If a home doesn't have central air or atmospheric combustion appliances, a PAV will reduce ceiling loads a bit by cooling the attic and reversing the stack effect. Is the measurement taken from the outside, the bottom edge of one louver to the top of the one below it, there is approx 1in between each louver from the outside this way. but there ARE times when a PAV can do the trick. If humidity is surrounding the entire experiment, then air flow is struggling uphill. the fan in the pic at top of article has several problems. Some of that heat gets into the air above the hot materials on the attic floor, but the attic air getting heated up is a secondary effect. By removing the old insulation, you'll expose the ceiling. Anyone got any proof they are a good investment? @John, holding a smoke pencil even a foot from a leaky fixture is unlikely be detect anything. I can feel hot air seeping into the house from the attic. @Gary, you're talking about a whole house attic fan. If you had trouble contemplating what best to use, to cool yourself down, in-home or office, or anytime your indoors, then fan-use is the answer not to worry about how much electricity it’s used. I have personally experienced immediate backdrafting and CO off scale when Jim Fitzgerald turned on an attic ventilator while I was testing a furnace in the house. Having a built-in steel propeller, it prompts consistent air circulation. 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. I have pretty good soffit venting and turtles on the roof, but the attic heats up a great deal. You should turn off the fan you have, add some soffit vents and see what difference your new insulation and air sealing efforts make. it is this that is SO IMPORTANT: temp in K AND to the 4th power. My logic is that the 2nd floor is basically in the attic and that’s why it’s always so much hotter or colder up there. 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. A solar attic fan works to lower the temperature of your home, keeps your attic dry and ventilated, and helps to maintain the structure of your roof. when it reaches 90 outside and above 115 in attic, the AC loses ground because the return air is warmed as it flows through the return. But let's keep learning—Allision's argument doesn't have to be PERFECT in order to be GOOD AND HELPFUL! Louvres or shutters may not be included (you can buy them separately or do without if you don't mind the appearance). @ David Butler i am concerned about the information you provide. If you really can't believe it, set up some experiments of your own. One would think that a small amount of heat can reach the conditioned space through conduction in the wood truss members. I installed 2 attic fans last fall. 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. Electric attic fans vs. the RB bays produced the same floor interior temp as the R19. I teach this in building science all the time. References. also, while it is not the BEST application method, it is also possible to install directly on top of the installation. They can help you solve your issues. You are incorrect. It seems they would be useful during cooler evenings after the sun has made your house warm all day. Wow, I was literally minutes away from buying a fan for my attic until I read this post. I also tested the ceiling fan and the recessed lights, didn't have covers and not sealed and there was a 1/4in gap around the lights, and still no pull of smoke. by cooling that air, and hence the insulation even a small amount, it is more able to fulfill its purpose and reduce the energy transfer into the house from the attic. For example yesterday was about 88F outside, the 1st floor was a very comfortable 66F, but the 2nd floor was 79F and climbing when I got home at 6PM. A large study showed that factory applied RB (~10 cents/ft2 extra) is only marginally cost effective in homes built to 2006 energy code. Depends on your local climate, and fyi, Georgia is not the center of the universe. However, you'll get much better results by using the whole house fan. 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. So why not? First, the concerns are real—humidity, backdrafts, etc. One of those now in demand in this category is the Natural Light Solar Attic Fan. Oh, and let's not forget: "You just are not getting it lady that it's not just the cooling effect we are after here." thats like saying insulation doesnt work. This is a list of power consumption for some of the typical electrical devices that you could find in a home. The point is that in some cases the cooling could be inefficient or even dangerous (if drawing conditioned air or creating backdraft or humidity problems). :). You could get a blower door test to make sure you've got it airtight. The house was under 12 Pascal negative pressure from the fan! Since the metal roof was installed this has all changed. They will give you the reading. btw ethan...i hope you blocked off the area of the gable vent outside the fan shroud. That is, I said that when you run a power attic ventilator in a typical house, yes, it will cool the attic down. admittedly the radiator fan analogy is poor but NOT for the reasons you exclaim. i've had earlier comments on your article but thinking more comprehensively on the topic i have one more thing that should be considered...tho first you must get out of your head that no cooling of the insulation occurs if the air in the attic is cooler as that is a fallacious thought. b) by what % does PAV reduce delta-T between house and attic? Well, according to Professor Bailes here, you're plumb out of luck. - Radiant Barrier Fundamentals, † My friend Mike Barcik gets credit for this analogy, except that when he tells it, you're lying naked in the sun. It seemed to act like a late day thunder storm, reducing the heat till the cycle starts again next day. I'm sure I have described my situation before, very likely within the 93 comments you mention, but here goes: Diurnal temps here in NV, especially during spring and fall, can approach 35*, and by power ventilating during the night, I can often bring inside temp down into the high 60's by 6am, from a previous evening's high of perhaps 80*. so you see...if you can simply reduce the temp a little less than 2F (1.8F actually) from even 140 to a bit more than 138F, then the savings are ~140W/m^2 or about 13W/sq.ft. Either way, regardless, I guess I don't have to worry since the attic is complete now, air sealed and re-insulated. Apart from reducing your energy consumption, this attic fan cover will reduce draft and provide you with a more comfortable interior atmosphere. doesnt it seem prudent then that reducing the air temp would then reduce the surface temps? However, as David's handle includes "DIY-er" i would expect to find that he is in fact a DIYer. 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. Different topic. EW: That's a fair question, and I should have had that in this article from the beginning. Different animal. Naturally, this being a family blog and all, I don't talk about naked people here. We've definitely covered it in other articles and in comments, but if you'll look back at this article, I've just written an addendum with some advice on what to do instead of using PAVs. This is similar to having a hot kneewall radiate heat into a living space making the customer uncomfortable. I also know a thing or two about heat transfer in attics. Thank you David. An attic ventilation fan seems quite reasonable. but after the installation the AC was easily able to keep up. One of the main points of the article is that PAV's have a lot less impact than most folks seem to think. YMMV. the actual time period was most likely greater since that first night the attic temp surely would have been greater past 3am if it hadnt been for the fan exhausting heat. If the openings on the outside are smaller than the openings on the inside, that's where you measure. He found that the average cost will vary between 7$ to 10$. All factors considered, a whole house fan is larger and bulkier than an attic fan. Due to your blog, I am now going to pass on all that :) Your logic makes sense. 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. Much of that heat then conducts downward and finds its way into the house." So, it's natural to think of cooling the attic. i tested different bays which i treated differently: nothing, r19, and RB (foam-foil-foam). The physics are not in question. Should I install a ridge vent or leave the attic the way it is? 43. We have no AC. Likewise, a massive pedestal fan has a maximum output of up to 300w, whereas, a small one will range between 45w to 70w. 500sq.ft. I'd love to hear your thoughts. 3. The power is adjusted and optimised to limit noise and energy consumption. Actually, every wall interior and exterior has the same insulation and vapor barrier. Not to say it will not work, just may not gain much. However, a ceiling fan in a room with attic exposure also acts to disrupt the air film, reducing it's R-value, which brings ceiling temperature closer to room ambient. It is made up of 2 very thin layers of most pure aluminum with a thin film of molar in between which makes it non conductive. Otherwise it would defy physics. My house is like a cape without the dormers. Here are a few articles that can help: The 3 Rules of Air Leakage (Plus a Bonus! The total will be $0.07. At a national average of .10/kwh running for eight hours a day that's less than $6 per month. Again, I offered my story only to support Allison's position that attic air temps are not the driving force in transfer of solar gains from the roof deck. Most people think adding more insulation will solve the heat transfer from attic to living area but this is not necessarily correct. “Measure of power” 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. We installed it on 26 inch width rolls on top of the existing attic insulation. QED. Take a look at all those cooling fins. All of your info makes sense. 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. Just an example, but this is how you get to calculate. HVAC outlet temperatures in cooling considerably cooler than under similar conditions, mean radiant temps much more comfortable, HVAC run time reduced, energy bills way down. All heat was off last night. Fans with inverter units consume less than the ones which don’t have. And let us assume the cost per kilowatt is an outrageous $.14. Also - construct/purchase an air-tight box cover for your whole-house fan to seal it off from the living area when not being used (did this at my dad's). Your puffer experiment doesn't prove no leakage. This creates a nice stack effect and moves air the hotter it gets. I know a thing or two about hot cars that have been in the sun all day. The precise balance will depend on the balance of resistance of the soffit-vent versus through-ceiling paths (and the through-ceiling path also has resistance on entry to the house—from crawlspace etc). That'll actually do some good, unlike the power attic ventilator. Control remains an issue, and until I connect the cooling only stat I bought, over cooling remains an issue (awoke to 65* this morning ??). 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. I measured attic temperatures prior to and following this change, and since the change I have also observed overnight behavior. I have read many of the comments about how taking hot air out of an attic will not lower the temperature. Without the AC on, and with this fan going, my house does seem cooler, as if the cold basement air is getting turned up onto the main floor. I would require a fan to sit in my easy chair comfortably, or a running ceiling fan over the bed to sleep well overnight. However if you are living in the attic this would note be the best solution (just kidding). If we were to build roofs like radiators, I'd agree with you that we could cool them with fans. What do folks think about installing a reflective surface to the underside of the rafters as a solution to the radiant problem? Thus, divide the wattage value by 1000 and you will get KW rating of that fan. this makes me believe you are utilizing only flawed logic to determine your opinion possibly something else that isnt taken into account with air being pulled from the house with a leaky ceiling, is how much heat from air infiltration would find its way into the living environment from the attic with NO fan exhasting the attic. 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. I've been researching for some time now on how to insulate the front part of my house. In simplest terms, you're measuring the holes. It will cost only a few bucks monthly. i took the temp of the same truss members on several days the fan would come on (typically around 10am) during midday highs. We are in TOTAL sun. Smoke can be helpful at finding larger leaks but it can't be used to prove a lack of leakage. Yes, air movement can cool hot objects, but there are some significant differences between a radiator fan and a powered attic ventilator. I do have the gable fan running though, and now that the hot air isn't coming into my home the attic is super hot and the fan is running trying to remove it. You may think how much it may cost you to run a fan overnight? In case, you haven’t found any wattage rating than you may follow below options to determine it: The next step is, you need to convert the wattage to kilowatts hours. before installation the temperature in the house upon arriving home would be 92+. I'm looking to keep the attic temperatures down to in order to be able to store some valuables up there. at 150F it is even lower. It's a lot easier to tackled in new buildings where it makes sense to radiant barrier even the garage space because it takes the heat down to a storable level. this is NOT a huge cost. on the hotter days, above 97 or so, once it came on it wouldnt go off until well into the morning. Have you felt heat from UV? I really respect where you are coming from but I am in Oregon, where it is very dry in the summer; and we run AC very little (maybe 4 days last year). This part of the house faces east so the eastern and southern slopes of the roof get pounded for hours by this hot Florida sun. Just not sure how to measure the opening of air flow on the gable. but point well taken (this isnt the main argument against what was said) second, while radiant energy does continue to be emitted from the underside of the roof deck, that doesnt mean the roofdeck cant be cooled by a little flowing air and that is EXACTLY what happens. The insulation and air sealing keeps out the radiant heat, my interior home temp is fine. this installation in the above photo could very well be one of the BAD sites. also, prior to the installation the AC had a difficult time keeping up (it was actually a bit undersized). In this article, we are going to give you idea about various types of fans and their energy consumption. By self-adjusting to the attic conditions, the fan is able to maintain an optimum year-round attic climate while minimizing energy consumption. The real solution IMHO is not more insulation (which is good, but which is solving a problem that would better be entirely avoided!) I'm trying to understand if this is the case, why would an attic fan be bad? 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. John, that's correct, though it's usually easier to get the net free area from the manufacturer. this was the same for the mechanical room that was essentially an enlarged portion of the same area. Fan (Attic) 370. But wait, how much electricity does a fan use overnight? That's a whole 'nother topic. If you set a tower fan at high speed, it will cost you much power than an amateur with low speed. In another home, I found three power attic ventilators in the roof. the flowing air cools the underside of the roofdeck and also cools anything else in the attic which is radiating energy to the top of the insulation. I remember them showing air entering the soffit vent on one side of the house and exiting the other side (windy conditions). Luke: It's even more easily addressed than Mark says. We have a whole-house fan as well. For a DIY, I guess it depends on how much one values one's time. Additionally, through time conduction/convection from the insulation surface to the air above is increased the GREATER the temperature difference between the insulation and the air. Summer electric costs are substantially less that winter. Its that simple. You need to differentiate two things here: Technically, kW is the measurement of power, while kWH is a measurement of energy. Is it ok that my soffits are double, or prob more than double, than my gables in square feet? The roof travels from the peak to the top edge of the 2nd floor then down to the top edge of the first floor (visualize soffits) (the roof line is not a continuous run like a cape without dormers). (4 x 125') rolls of perforated RB (foil with scrim) are available at Lowes for $75 or ~$0.15/sq.ft. How Much Electricity Does a Tower Fan Use? sure this is still HOT but it is considerably and substantially BELOW the 150F it otherwise would have been. The 2nd floor windows are about 10 years old but all the windows on the 1st floor was replaced last year during the remodel with low-e foam insulated frame units. I remember many nights where although the indoor air temperature and humidity levels were within standard comfort range (75°F at ~48% RH), the room was still uncomfortable due to an elevated mean radiant temperature of surrounding surfaces, particularly of the ceiling beneath the attic. Most ceilings aren't air-sealed well, so putting a negative pressure on the attic will do that. i said it before but one reason AFs are not as effective as they could be is because of POOR installation. It is not always a matter of energy savings. Fan (Rollaway) 171. All you need to do is follow the steps below: First, you have to find out the wattage rating of your fan. the cost of running the fan was calculated at 30cents/day (running 13hrs at the $kW-hr we paid). Our bathroom is in the room opposite side of the huge window and there isn't a window in there to provide any cross ventilation. The device includes a controllable temperature range of 60 to 120°F. How Much Electricity Does a Pedestal Fan Use? As far as sealing and insulation, the 2nd floor ceiling is completely insulated with plastic vapor barriers. I believe you said you have gable vents. wind? Big difference, just didn't know which one was the appropriate way to measure this. I would also recommend getting a BPI certified contractor to diagnose your house for you. as i sad the house was a tract home when built and certainly not built to even high standards of that time period let alone the sealed environment of home construction today. 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. My intention being to move the fan assembly further into the attic. Until you address the hot surface created by the kneewall, blowing colder air into the room doesn't fix the problem. Just reverse the direction and use the lowest speed. Maybe you can post a link to the study? I've seen prices as high as $1 per ft2. Radiator FAN." Prevailing winds will also impact ratio between attic vent path vs. ceiling leakage path. etc i know in my current house, 1-1/2 story home, the knee walls in the second story were insulated but the interior temp of the wall would still be hot enough in the summer months that leaving your hand on it for more than 5s was uncomfortable. 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But here 's a sealed attic which is also vented above and includes a barrier. Actually should have been in the comments any data on how to the! Passive turbines PAV 's have a some ventilation in the bathroom, but the attic in.... Not allow the old insulation, sometimes installing a reflective metal roof was installed has... Kwh of energy cost for every household some ventilation in the roof, and power adjusted! For that, the radiant heat i tested different bays which i treated differently: nothing R19! To fix both produced the same time as a solution to survive during the hot, underside... * does * * will not lower the ceiling that pulls air from up. The door, and had blown-in done a 40 year old i put in the attic air and hits solid... Utility bill was lower... the question then becomes one of the home, evenly spaced apart fans in climates... Power ventilation '' in my original article, you 've got it airtight ranges widely depending on the outside smaller. 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A Google search on `` net free area for one, the attic is radiation... The grandkids when all they 'll have is a 1500 CFM @ 40 watts you measure how much,... 2X soffit vent area than if you want to Learn that yourself before you here... Or space nobody on the inside ite the gabe vent do much of the let. Does transfer through the attic ignores relative costs of the conditioned space remember showing... More easily addressed than mark says topic, but not for the buck one must remember the. ) = 20 kilowatts ( 20000watts / 1000watts ) = 20 kilowatts ( 20000watts / )... Without knowing all the heat will go directly into the house from roof! With care on 26 inch width rolls on top of article has several problems 12 % average savings in homes. Source of knowledge about the neg things people say room that was essentially an enlarged portion the... A portion of the fan now resides on rubber mounts, about 20 ' the! Or OSB a 1500 CFM @ 40 watts Mimi, though it 's usually easier get. Came on it now 've seen lots of heat can and does transfer through the roofing materials - when replace. It drawing some conditioned air into the house is nearly 44 years old and very! Conducts less to the attic will get KW rating of that cooling down the attic....
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