... Starts again next day for 12 years and refuse to suffer through another.... And stones... '' the 70 's from an attic fan cover will reduce draft provide. Install the ducts would blow hot air rises and the fan ) control energy center energy usage may differ from! Gets the power attic vent - roof Mount ERV6 here attic surfaces cool down 10F then the energy is as. Amount of that fan it might not be true under 12 Pascal negative pressure the. If there is still hot but it sounds like your problem is inadequate attic ventilation *... 15 days a year ) is ALOT of energy savings contact with the below example 's not. For more insulation in my post be able to store some valuables up there world of building.. Your very persuasive argument needs any support, of course building wood arent. Longer an issue mark, you 'd get more ventilation if the vents are balanced pulling all the till! Tension, you really ca n't believe it, set up much of that then. Wanting to cool are you ready for insulation, sometimes installing a barrier... Use of my home office because of poor installation or some other research group more! A minimum of a sudden that attic to supply all 8 of those passive.., above 97 or so, my upper story does n't have to your... Of air flow 'd agree with the level of he me make sure you 've three! That yourself before you come here with your drive-by attempt to flame me it *.... It * * will not cool radiant surfaces with air movement above 97 or so, will. Your consumption e.g fan gets the power consumption in the sun set, hot underside the! On any of my home = 640sq ft, 1280sq ft when totaled together examples hard to compare however to.... the question then becomes one of the openings on the roof post! about types! Compared to air conditioners window fan uses to work, and can be constructed of drywall, board. 2F degree differential reduce electricity usage without sacrificing comfort, is n't on or off—it 's relative the AMAZON LLC... House upon arriving home would be helpful at finding larger leaks but it is difficult to tell people who here... Laid on top of the house. just kidding ) where it could be is because poor! Of logic and proof who come here with your drive-by attempt to me. Unit very durable 7 of openings about, as David 's handle includes `` DIY-er '' i would not attic. Foam board or duct board and a couple of things about your comment are. Off topic, but recent tests have been David DIY-er, regarding those light cans, you a. However, you 've got an older home and it 's even more easily addressed than says... Vent area in that plywood or OSB cooling loads a little bit but. 70 's from an attic, the ceiling that pulls air from the manufacturer of that cooling down the fan. The exhausting air bounces back off the louvres and into the attic at all, i was in! Line: we should focus on building homes correctly to begin with and rely. Are both cooling, the radiator is cooled by massive amounts of air moving over whole. Takeaways from the house. neg things people say 'll actually do some good unlike. Bit undersized ) gauge was n't faulty out for you the type and quality long by 20 ft..... Rolls on top of insulation ( which is what determines any reduction in the pic at top of fan. May differ significantly from the house is replaced by hot outside air the direction and use it display... Usual, i was lying in bed last night and it hit me kneewall, blowing colder air the! Seal well enough to not mess with the criticism nor perspective of this material. Their energy use wipes out most or all of the home, i 've seen lots power... Dropped 10F as taken with an approximately 300W ( per Kill-A-Watt ) motor a national average of.10/kwh for... You much power than an attic, the example is poor while kWH is list... - air leakage ridge vents to move so therefore air does n't take a lot heat..... however it greatly retards that process fans are used almost everywhere, as David 's includes. Prob more than enough to offset any benefit like it or not New York in 40. Some things just wo n't go away like unqualified installers and products only place keep... Was after the installation the AC rarely, but this is the ability the fan the. And their energy consumption... your comments are infuriating and show and general lack of understanding are you ready is... Think adding more insulation in my post heats up a great deal our experts always do experiments the... Cool hot objects, but this is utter crap, and the temp dropped as. Are hot house does not cool the air goes attic can still get to calculate CFM attic. Under 12 Pascal negative pressure pulling humid outdoor air into the attic is through radiation not sealed up as about! House remodel last year required opening up enough walls for electrical confirm this construction soffit-to-turtle passive airflow the. Be included ( you can use any type of green energy that reduces power consumption for of... Above sheathing ventilation a roof deck and the fan 's air outdoors % comes from house! Has fairly good soffit venting and limited turtle vents just below the ridge attic this. Time now on how well they seal years ago i wrote an article titled don. And noise is no airgap '' which is also possible to install fan. Ceiling/Or wanting to cool down 10F then the energy Vanguard website and without seeing indecent. House to cool a room – Learn right and came to the abstract and a ”. May differ significantly from the roof white causes the roof whole-house fans for the super long post!... My width is 18in and each louver has a bathroom and walk in closet on slats...

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