With a hot attic, the ceiling heats the building. They are much more valuable when you have ducts in the attic and they make a bigger difference in an attic with little ceiling insulation. 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. Attic temperatures track right at or within a few degrees of outdoor ambient temperatures. this installation in the above photo could very well be one of the BAD sites. the cost of running the fan was calculated at 30cents/day (running 13hrs at the $kW-hr we paid). also, the insulation isnt a perfect surface anyway. We turned them off and the negative pressure pulling humid outdoor air into the bathrooms has gone away. Because HEAT ALWAYS TRAVELS TO COLD. 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. After reading your article, you seem to advise against it. Which is also why I must take you to task with this point: "Detractors need to keep in mind that the (air) temperature at top of attic is a lot higher than temp at top of insulation, which is what matters. " That one was hooked up at one of the gable vents. 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. the air in the attic gets hot. I hope I've painted a clear enough picture of the layout let me know if I need to elaborate. I have experienced a lowering of the attic air temps and lower radiant ceiling temps even though there is no direct path of outside air to the bottoms of the troughs. And this is a gable fan. Secondly, contact the manufacturer of that individual fan. I found a furnace filter that just fits my window frame width to keep out the dust! If one was to rely on a contractor to install it, the cost I find is exhorbitant and really not worth it. i think critics just like to be negative and hear themselves talk. ... (attic, etc.) Purchase a wattmeter and use it to display the watt reading. When it would come on the slats under it in the ceiling would all flip open. of course we know this to not be true. (4 x 125') rolls of perforated RB (foil with scrim) are available at Lowes for $75 or ~$0.15/sq.ft. NOTE: Comments are moderated. Will you marry me? (In summer, stack effect tends to draw hot attic air into the house). If you get one that is insulated and sealed, and you don't live in a humid climate, they can work really well. So, my net free area for one gable vent is 18in x 7in =126 sq in? The link below takes you to the abstract and a link to download the 68 page pdf. If you want to spend money on something, get your attic air-sealed and re-insulated. By self-adjusting to the attic conditions, the fan is able to maintain an optimum year-round attic climate while minimizing energy consumption. As far as power consumption is concerned, the ILG-001TH runs on 120V (10 amps) – which is quite in line with other products in the attic fan thermostat category. Installation Costs. f. attic. i installed RB on those walls and the temp dropped 10F as taken with an IR thermometer on the interior. These are likely to be small with relatively low cfm ratings. and, as the members of the roof trusses are cooled, they will also absorb MORE radiant energy from the insulation surface and the roof deck further reducing the temperature of both, tho i admit, this is a smaller consequence. With or without a thermostat, these attic fans are valuable additions to any home or property. So the attic heat no matter how intense cannot penetrate it, no matter how hot the attic gets. If you were correct your car would overheat every time that you stopped at a red light. However, to say imply they are ALWAYS inappropriate is shortsighted and ignorant. The most common mistake homeowners make when installing insulation is to block the flow of air at the eaves. I just feel that if there isn't a significant pull of air from the other side of the home then it will just take much longer for the one gable fan to pull all the hot air out, even with soffit vents. What you're describing with your baffles is similar to above sheathing ventilation. AC work is EXPENSIVE. My house was built in 1945 and our kitchen ceiling has what I assumed is an attic fan built into it. The issue in the summer especially, is the MAJOR difference in temperature in our second floor and especially our master bedroom. What is the ROI on powered attic ventilators? The cool air removed from the house is replaced by hot outside air. 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. We think of ceiling fans in terms of evaporative cooling of the skin. i think the recommended temp setting is 110F. R30 at 130F is around R19 if i remember right. It is not always a matter of energy savings. The wattage that are stated for them are approximate and can vary depending on either model and brand or both. @Steve & Bob: here we go again... this thread is about power attic ventilators (PAV's), not whole house fans! For one, the radiator is cooled by massive amounts of air moving over a whole lot of surface area. Just reverse the direction and use the lowest speed. @John, holding a smoke pencil even a foot from a leaky fixture is unlikely be detect anything. I would require a fan to sit in my easy chair comfortably, or a running ceiling fan over the bed to sleep well overnight. Essentially, I do have a whole house fan but because of the Rube Goldberginess of my set-up I was hoping to avoid full disclosure. At a national average of .10/kwh running for eight hours a day that's less than $6 per month. Second, nobody on the entire thread has suggested that an attic fan **will not cool the house**. Those materials heat up. Take a look at all those cooling fins. How to Position Fans to Cool a Room – Learn Right! Presumably this is a temporary situation? Expect to pay between $50 to $400 and up for an attic fan, depending on the type and quality.. If the bedroom ceiling has attic exposure, it's still wise to install a ceiling fan. You open the door, and the seats are hot. The attic cools and the attic fan goes off. 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. haha. The roof doesn't radiate directly to the attic floor. I've lived most of my life in Texas, Louisiana, Florida, and Georgia. 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. @Cameron, great point about impact of ceiling temperature on MRT and comfort. There you have it. The a/c runs constantly and the attic is unbearably hot during the summer months here in sunny Florida. It stores the heat all day long and at night it bleeds down through the ceiling into the living area. 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. If a home can have an insulation barrier, then move the air on either side, one is gaining. If you really can't believe it, set up some experiments of your own. in some cases (maybe most) an attic fan can pull (some) air from the house to cool the attic . Much of that heat then conducts downward and finds its way into the house. It definitely has to be equally larger and stronger. My question would be 'Would a PAV help keep my house cooler by venting the hot attic air and sucking in cooler air from all of the open air spaces in the ceiling and around the outside roof?'. Let me make sure I have my math right. I don't even know what to search for on Google. It's called life lessons 101. If you set a tower fan at high speed, it will cost you much power than an amateur with low speed. The electricity consumption of each type of fan is different as most of them have different wattage ratings. Is it drawing some conditioned air into the attic? So what are the solutions? Heat radiated from the roof to interior structures raises their temperature. the car radiator is using air to cool a engine block but is 2 steps removed (water cools block, fins cool water, air cools fins). On the few days when it gets REALLY HOT and I turn on AC, perhaps I'll lose some AC energy into the attic. It *might* reduce ceiling loads by 10%, but not 10% of total cooling energy. Energy Star and other efficiency programs require knee-walls to be fully encapsulated and air sealed (framed with top & bottom plates and fully backed). Not to mention when you enhance this effect with A/C. the result...118F. Control remains an issue, and until I connect the cooling only stat I bought, over cooling remains an issue (awoke to 65* this morning ??). Ethan wrote: "The precise balance will depend on the balance of resistance of the soffit-vent versus through-ceiling paths.". This is utter crap, and can be disproven by a 5 year old. hopefully this not not a "professional" job because it is pure hack. I remember the days at my parents house. WOW, so much misinformation...(not the original post, but the comments). This was a good tradeoff. 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 louvers should seal well enough to not mess with the soffit-to-turtle passive airflow when the fan is off. Most people think adding more insulation will solve the heat transfer from attic to living area but this is not necessarily correct. When totaled together which supports what you 're saying about where the air temp would then reduce the temps... Accurate it is difficult to cool by doing so has gone away and only then are ready! Thinking of disconnecting the fan should only have a whole-house fan would pull conditioned air being sucked from... 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