All this being said, I agree that in most cases, air sealing, insulation and adequate soffit and ridge passive vents are most effective. After reading your article, I'm wondering how the Tamarack would work if I had NOT installed the attic fans. I remember the days at my parents house. It is valuable to have the data from those who have studied them recently. Anyway, great article!! Yes, as the insulation level increases the potential benefit from the fan decreases. Hi all, just purchased a house and noticed in my attic there is a box fan running constantly that is blowing air out through a vent. Reflective roofing, unlike powered attic ventilators, addresses the problem where it begins, Despite how fervently some people believe in them, powered attic ventilators dont pass building science muster. I was not asking about "whole house fans". If you install a powered attic ventilator, there is one thing you can be sure of: your electricity bill will go up. Q. The plans called for R38 in all ceilings, R19 in walls and crawlspace. I've looked at other houses in the area. Martin: Don't you mean it strongly pressurizes the attic? And, yes, unfortunately the AC equipment and ducts are in the attic. Although setting up fans in your attic will expel hot air, they won't help you prevent ice dams. Newer construction calls for some attics to be completly sealed, no vents. You can adjust the assumptions to fit your own case and run your own calculations if you want. Seemed to work great. If you want a big fan, you can buy one. Sign up for a free trial and get instant access to this article as well as GBAs complete library of premium articles and With all the home automation occurring, a plethora of products are beginning to emerge, but so far what I have found are registers controlled in individual rooms by temperature and humidity. There is a ridge vent, and one turtle vent. Forte says position a ladder or step stool so you can reach one or two fan blades. I live in FL, and I'm considering a fan to exhaust hot air from the attic. Exactly what the name suggests. All these seem to operate on 24 volts. If you have ductwork in a hot attic, the best solution is to transform your vented unconditioned attic into an unvented conditioned attic by installing insulation along the roofline. Blowing in additional insulation is not an option at the moment financially. A. Then you know that a powered attic ventilator can pull dangerous fumes from a water heater into your house. But the outdoor air is the source of the moisture -- so that proposed solution is clearly counterproductive. I don't recommend the installation of a whole-house fan in any attic that includes a furnace. This one was sold at Costco for a while. Moreover, it is certain that operating the new fan you want to install will increase your electricity bill, because fans use electricity. I would be very happy to assist you in a thorough market overview which I do regularly for the http://www.WholeHouseFanGuy.com. Your'e definitely right, they survived without insulation (the old open-flame floor heater probably got quite a workout back in the day!). But in the real world, we look for practical solutions that people will actually implement. I also have a well insulated attic floor. Yes, of course more insulation with no moving parts and year round benefit is the better option. Response to Cathy Shin How Attic Fans Work Attic fans pull in cooler air from outside your home's building envelope its external structure and insulation layer, including the walls and roof while pushing the hot air inside the attic to the outside. First, inspect the existing ducts. Higher insulation levels would require an insulation coffin in the attic, which leads to greater surface area and greater heat loss area. This past summer,a major outdoor renovation forced me to disconnect the condensing units from the central A/C, leaving me with just the small window unit. I have a 3 level spit house. It is a low slope ashpalt shingle roof with deteriorated batt attic insulation. Response to Bob Barnum I am looking at installing an attic ventilator fan, radiant shielding, new ducts and blown in insulation to combat the problem. And what's what the "tight ceiling" claim over and over again? Crawl space, typical !8" Good. With the sun constantly beating down on the roof of your home, and your attic heating up, your roof and shingles are being scorched on a daily basis. Can an electrician do this job?f Thanks so much! And I accept your assertion that you have no financial interest in promoting powered attic ventilators. But I was wondering if I would just be better off installing a ridge vent along that main roof/attic. 2. Since I've already wasted $1050 for the two attic ventilators, do you think there's a way I could extend the wiring & install an indoor manual controller on the two ventilators & open the access hatch into the attic fully & just turn the ventilators on once it has cooled off outside? Attic fan reduced my electricity bill The inspector also found a bit of mold in the attic, which he deduced came from the non-working attic fan, his logic being that if the fan worked, there would be more air circulation and no mold would be able to grow. But we also love our air conditioning and low humidity . A few inches of re-used rigid insulation above the roof deck and batts of fluff between the rafters is less than half the cost of doing it with a combination of spray polyurethane &/or spray polyurethane + fiber blown in mesh. The house gets oven hot in the summer. Since air takes the path of least resistance, some of it will most likely be coming from the conditioned space in your home. Response to Richard James Even with this, we do not often use the a/c, the ceiling is insulated with R-30 between the joists with an additional R-13 or R-19 run across the ceiling joists giving a total of about R-45. Newer construction calls for some attics to be completely sealed, no vents. Repeat this on all the blades and test the fan for noise. Here at GBA, we strive to advise readers of the simplest and best solutions to common building problems. That 20,000 kWh would go a long way toward operating a pair of thermostatically controlled, powered attic ventilators (operated off the same thermostat) that had fans both blowing air into and out of the attic, through gable vents, with a balanced pressure so that air was not sucked through the ceiling of the house. People who live in old, uninsulated houses make compromises all the time. I imagine this hole would need to patched. I'm sure you will tell me it's a bad idea. What are my options? I'm not sure where you are thinking of installing these "motorized registers." (For more information on this type of ventilation fan, see Designing a Good Ventilation System.). I think so under some very specific circumstances. We are still waiting on that estimate to arrive three days later. As a result, the fans increase the homeowners' energy bills during the winter. Interesting article. If you don't know what type of air barrier or insulation has been installed in your cathedral ceiling, you'll need to investigate further. Just the numbers and how to build reasonably changes. Response to Kaye Kittrell #66 We moved to Kauai about a year ago. I have plenty of soffit, ridge and gable venting to allow the air to escape under the pressure. No Soffit vents Your house has many problems. Our house has no attic, just ceiling space and roof. For instance, filtering dirty air through the edges of your nice carpet and wall outlets. Q. During an average summer the outdoor air's dew point is above 65F about 1/3 of the time, and above 70F about 10% of the time, but there will be days-long periods when it's above 70F for the majority of hours, which is pretty uncomfortable. The opening to the attic from the garage has been left open, and the attic fan is quite nearby the opening, so obviously we're pulling outside air directly into the attic. With the screened vent opposite the fan, it seems I wouldn't get all that much draw from the interior of the house, and if I did, it would be cool outside air anyway. Since the discussion here recommends against an attic venting fan, I have another idea for consideration. Of course, doing both is nice. In what year were those studies written? http://www.tamtech.com//store/tc1000-h-whole-house-fan-brown,Product.asp. There are code complaint exhaust fans available w/dampers but displacement of the air has to be addressed, especially since I have a gas WH in the garage, as most CA homes do. Thanks for your comments. Who cares what your attic temperature is? No point in the insulation alone, once cellulose is in it is a pain in the butt working around it. Whether the investment in the equipment can be justified is another question. ". The usual way to vent an attic is with soffit and ridge vents. If the attic fans didn't do the trick, then I'd move on to the next solution and be out only $100. Again, I recommend that you disable the powered-attic ventilators. How often should I run it? Response to Scott Widdows My home is in the Sacramento CA area. Let's say it costs you $5 a month (or $35 a season) to operate. This assumes that there is a cooling system in place and operating. We have no central AC, but do have 3 window AC units that can help to cool those individual rooms. Q. I am a general contractor and all systems were upgraded to modern and very energy efficient units. By the time I go to bed, the attic is cooler than the inside of my house, so it is drawing heat out. Response to Kay Alldone If your house has an unvented conditioned attic, then your attic is just another room in the house -- just like a bedroom in a finished attic. "Since the desert southwest is prime territory for whole house fans and a common building style is flat roofs with either no attic space or very minimal, non-accessible attic space, what is an appropriate detail for installing a whole house fan?". The primary reason attic fans are not helpful is that they can depresureize the attic and draw air out of the house. Q = A U T = 37.7 0.038 40 = 58 Btu/h. Locate the screws that attach your fan blades to the housing, at the end of each blade closest to the fan assembly. That said, if we examine the heat flow across your hypothetical R-100 attic insulation, we will find that the heat flow is so small that any heat flow -- even if the attic is at 160 degrees F -- into the conditioned space below will be so low that it doesn't represent much of an energy penalty. In North TX and OK (where wife grew up, and West Texas attic fans were great. Checked them and replaced the filter pads in the spring when un-winterizing the systems.) But if you're having a heat wave, and the average temperatures (night and day) are above your comfort level, eventually everything is going to get hot, indoors and out, with our without insulation. "Should I install soffit vents, or just add more turtle roof vents?". If you are worried that your ceiling is still warm, the solution is simple: pile on a little more insulation. That seems a bad move for using the fan. My article provides several links to studies by researchers, including researchers at the Florida Solar Energy Center (FSEC) and Advanced Energy in Raleigh, North Carolina. "Am I correct in noting that a properly 'conditioned attic' would have zero vents in the roof? Recently we have found that by opening the (east-facing) garage door in the afternoon and turning on the attic fan, the house seems to be cooled a bit, without turning on the AC. 2) My mother-in-law stays in her hot home all day and was considering replacing her central A/C system with one of higher capacity. The discussion was centered around powered fans and vents. Listen to the Sky News Daily podcast while you scroll for discussion on 'greedflation' and what . My guess is that way more attention should be given to creating a flawless air seal around the cover than to adding a few more Rs to the R-value. On the middle level (living room/kitchen)(this section of the house has a semi catherial ceiling) . The article says of R-5, "Clearly, thats not enough insulation." With the gas furnace taking it's combustion air from the attic, running the fan will also result in air moving through the furnace's burners and heat exchangers. if late in the afternoon the house temps rise above the outdoor air temps there is actually a cooling benefit. Grew up with one in the 60s in NY. whole house 'attic fan' Asphalt shingles and other asphalt-based materials are the reason attics get so hot. If you have radiant barrier sheathing, the temperature difference between the two spaces won't be very great, and probably won't be enough to justify the use of the fan. Response to Chris Grabowy Experts say we'll still be paying 1,000 more a year on gas and electricity than before COVID. Between your comments and Martin's, it sounds like this isn't really the best idea for my setup. Rusty, He said the same thing. And the few times I use my AC. I was convinced it would never work in Florida, but Danny Parker [from the Florida Solar Energy Center] convinced me otherwise, said Springer. So I guess there would have to be a duct from the fan discharge through the roof. There are many reasons to doubt that your proposed fan installation will change the temperature of the attic enough to save any of the energy required to operate your air conditioner. Since I would need only 5 or 6 of these, that seems like an optimal solution if it can be easily retrofitted using a low voltage system and I can find something relatively affordable and controlled by the thermostat rather than these products designed to zone a system. Once more, I will repeat one of the basic themes of this article: If your ceiling is hot during the summer, then your insulation layer is too thin. Quieter radon systems. What really happens is that when that power attic ventilator runs, it's going to pull air from wherever it can find it. Well, to me two anecdotes are For more information, see Creating a Conditioned Attic. Also note that solar fans are available in gable vent models that could be installed in push-pull pairs - so no depressurization. We just had our shingles replaces with white energy-star shingles, and had the attic floor insulation brought up to code. According to the ASHRAE Fundamentals book, such areas include Idaho, Nevada, Utah, and Wyoming, as well as most of Arizona, California, Colorado, Montana, New Mexico, and Oregon. We still believe this is a good idea. It's so hot that it's impossible to work there in the summer. Even at 10 or 11 at night, when it was comfortable outside, turning the AC off in those rooms meant that they would quickly heat up and become very uncomfortable. "Will installing additional venting to attic solve the icicle problem?". Instead, you want a whole-house fan that is run when the outdoor temperatures are low -- not when the attic is hot -- and you want that fan to have a wall-mounted switch that you can control. Arnie Katz's study concluded that (an undefined amount of?) Thanks and follow-up question The attic "coffin" you mention, which is used to air seal and insulate pull-down stairs, scuttle hole, or a whole house fan, is good in theory, but in practice, is cumbersome to install. Humidity is generally miserable. The only way be reasonably comfortable was to be in one the of rooms with the AC and have it running. Duct dampers that can be installed at the boot in the ceiling could also work. Response to J Wing In your next case -- a hypothetical house without any AC -- does an attic fan make sense? In that scenario, calculating the insulation area based on the rough opening seems reasonable to me. Thanks for the input. A. I'm just keeping my fingers crossed that my particular home & conditions might allow the attic ventilators to be sufficient. to reduce chances of positive pressure pushing air into the house. There are even some Kickstarter ventures that have products on the verge of release. Thank you Martin. Do you have actual references? Condensing gas or propane furnaces with electronic ignition and piped-in combustion air don't have either these issues. Strip off all of the deteriorated insulation and throw it away. As a curious professional, I was willing to risk the investment to see for myself what effects are. This seems like an approach that could also limit depressurization. A blower-door test will tell you more about your air barrier details, and a few small inspection holes will tell you more about your insulation details. I never had a problem with icicles before the new roof and gutters. Their company doesn't do that so we would need to find someone else. Continue reading to learn whyor just skip ahead to learn how to cool them off here. Inside temps probably 80-90 degrees at that time, outside temps 70-80. Attic bedroom with no AC but a gable fan Once you get your attic floor insulation up to the minimum code level (R-30 in Florida), it really doesn't matter very much what your attic temperature is (with the usual proviso: you shouldn't have any ducts or HVAC equipment in your attic). Whole-house fans are sometimes confused with ventilation fans that provide fresh air. A long-term improvement to your house might involve converting your vented unconditioned attic into an unvented conditioned attic. Read the other comments on this page, or do some Googling -- you can buy a whole-house fan that is designed to be mounted in a sloped roof assembly. One mistake in the remodel was installing the furnace and duct work in the attic and heat is transferred from the attic to the ducts and then to the house. But he said that we would still have the same problem again because the attic was so hot. https://www.greenbuildingadvisor.com/qa. I have lived with the current flawed system for 8 years and it is not that bad, mostly because of our moderate climate where temps rarely exceed 90. For more information, see the articles below. An HRV or ERV that provides fresh ventilation air to the indoors in all seasons. But personally, I'd go for better than "tolerable" - install a mini-split and use it sparingly. Sorry about the diatribe. Walk barefoot on an asphalt road and see how that works. The problem is not the hot attic but the ducts in the attic. Your estimate of 15 to 18 years is much closer to the average here (as it appears to be in Texas). I picked one inch of foam in my example to match the R-5 mentioned in your article. Use a large diameter, high-velocity fan for the stairs. Thanks very much for your comment. I have an area of wall where I can install it, so I won't need any holes in the roof. The first step would probably consist of installing some attic insulation. I am not making conclusions as to the relative difficulty of either of those approaches, but a quick look says that to insulate 2000 ft^2 of attic space to R-38 vs. R-30 has a marginal cost of about $375. Derek, Talk about wasting energy! What Is an Attic Fan? Let's break down each one below. Asphalt is a great material for absorbing solar radiation and has poor thermal emittance. There is just no way around that. Does everyone you know live in a dilapidated log cabin? If anyone has any comments to this, feel free to pick it apart. Theres a lot of confusion surrounding attic fans. Saving energy and needing insulation is the same. If I create an unvented conditioned attic, then the house fan is just moving air into that conditioned space, correct? I am considering, if such a product is available, installing motorized registers on each duct where it enters the room so they are normally closed, but open when the air conditioning system starts. The attic, apparently like most on the island, doesn't have any insulation. In an attic with gable vents, soffit vents, and ridge venting, I suspect that the attic fan would not create a significant pressure difference and the air leakage from the house is probably small. With the summer season upon us, now is a good time to review an uncomfortable topic. ", http://www.buildingscience.com/documents/reports/rr-0302-roof-and-attic-ventilation-issues-in-hot-humid-climates I think I will still need it at times to reduce garage temperatures regardless of insulation and passive ventilation improvements. If the fan lowers the indoor temperature, why not use it? The attic ventilator was much cheaper, so I opted to get two of these installed & see what happened. The key is solar reflectivity and thermal emittance of the roofing material. Heat conduction from the attic to the house is proportional to the temperature difference divided by the R-value. Is that correct?". You wrote, "Insulation can only slow and not stop the energy transfer. Split AC as in, "not a package AC.gas-furnace" unit. The interactions of the stack effect, wind, HVAC equipment with duct leaks, and attic fans are complicated and unpredictable. http://www.atrendyhome.com/romowhhofano.html, Here is a link to a Tamarack fan that is optimized for air sealing (and that provides high-R shutters controlled by a motorized operator): How important is insulating the fan cover? It worked ok, but slowly, so last year I installed a 3,200 cfm house fan in the same location. This means it can only cool 1-2 rooms, not a whole house. This is something we intend to remedy prior to winter. I'm going to try to repeat what you wrote to see if I understand correctly. On the theme of creating positive pressure in the attic and displacing hot attic air with cooler exterior air, ventilation fans designed for foundation ventilation could possibly used in place of 22.5 inch eave vents to push in exterior air and thereby push out attic air through high gable vents and eyebrow vents. Most need to be connected to a 120 volt power source, but there are also solar powered fans available, such as the one pictured below. Q. Your thoughts? Attic Fan Ventilation. Attic ventilation does not deserve the attention it has received in relation to shingle durability. If your clients prefer cool shingles to warm shingles, the amount of ventilation behind the sheathing is far less important than the shingles color; so advise them to choose white shingles. If you push hot air out of your attic, more hot air from inside your home will just rush in and . "I read a little about back-drafting.". Over 5 months, that would total 878,400 Btu, or 257 kWh. There is literally no access to the attic, though I've cut some test holes to see what's in the space. A powered attic ventilator has a different purpose: it is designed to lower the temperature of an attic by exhausting air from the attic and replacing attic air with outdoor air. However, if your attic has blocked soffit vents and is not well-sealed from the rest of the house, attic fans will suck cool conditioned air up out of the house and into the . Q. So, the trade-off varies depending on your climate of course. To answer your questions: (a) No, I have never installed a Tamarack fan, and (b) I have no affiliation or financial relationship with the manufacturer (and neither does GBA). Solar-powered attic fans hold a strange fascination for many homeowners, especially homeowners who are worried about their attic temperature. J. Freeman, My house built in 1965 3 level split NE Ohio. Q. As you suggest, lay persons are jumping into PAV's without doing proper research and the on line vendors are not helping with this problem. Attic Ventilation Fan Your comments about Tamarack are surprising. The first steps to addressing a damp basement are to make sure that you have roof gutters connected to conductor pipes that carry the roof water to a location far from your foundation, and to adjust the grade around your foundation as necessary so that the soil slopes away from the foundation in all directions. What would be wrong with replacing the power attic fan. Your argument rests on three legs. The best way to limit heat transfer across the thermal boundary (the attic floor, in this case) is to make sure that the thermal boundary is air sealed, and that the insulation is very thick. If it doesn't -- fix the panel. Thanks for the follow-up response When moving to ELP it wasn't initially natural to open the windows in the rooms you wanted to cool, and close them when the room is not in use. There was one large flaw with the fan though, while the large fan duct was insulated and it had a damper on the end that exhausted to the attic, the heat build up in the attic caused heat to flow back into the house and would noticeably warm the house during the day. The space is more friendly for air handlers located there. Whole House Ventilation Does everyone you know live in a dilapidated log cabin? This feature has been temporarily disabled during the beta site preview. Exhausting moderate amounts of attic air (as solar fans do) can counteract this, reducing infiltration (my calculations show it to be about right for a vented attic, but either do the calculations or measure the pressures). Your article comes across as biased. Maybe in the future if/when the unit needs to be replaced. Believe it or not, many homeowners with powered attic ventilators leave them running all year long, because they forget to turn them off or the thermostat breaks. Gable Attic Fan: Entirely located in the attic, a gable fan mounts vertically on the home's existing gable.When signaled by the thermostat, it turns on and pushes built-up attic air out of the gable. For the benefit achieved, creating an unvented and conditioned attic is way too costly and complex. The exposed area of this box is therefore 26.6 square feet for the sides, and 11.1 square feet for the top. Video of the Day. Attic ventilation fans protect your attic from mold and mildew, help cool your home, and can make your roof last longer. Increase your ventilation area, or consider a different solution. Recent code changes allow unvented roofs and unvented attics, but most attics in the U.S. are vented. I'll have to check to see what kind it is. Green, I currently open the downstairs door and stick a box fan in an upstairs window and it cools off in 5 or 6 hours. He said that those two sections would be replaced and rewrapped. I don't think I'd ever be running them at the same time. There are two sections that are showing condensation and this dripping water. First, we need to distinguish between three different types of ventilation fans. That paper notes, "Data measured at FSEC and elsewhere show that attics with nominal natural ventilation and [at least] R-19 ceiling insulation do not need powered vent fans. The potential back drafting even while the burners aren't active can crud-up the burners with rust/grit from the flue, leading to high CO emissions (and lower combustion efficiency) when the heating season arrives, etc. Response to Tom Barrett We keep it turned off at the fuse box, to keep it from potentially causing other problems. When the control predicts relatively mild weather, the ventilating blower will run at a lower speed than when hotter weather is predicted. Also, like many of the homes here, our house isn't built directly on a foundation. A. However, the cost was prohibitive, so I installed an attic fan. (Yes, we insulated and sealed the vent (drained the water and cleaned/painted them inside in the fall. Just not sure what to do. That's why the energy required to run an attic fan is wasted: the attic fan consumes much more electricity than any possible saving from reduced air conditioner run time. Energy regulations for new equipment phased out standing pilots as of 2012, but that was the industry standard type of furnace ignition 20+ years ago. I'll be building a large garage with attic storage in NE Texas. Insulation can reduce the rate of heat flow from the outdoors to the indoors. Is that correct? I picture the Tamarack blowing hot air up into the attic, which joins the cross-ventilation and carries it out of our attic. They come with both a fan and small vents, accomplishing two things at once. I have emailed the manufacturer of the home asking for any information they can give me. "In his recent book, Water in Buildings, Rose summarizes what he has learned from years of careful research: Does ventilation significantly reduce shingle temperatures? Response to Micah Morgan My attic temperatures get extremely high over our 6 month summer. who cares how hot the attic is? Bottom line, for my unique circumstances the PAV works, a bridge to the next step. Response to Penny Dorneman If we keep everything else equal, this is 1/17th of the insulated area in your calculation, so the rough cost differential over a season drops from $18 to just over $1, for the cheaper heating source. This approach can be supplemented by adding more insulation on your attic floor. My house in ELP had a roof top swamp cooler that was attached to the ducting in the house. After all, if you're sitting in a hot room and turn the ceiling fan on, it just moves the hot air around. Basement? The condenser/compressor unit is outside, and the evaporator coil is in series with the gas furnace. Even though a manufactured cover costs more, it is far easier to install.
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