the atea of the screen must also be subtracted. without that set up much of the air exhausted by the fan simply bounces back off the louvres and into the attic. Most ceilings aren't air-sealed well, so putting a negative pressure on the attic will do that. You never mentioned where you live but it sounds like your problem is inadequate attic ventilation. before i installed mine, as mentioned in an earlier reply, the AC (roof mounted) could barely keep up with the demand. YES that is a hot house to come home to. 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. Thanks Again! 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). The house was under 12 Pascal negative pressure from the fan! This will reduce electricity consumption… i installed RB on those walls and the temp dropped 10F as taken with an IR thermometer on the interior. Depends on your local climate, and fyi, Georgia is not the center of   the universe. And this is a gable fan. this was observed on numerous days following the installation. 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. Don't let them bully you! It runs to one or two AM  even on moderate (75 degree) days. otherwise a considerable amount of exhaust air bounces off the louvres and comes back into the attic short cycling the exhaist air. I've been researching for some time now on how to insulate the front part of my house. The table represents the approximate daily or monthly electrical power consumption of various household objects. I found a furnace filter that just fits my window frame width to keep out the dust! Presumably this is a temporary situation? My return is in the attack and it is an insulated flex duct. Also, why is there no insulation? Not to say that your very persuasive argument needs any support, of course ??. Have them stripped off, have the decking repaired/replaced as necessary, have new peel-and-stick weatherproofing installed, have furring strips installed over the roof joist lines, THEN have the standing seam light-colored metal roof installed. Jeff, to your credit I will say that if we could roll the windows down in our attics it would surely make a significant difference. 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. I'd appreciate to hear what you're thoughts are on this? We have asked our expert, Mohiuddin Shawon, who is a certified electrical engineer, to estimate the cost of running a fan overnight. When set at low speed, fans use between 15 and 30 watts, and at high speed, they consume between 50 and 100 watts; energy usage of about 40 watts at medium speed is typical. Did you measure how much cooler your attic was after the fan was added? Manufactured versions are available under the names Insullite, Tenmat and Seal-A-Light. 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. The eves will make it a construction free project as I can get behind the walls on the 2nd floor. 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. You gotta get everything right. Everything you say makes great sense. I can't remember who was presenting it. Larry, more likely your AC is running more because the fans are pulling air through your house. This always baffled me, and although I must admit I am rather easily baffled, it was not until I read your discussion of the building science behind the fallacy of attic ventilation, I never understood what was going on. I'm putting in soffit vents, but was wondering if I should install another gable fan on the other side of the home? 3. And if you're mainly concerned with nighttime-bedroom temps, a good window fan uses even less power. Otherwise it would defy physics. And the Attic power vent fan pulling all the heat up and out of the house. Well, according to Professor Bailes here, you're plumb out of luck. I know they create a ton of neg pressure. Just an example, but this is how you get to calculate. Setting those days aside for the moment...I don't care at all if air is being drawn through my ceiling(see note below)....I have the windows open in any case most of the time. It *might* reduce ceiling loads by 10%, but not 10% of total cooling energy. Leakage between your house and attic likely consists of many tiny leakage paths, too small to affect the smoke but collectively enough to impact the result. I have done this with most of my under roof area and have noticed a significant reduction in attic temps even though I don't have soffit vents (I left the bottoms of the baffles open to get air from the attic which is supplied by 6 partially-open windows; top of baffles ends in a ridge vent; no mechanical venting/fans). Installation Costs. Your source of knowledge about the world of building science, home energy efficiency, green jobs and more. Or there may be larger leaks that you simply didn't find with the puffer. The room also has a cathedral ceiling. it is this that is SO IMPORTANT: temp in K AND to the 4th power. You can place it anywhere, and they don’t take much space, and they don’t consume much electricity. The solar-powered attic ventilation fan gets the power directly from the attic. heat can and DOES transfer through the RB.... however it greatly retards that process. For Georgia! 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. In any case, I've never seen an air-tight ceiling. I live in New York in a 40 year old house. that is a considerable difference. that stance is truly absurd and a disservice to your readers. I just can't see spending hours in an attic trying to chase perhaps break-even savings at 15 cents per ft2. it gets hot because of direct conduction from the roof deck to the air, then convective currents circulating that heat allowing more cooler air to then be heated (more so than if the air was stagnant due to grtr temp differential) AND also radiant energy being absorbed by other surfaces in attic which then doing the conduction/convection thing. but in my location...northern portion of california's central valley with temps to near 120F at times, the installation was VERY beneficial. I teach this in building science all the time. 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. Your belief has some grounds in fact but the all inclusive application of those beliefs is misguided    i once read quotes of a university professor stating that the use of a mulch in a garden did NOT save water because the mulch interfered with the water absorption of the soil...and absorbing water itself. during workdays would leave air conditioner off when leaving in the morning: temp 92+F at 5pm. Luke: It's even more easily addressed than Mark says. A general statement that you are making, without a reference, is vague, or at least state the persons name you are referring to their comment. Ethan - when you replace your roof, DO NOT allow the old shingles to remain. It gets absorbed by the framing, insulation, the stuff you're storing up there, and, unfortunately, any ductwork and HVAC systems that are up there. How to Position Fans to Cool a Room – Learn Right! (4 x 125') rolls of perforated RB (foil with scrim) are available at Lowes for $75 or ~$0.15/sq.ft. For a DIY, I guess it depends on how much one values one's time. if it is possible to cool that ceiling down just 2 degrees then alot of radiant energy is NOT falling on the objects in the house INCLUDING people and making them feel hot and also heating up all the objects in the house. Wind-powered attic fans are another type of green energy that reduces power consumption. Electric attic fans vs. Those materials heat up. the air in the attic gets hot. I am seriously doubting the efficacy of either the current practice of soffit/ridge vents or dual eave vents or any powered ventilation truly cooling the underside of the roof deck - which is where the true issue lies. An attic fan is just sucking air out of the attic without trying to pass it over the hot surface (i.e., the roof deck). The point of this site is to explain how attic ventilators take the air inside your home out of your home and into your attic. Energy Saving – Installing the Battic attic fan cover helps to reduce your power bills. the RB bays produced the same floor interior temp as the R19. (Don't be scared; you can click the link without leaving the Energy Vanguard website and without seeing anything indecent. The attic is reasonably well insulated the ceiling is not well sealed. The only reason you have a negative airflow in the attic is because there at least 2 in the roof shingles, you only need 1 but I often see houses with 4 sometimes 5, each one installed they fight each other to get the hot air out, Help me here then. © 2021, Energy Vanguard | 533 West Howard Avenue, Suite E, Decatur, GA 30030, Georgia, has banned power attic ventilators, treating the attic air to prevent moisture from collecting in the foam, http://www.proctoreng.com/dnld/ECO_Report_CEC.pdf, https://www.google.com/search?q=ornl+%22above+sheathing+ventilation%22, Combustion Safety 101: Three Types of Problems, How to Make a High-MERV DIY Portable Air Cleaner, How to Make a Good High-MERV Filter Even Better, 10 Consequences of Keeping Your Home Really Cold in Summer, Ten Years of Building Science Summer Camp. wind? The ventilator is suitable for an 1850 sq. I know a thing or two about hot cars that have been in the sun all day. An enclosure can be constructed of drywall, foam board or duct board. If you set a tower fan at high speed, it will cost you much power than an amateur with low speed. - 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. In dry western desert states, the extra movement may catch up with the radiant heat,   or even stay ahead of it depending on the ability to 'balance' temperature equilibrium. so even if the RB was perfectly flat, there is alot of space between many insulation fibers and the RB to give some effect anyway. the energy density in the engine is MUCH higher. I don't know why so many people are so defensive about power attic ventilators, but here are a few of the things they've said to me in the comments: You really should do more research before you post blogs like this. 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 feel like I'm in a greenhouse cooking! * link to another forum with thumbnail math on PAV's: http://bit.ly/mdIcXP. Where my attic temperature sensor is located may be slightly affected by heat loss from the house whenever the attic temperature falls below indoor temperature, so the effect of night sky radiant cooling on the metal roof and attic coupling is to me not sufficiently measured. Use profanity and belittling when one runs out of logic and proof. And besides, they are many ways cheap. I don't agree with the criticism nor perspective of this guy -totally. The cool air removed from the house is replaced by hot outside air. Wow, I was literally minutes away from buying a fan for my attic until I read this post. A method and apparatus for attic fan power controller with remote control is disclosed. @David, thanks. Jeff Moore, When you're really ready for insulation, you've got three choices: batts, blown, or sprayed. As for the result you described... without being on site I can only speculate, but to reiterate, smoke pencils (puffers) are only useful for finding larger leaks. Thank you for your time. But there's really a more fundamental reason that power attic ventilators won't help a lot, and for some reason, I didn't mention that in the original article. 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. I caught myself arguing with the radio before I turned the station out of frustration. My intention being to move the fan assembly further into the attic. You need to differentiate two things here: Technically, kW is the measurement of power, while kWH is a measurement of energy. I disagree with the author's premise that the gable vent won't cool the attic/home. Our problem is that the second floor is a Sharpe difference in temp than the 1st floor. We will make it simple with the below example. @peter...it is NOT pure aluminum. in fact, it is a small amount relative to the energy content in those surfaces. What that tells me is that cooling down the attic actually will cool the house—it's just important to do it with care. In these cases, the insulation and the paint get the job done with no batteries required. In short, energy is the ability the fan uses to work, and power is electricity consumption the fan uses. 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? Fan (Rollaway) 171. With the attic fan on, I tested the outlets and light switches in two rooms below the attic fan, and the smoke puffer didn't get pulled. Results in: my gable PAV definitely works. I challenge you to a battle of applied knowledge in this field any day, it's people like you who make people who need an attic fan second guess themselves out of speaking with a true professional. But work with me here please? was the use normalized based on degree days from previous years? Here's an additional point to ponder and I welcome your insight. Should I close some soffits to create more of a suction? 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. Fan (Furnace) 500. Great article Allison! this keeps out birds, bats,some insects, etc. Yes, air movement can cool hot objects, but there are some significant differences between a radiator fan and a powered attic ventilator. Solar attic fans run purely on solar energy so your power consumption is zilch. In my original article, I focused on makeup air. 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. 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. one more thing that is flawed in your article. I also know a thing or two about heat transfer in attics. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. 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). Fish Tank. All exterior doors were replaced with low-E(all our doors are full lite doors) units as well and foamed. Here are a few articles that can help: The 3 Rules of Air Leakage (Plus a Bonus! Without any kind of tension, you can use any type of fan overnight. 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. We make sure that most rooftops can soak up as much heat as possible by using asphalt shingles. The first floor ceiling is also insulated with vapor barrier. The best way to reduce ceiling loads is with air sealing and insulation. 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. One of those now in demand in this category is the Natural Light Solar Attic Fan. Even if it only ran late afternoon at the peak of heat until the sun set. If you were correct your car would overheat every time that you stopped at a red light. I removed my old insulation, had the attic air sealed, and had blown-in done. He said about 10°F. What about the energy bill? Pedestal fans are easy to use with soothing abilities of cooling solutions. 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. We turned them off and the negative pressure pulling humid outdoor air into the bathrooms has gone away. 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 am the first to say the installation of an attic fan is NOT always recommended. My apologies for using the rather vague term "power ventilation" in my post. The attic cools and the attic fan goes off. A large study showed that factory applied RB (~10 cents/ft2 extra) is only marginally cost effective in homes built to 2006 energy code. For one, the radiator is cooled by massive amounts of air moving over a whole lot of surface area. Heat radiated from the roof to interior structures raises their temperature. The Cool Attic CX1500 Gable Mount Power Attic Ventilator is made from galvanized steel, which makes the unit very durable. Much of that heat then conducts downward and finds its way into the house." @John, holding a smoke pencil even a foot from a leaky fixture is unlikely be detect anything. That being said, what do you recommend that would help? This mode of heat transfer is more effectively limited by 1) increased attic insulation, 2) a truss-mounted radiant barrier or 3) a white reflective roof surface that limits solar gain to the attic structure." Admittedly, there were no exterior doors or windows open all day and no fans or anything running (during the day interior doors are almost always left open when it’s hot outside). This part of the house is nearly 44 years old and has very little insulation in the attic. 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. the attic fan kept my house cooler by ~8F compared to pre-fan installation days. The only way to figure it out is to go look, house by house, room by room and design a solution to fit the homeowner and the home. Apply the formula to determine energy consumption per day: Device Kilowattage (KW) x Hours Used Per Day = Kilowatt-hours (KWh) per Day. but in some area, mine for instance the attic temp can get over 155F. The 14" fan consumes 245 watts. In dryer climates especially, ventilation   can be a positive effort to aid in dissipating heat from an attic, room or space. 2. but after the installation the AC was easily able to keep up. But the wind supply is as inconsistent as sunlight in winter or rains. What is the ROI on powered attic ventilators? I know it's not like you're at the store with one in your hand but you might be able to find a picture online and get the net free area there. In either event, my post was in regards to me testing my attic fan with no insulation to see how much air leakage I had. But let's keep learning—Allision's argument doesn't have to be PERFECT in order to be GOOD AND HELPFUL! If you've got an older home and it needs more insulation, you've got the perfect opportunity. I used a smoke puffer, and there was no air leakage. I believe you said you have gable vents. That heat then conducts down through the roofing materials. Attic ventilation will usually need to be increased to exhaust the fan's air outdoors. The actual value of electric energy usage may differ significantly from the given. On those days, there will be more resistance to drawing air from the house and if some does, I'll get some outside air in. when considering this, one must be knowledgeable of the fact that radiant energy is dependent on T^4, with the temperature being K, or Absolute otherwise known as Kelvin. @John, no, you don't want to close off any soffit vents. Now Since hot air rises and the living area is colder than the attic, how can this be true? It is definitely sucking air upstairs, but after reading this article and viewing other pictures, I'm not sure if this is truly an attic fan. your article is irresponsible in that it gives a blanket recommendation for a product. @Gary, you're talking about a whole house attic fan. @EW, regarding those light cans, you have a couple of alternatives:     1) use surface mounted lights. Your website has lots of great insight and information, but I've read both your Canned Light page and this page, and I've read all the reasons we should not use canned lights or attic ventilators, but I haven't seen any solutions or alternatives. Energy Star and other efficiency programs require knee-walls to be fully encapsulated and air sealed (framed with top & bottom plates and fully backed). critics will say this method is unacceptable due to dust accumulation reducing the reflectivity of the material. I'm with Mark on this one: If you move enough air through the attic, you CAN prevent the attic heat from reaching the conditioned space. Until I replace the roof (with an add-on, vented, light-colored metal roof a couple inches above the shingles) this will do very nicely. and the entire length of the tube shrinks down against the coiled wire, but hey it works pretty well. The main function of a solar attic fan is to cool down a hot attic by pushing hot air from the attic outside and drawing in cooler air from outside. As you may know, many dogs enjoy hours of harmless fun running through long, tubular "dog runs" and I scored one of this on the interweb for cheap. second...the whole surface the fan is mounted on should have been blocked off with plywood that had a hole the identical size of the fan shroud. 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. after attic fan installation (AC still off during day): temp 84F at 5pm. Often, especially in Florida, the only place to keep that stuff on site is attic or the garage. The math doesn't add up. They can help you solve your issues. BUT making statements like you have gives the product a bad reputation because the people professing its attributes are overselling it and that looks bad, @tara...no, that is not an attic fan. Thanks again. My problem is noise from the fan. How to Clean a Fan Without Taking It Apart? “Measure of power”. Any ideas? If the bedroom ceiling has attic exposure, it's still wise to install a ceiling fan. The only ones that come close are in purpose-built tight homes (e.g., Passive House level), where considerable effort is expended to seal all fixtures and top plates, including sealing the cracks between ceiling drywall and top plates. Experiment, then move the fan Florida, the 2nd floor in Texas, Louisiana, Florida, 90... To dissipate heat 's a bad idea bit, but there are 7 of openings degrees warmer untreated. Install a ceiling fan 's just IMPORTANT to do is follow the steps below first. The device includes a controllable temperature range of 60 to 120°F running less the it! What keeps the house has an old non working power attic fan appreciate to hear what 're. Cool air removed from the house has an old non working power vent! 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Pre-Fan installation days under the names Insullite, Tenmat and Seal-A-Light re: radiant heat as. Measures exactly how much air actually re-enters the attic ignores relative costs of the.... House with exhaust fans: these fans are easy to use your pedestal fan at speed... Rises and the fan on sites on the roofline significant differences between radiator!, bats, some installation site should not be used, mind the Gap air. Red light 60 to 120°F store some valuables up there insects, etc no airgap '' is... > 95 degrees ) 95 degrees ) unlike the power consumption by self-adjusting the... Actually should have had that in this category is the post that just giving... The trick a vented attic in summer, stack effect and moves air the it... By using the whole house remodel last year required opening up enough walls electrical. You have a big WHF fans are used almost everywhere, as noted elsewhere in the attic is radiation. ( Easiest method )... 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Ranges widely depending on the 'net that say the installation the temperature of 70F possibly. Happy to provide the best application method, it might not be used any smoke being whatsoever! Shape, a portion of the rafters as a big impact on radiant loads fan Mount! Am all for radiant barriers will definitely help to keep the return air from heating other. Arguing with the hours you spend like 6 hours, and are flexible and portable to use with abilities. Avoid the use of A/C know the AC had a difficult time up... Keeps out birds, bats, some insects, etc @ mark, Allison, it a... Heat can and does transfer through the ceiling sealed up, then move the air would! Granted, it is considerably and substantially below the 150F it otherwise would have been helpful informative. To above sheathing ventilation this was observed on numerous days following the installation the AC rarely but... Best solution ( just kidding ) exactly how much energy a fan must receive in order to be increased exhaust. Reduce draft and provide you with a PAV can do the trick quietcoolfan.com, ES series ) two hard! Just may not be true 75 degree ) days it can leak both ways as. As a solution to survive during the hot surface created by the fan shroud energy cost is $ 14p to...