I used a smoke puffer, and there was no air leakage. I'll install it well :-). My gable vents on each end are 300sq ft (prob less since I need to minus the louvers), either way totals 600sq ft with both gables. mark: Perhaps you should read the literature review of attic ventilation done by Danny Parker at Florida Solar Energy Center. I always thought a solar attic roof fan would help remove some of the heat in our second floor. The manufacturer should be able to provide you with the net free area spec. - 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. John, this was the same for the mechanical room that was essentially an enlarged portion of the same area. I installed a Tamarack sealed insulated model for one client but don't know if there is any data on how well they seal. The house has an old non working power attic vent fan. What that tells me is that cooling down the attic actually will cool the house—it's just important to do it with care. The cool air removed from the house is replaced by hot outside air. The attic cools and the attic fan goes off. 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). Get all the details on the Master Flow® Power Attic Vent - Roof Mount ERV6 here! =)     The big complaint that leads to an attic fan request is usually a hot second floor, which can largely be mitigated by air sealing the attic and installing a generous bit of insulation - drastically reducing conduction and convection. 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. © 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. note: I actually have a whole-house fan in the ceiling that pulls air from the house into the attic. 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. but there ARE times when a PAV can do the trick. Since the metal roof was installed this has all changed. It’s an affiliate advertising program designed to earn commission by advertising and linking to Amazon which helps us to maintain this website cost. Tower fans don’t cool the air, that’s why they use less electricity than any other cooling appliance out there. Not to mention when you enhance this effect with A/C. Please help me to understand, that although the attic fan is on, there is no insulation in the attic, the attic isn't sealed, why is the smoke puff test not reliable in this situation? True, but typical attic vent ratios don't provide NEARLY enough free area for a PAV to operate without creating a negative pressure zone in the attic, which is what sucks air out of the house. Or, is the measurement taken from the inside, the louvers are slanted, so from the top of one lover (can't start with the bottom of the louver since I am now behind the it facing the screen) to the one below it is 3 inches. Funny thing is, I was lying in bed last night and it hit me. Fan (Ceiling or Circulating) 88. ALSO, as the roof deck is cooled, even slightly, due to radiant energy being proportional to T^4, a LARGE effect can be had with a small difference in temperature in REDUCING the amount of energy that is radiated to the top surface of the insulation and keeping it at a lower temp so it can do its job better. Power Consumption In this article, we are going to give you idea about various types of fans and their energy consumption. was the use normalized based on degree days from previous years? (Don't be scared; you can click the link without leaving the Energy Vanguard website and without seeing anything indecent. certainly, some installation site should NOT be used. I didn't bother. How does heat get into the attic? Those of you who still believe otherwise should ponder the following exercise. Thank you Allison Bailes! ADDITIONALLY, before the install the air coming out of the ducts (rigid metal flex ducts with little insulation installed in the late 70s) when initially turning on air would be HOT for approximately 30s. Apply the formula to determine energy consumption per day: Device Kilowattage (KW) x Hours Used Per Day = Kilowatt-hours (KWh) per Day. it is this that is SO IMPORTANT: temp in K AND to the 4th power. Nor am I. I just haven't found good retrofit option yet. You're pitting your intuition against physics and data. :). Because HEAT ALWAYS TRAVELS TO COLD. 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. The cooler roof radiates and conducts less to the attic. Thanks for your comment! Fish Tank. David,    Thanks for your comment! thats like saying insulation doesnt work. We think of ceiling fans in terms of evaporative cooling of the skin. 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). It's the hot, hot underside of the roof and subsequent radiation. ?,    Here in the high, dry desert of northern Nevada, I am quite fortunate in being able to use nighttime ventilation for nearly all of my cooling. Incorporating a radiant barrier on the backs of knee-walls (typically in the form of foil-faced polyiso for durability) is not a bad way to go. You could get a blower door test to make sure you've got it airtight. However, to say imply they are ALWAYS inappropriate is shortsighted and ignorant. That's why pressure diagnostics is the only way to demonstrate the impact of the fan (or lack thereof) on house air changes. That's as true today as it was three years ago when I wrote the first article. Sources such as The Billings Gazette, Energy Vanguard, and Home Power all have articles that essentially say the same thing: attic power ventilators are simply not worth the cost and effort. 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. A neighbor gave me an elderly propeller fan with an approximately 300W (per Kill-A-Watt) motor. Nearly a hundred thousand page views and 93 comments later, it's still generating lots of heat. I misunderstood, thinking you were cooling the attic in order to indirectly cool your home. I'm sure you will tell me it's a bad idea. The electricity amount you consume with fans entirely depends on the choice you opt for. I've seen prices as high as $1 per ft2. Either way, regardless, I guess I don't have to worry since the attic is complete now, air sealed and re-insulated. 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? in some cases (maybe most) an attic fan can pull (some) air from the house to cool the attic . ), Mind the Gap - Air Leakage at the Top Plates. Best wishes and don't forget, "Sticks and stones...". Air displacement is a natural way to dissipate heat. People who think radiant barriers are magic: They're not. 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). sure this is still HOT but it is considerably and substantially BELOW the 150F it otherwise would have been. Thank you for the info! is in the building world, you really ought to check it out sometimes. you would be surprised how much air actually re-enters the attic without this blocking. Thanks again. Dropping the temp by 10°F would reduce the heat load to the second floor by 20% (of 750 BTU/h), so the attic fan reduces the conduction cooling load by 150 BTU/h, or 50W!! 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. We're getting off topic, but here's a link to the Houston study: http://bit.ly/1m4W792. Having a built-in steel propeller, it prompts consistent air circulation. The attic has fairly good soffit venting and limited turtle vents just below the ridge. one last thing is...if the AC is NOT on, the house is heating up. 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. Fan (Rollaway) 171. Glad I am not married to one. Thanks Skye. @John, there are a couple of things about your comment that aren't clear. The idea is to reduce electricity usage without sacrificing comfort, isn't it? What I find infuriating is people who come here to comment without understanding physics or what the literature says about this topic. One would think that a small amount of heat can reach the conditioned space through conduction in the wood truss members. @Mark, you are correct, my comment was intended for David-DIYer. To see if this might be so, I have experimented in my attic (about 1931, no soffit vents, ridge vent (roofers...) and 6 windows now partially open to supply outside air) by adding conventional pink foam attic vent troughs along the entire under-deck area to accelerate the air flow against the roof deck and reduce radiation into the attic space. We had been called in to solve a mold problem in two of the bathrooms, and those three fans turned out to be the main problem. I did read all the comments (took a while) and came to the same conclusion. I'd appreciate to hear what you're thoughts are on this? Here it is: 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. 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. 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. My intention being to move the fan assembly further into the attic. So why not? 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. Smoke can be helpful at finding larger leaks but it can't be used to prove a lack of leakage. EXAMPLE: ), inside temperature continues to climb, reaching the aforementioned 80* mark at perhaps 9-10 PM (?!?!). Or if you live it for a long time? Well, you seem to know as much about physics as you know about my gender, Jeff. @Steve & Bob: here we go again... this thread is about power attic ventilators (PAV's), not whole house fans! He found that the average cost will vary between 7$ to 10$. I've lived with this for 12 years and refuse to suffer through another summer. AC work is EXPENSIVE. To top off the extensive sun exposure, the master bedroom has a HUGE arched window that faces West and is on the second floor. of course we know this to not be true. However the affect of this roofing material change is remarkable elsewhere. i did not have time to read all of this but please be aware the air in the attic is much hotter than the air outside because it is heated by the same radiant effect you are referring to. 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. (4 x 125') rolls of perforated RB (foil with scrim) are available at Lowes for $75 or ~$0.15/sq.ft. 3. 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. It stores the heat all day long and at night it bleeds down through the ceiling into the living area. after the installation the AC would cycle on and off. Secondly, contact the manufacturer of that individual fan. 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. Obviously, the temps in the attic will make that location really undesirable. Did you mean to say that your ceiling is not sealed? You will find this rating in the product specification that is labeled bottom or back of the fan or product specification listed on the online if your purchased model is branded. The attic fan, by reason of being limited in scope, is smaller and more compact in size. You never mentioned where you live but it sounds like your problem is inadequate attic ventilation. but NOT always i understand. These are likely to be small with relatively low cfm ratings. looks like there is little insulation to begin with which would allow less resistance to airflow coming from the interior of the home. HOWEVER, energy WILL be conducted from the wood material to the air at the boundary of the two AND THEN convection currents will continue to transfer this energy to other parts of the attic space. The second floor consists of 2 large bedrooms, 1 bath, and a couple cider closets. this keeps out birds, bats,some insects, etc. this made a BIG difference upstairs (i typically minimize air conditioning runtime and find other methods of cooling)    also, i installed RB in the crawl space of my gf's house. Due to your blog, I am now going to pass on all that :) Your logic makes sense. The a/c runs constantly and the attic is unbearably hot during the summer months here in sunny Florida. If you were correct your car would overheat every time that you stopped at a red light. So I follow and agree with all points, however, my point in installing an attic fan, and everyone I know who has, and does, and wants to, is exactly because we want #3 to happen. 1/15 ton of AC would fix it. I'm going to say it because no one else will... Allison Bailes, you're an ASS!! 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. Now Since hot air rises and the living area is colder than the attic, how can this be true? My soffit vent square foot on each side of my home = 640sq ft, 1280sq ft when totaled together. I put in the attic ventilator and have not had this problem since. How about using an attic fan in a home during the Spring and Fall months when no air conditioning is on? 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. :-)", It makes me feel so much better that he used that smiley face at the end. This type of fan uses electrical energy to run, but the power consumption rate is surprisingly low, somewhere around 50 watts. I don't even know what to search for on Google. The Cool Attic CX1500 Gable Mount Power Attic Ventilator is made from galvanized steel, which makes the unit very durable. your article is irresponsible in that it gives a blanket recommendation for a product. G. How come my post wasn't accepted? The reduction at top of insulation (which is what determines any reduction in the conducted load) is typically less than 10F. skye, i may have the misconception i am attributing to you but i believe you are a guy... from what i can tell Allison is also a guy so maybe your marriage proposal is misdirected, @John, your question is valid. 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. The radiation gets intercepted by the top layer of attic insulation, which is NOT transparent to radiant heat. I use a window air conditioner in my home office because of the computers. They're dark-colored. You need to differentiate two things here: Technically, kW is the measurement of power, while kWH is a measurement of energy. Often, especially in Florida, the only place to keep that stuff on site is attic or the garage. @peter...it is NOT pure aluminum. Fans with inverter units consume less than the ones which don’t have. The link below takes you to the abstract and a link to download the 68 page pdf. 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. the majority of radiant heat received is more greatly IR. All of your info makes sense. In my original article, I focused on makeup air. 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. also, prior to the installation the AC had a difficult time keeping up (it was actually a bit undersized). 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. When it would come on the slats under it in the ceiling would all flip open. 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