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Q&A Spotlight

Should We Install a Whole-House Fan?

A building inspector raises concerns about depressurizing the house

Whole-house fans are designed to remove hot indoor air and replace it with cooler outdoor air. A homeowner in Minnesota wants to include one in his new house, but the building inspector is raising objections. [Image credit: Fine Homebuilding]

Writing from St. Paul, Minnesota, W Ramsay wants some feedback on his plan to install whole-house ventilation fans in the house he’s building. He likes the idea, the building inspector does not.

Ramsay sees the benefits of improved indoor air quality and energy-efficient cooling, while the inspector is apparently concerned that the fans would depressurize the house and possibly lead to backdrafting of combustion appliances.

Originally, the inspector was prepared to require a 1:1 makeup air system, which would not only be expensive but also defeat the purpose of the fans, Ramsay says. The inspector backed off that original request as long as Ramsay could guarantee that a sufficient number of windows would be open while the fan was running. More recently, the inspector says he wants an engineer to guarantee there would be enough passive makeup air for the system.

“Is a whole-house fan beneficial?” Ramsay asks. “To me this is a very easy ‘yes.’ On some days we can get enough air through our house with natural breeze, but many days there is either not enough breeze or it is coming from the wrong direction.

“A whole-house fan creates the breeze and with windows open provides fresh air, reduces or eliminates VOCs and CO2, and cools the house for a lot [less] energy and dollars than running the AC,” he adds. “Am I nuts?”

Further, Ramsay wonders whether a whole-house fan could be considered dangerous. He says he found one instance in which a whole-house fan had been linked to a death; the victim was a high school student who turned on a fan after smoking marijuana but didn’t open any windows.

Are any of these concerns well-founded? That’s where we start this Q&A Spotlight.

Whole-house fans are great

“What’s not to like?” asks Zephyr7. “I love whole-house fans,” he writes.  “They work great to quickly cool a house off at night. They work great to bring in fresh, clean air, and they’re cheap to operate. In northern areas, whole-house fans can often replace air conditioning during the spring and fall.”

The only potential for danger that Zephyr7 can imagine would come from the spinning fan blades themselves. As long as Ramsay keeps his hands away from the blades, Zephyr7 isn’t aware of any safety concerns. Based on his own professional experience, Zephyr7 suggests that as long as an open window is at least as big as the area of the fans, air pressure inside the house won’t be an issue.

“It sounds like your inspector is going a bit overboard with your fan project,” he says, adding that it wouldn’t be very difficult to add a sensor that would prevent the fan from operating unless a certain number of windows were open.

“I can’t see why your inspector would be trying to require anything more complicated,” he says.

Use common sense in hot, humid weather

To Dana Dorsett, the efficiency of nighttime ventilation with a whole-house fan depends on how it’s used. When outside humidity is high, a fan may bring in moisture from the outside and increase latent cooling loads. But most people can figure that out by how the air feels, he adds.

“Nighttime ventilation schemes can be very efficient in drier climates like the West Coast states,” he says, “but just make it clammy indoors in much of the Eastern states, deriving a higher indoor relative humidity than using a modest amount of air conditioning.”

With those humid conditions in mind, Dorsett adds, it’s not clear whether a whole-house fan would always use less overall power than 20+ SEER heat pump/air conditioner, such as a cold-climate minisplit.

Fears of negative air pressure

The inspector’s worries seem focused on the risks of negative air pressure in the house and the potential for backdrafting from fuel-burning appliances. The inspector seems intent on getting some type of documentation that would guarantee that Ramsay’s plans are sound from an engineering point of view, and he’s unmoved by Ramsay’s arguments.

“We also tried to explain to him that there are no engineering studies on this because they are not a problem,” Ramsay says. “Tens of thousands are installed every year and they aren’t a problem, and aren’t viewed as a problem by other building inspectors.”

Further, adds Zephyr7, the axial fans used in whole-house fans aren’t capable of generating negative air pressure.

“It really takes a centrifugal blower or positive displacement pump to generate levels of negative pressure that can damage things,” he says. “If your inspector is worried about negative pressure causing structural damage, it just isn’t possible here. If his concern is backdrafting in combustion appliances I suppose that is a valid concern, but also easy to address.”

Backdrafting, of course, isn’t an issue with sealed-combustion appliances, which have their own source of combustion air separate from the air inside the house.

“Yep,” replies Ramsay, “we’ve talked with him about that. This is a code issue, not a physics issue. And physics does whatever code and code inspectors say it will do.”

Martin Holladay’s 2012 article

GBA editor Martin Holladay notes that he provided advice on this question in his 2012 article, “Fans in the Attic,” which included this paragraph:

“Because they depressurize a home, whole-house fans can cause atmospherically vented appliances located inside a home — for example, a gas-fired water heater — to backdraft. If the homeowner remembers to open plenty of windows before turning on the fan, backdrafting probably won’t occur. But the best way to avoid backdrafting problems in a house with a whole-house fan is to make sure that the house doesn’t have any atmospherically vented combustion appliances.”

Some other points to consider

Timothy Tucker’s house in southeastern Michigan had a whole-house fan when he moved in, but he removed it a year later because the uninsulated 1990s-era fan was causing more problems than it was solving. He wonders whether Ramsay would be better off spending the money he’s set aside for fans on solar panels instead and lowering his electric bills that way.

He also raises these points:

  • If Ramsay already has another system for circulating and filtering air — for ventilation or for central heating and air conditioning — why introduce another? A whole-house fan is only practical in warmer weather, so it might make more sense to focus efforts on something that works all year ’round.
  • A whole-house fan is designed to flush hot air out of the house and replace it with cooler outside air. But if the outside air is tainted by industrial pollution or high pollen counts, recirculated air from a central AC system might be cleaner.
  • In moderate temperatures, a ceiling fan can make the air feel cooler than a whole-house fan. Moreover, a ceiling fan uses considerably less electricity and costs far less than the Tamarack whole-house fan that Ramsay is considering.
  • Installing central air conditioning plus $1,500 in solar panels will likely have an overall lower cost than central AC plus a whole-house fan. Or, investing the cost of a whole-house fan in air sealing, better windows, or more insulation offers year-round payback in comfort.
  • Noise pollution may be an issue. Although Tamarack fans are much quieter than some of the old-school options, they still make more noise than most central AC systems, ceiling fans, or single-room exhaust fans.

Our expert weighs in

Peter Yost, GBA’s technical director, added these thoughts to the mix:

In just about any climate, but particularly in a cold and relatively dry one, if I were to cut a decent-sized hole in my top-floor ceiling and stick a fan in it, I would be make sure that when the fan was not running, the opening was air-sealed and well-insulated. Tamarack Technologies has been making high-performance whole-house attic fans for a very long time and it’s a great family-owned business.

Frankly, it never occurred to me that there was a safety issue with makeup air. So I called Nelson Warner, vice president of R & D for Tamarack Technologies. “In more than 20 years in this industry, I bet I have gotten only a handful of questions about ensuring makeup air for our attic fans, while I am inundated with calls regarding makeup air for kitchen range hoods,” says Warner.

I figured if makeup air for whole-house attic fans was an issue, particularly one that a building inspector chimes in on, then the issue would be covered in the building code. I searched my copy of the 2018 International Residential Code extensively, and found only this one reference: “M1501.1. Outdoor Discharge. The air removed by every mechanical exhaust system shall be discharged to the outdoors in accordance with Section 1504.4.3. Air shall not be exhausted into an attic, soffit, ridge vent, or crawlspace. Exception: Whole-house ventilation-type attic fans that discharge into the attic space of dwelling units having private attics shall be permitted.”

That’s it. There are plenty of detailed requirements for other mechanical exhaust systems, particularly ducted ones; for example, M1502 (Clothes Dryer Exhaust) and M1503 (Domestic Cooking Exhaust Equipment).

And then Warner sent me an excerpt from the California Energy Commission (CEC) Residential Compliance Manual of January 2017. While the model building codes have little information on or requirements for whole-house attic fans, there are plenty of requirements on this type of equipment in the CEC residential manual:

  • 7.10 (Ventilation Cooling) has essential background information on whole-house attic fans and central fan systems.
  • 7.10.1 (Whole House Fans) has detailed informantion on the different types of these fans (ones with simple barometric dampers; ones with electronic dampers that air seal and are insulated; ones with remote fans for noise reduction), including energy standards and listings in the Energy Commission’s appliance database.
  • 7.10.3 (Prescriptive Requirements): Under CEC Component Package A for CA climate zones 8-14, a qualifying whole-house fan is required, and must to meet the following eligibility criteria:
    • Whole-house fans must meet combustion safety requirements related to indoor gas-fired appliances (essentially an interlock for gas-fueled appliances that aren’t direct-vent appliances or sealed-combustion appliances).
    • The fan must be listed in the Energy Commission’s database (as stated above).
    • The installation must meet net free vent area requirements for attic ventilation (Tables 4-20 and 4-21). The worry is not about makeup air but about sufficient attic vent area to prevent pressurization of the attic, with the primary concern being disruption of attic insulation.
    • The homeowner must be provided with a copy of a “How to operate your whole-house fan” informational sheet. (An example from the City of Davis, California, can be found here.)

It sure seems to me that something as simple as a cover plate for the attic fan switch having this warning would work: “Do not operate this fan without first opening windows.”

Warner cautioned me that many fans nowadays have remotes. OK, print the same warning on the remote. And for smart phone app operation? OK, add a pop-up screen on the app with the same warning.

And then I found this information resource from the U.S. Department of Energy on whole-house attic exhaust fans. It aligns pretty neatly with the position California has taken.

In any event, the state of California seems to have this figured out well enough to prescriptively require whole-house attic fans in a component package for Climate Zones 8 through 14. Qualifying whole-house attic exhaust fans can be an efficient form of cooling, particularly in the right climate, and can be easily operated safely.

Information on California climate zones: California has 16 climate zones. An example of a Climate Zone 8 location is Long Beach, with 1400 heating degree days (HDD) and 1200 cooling degree days (CDD). It’s somewhat tempered by its proximity to the ocean, experiences no frost, and gets 12 inches of rain per year, mostly in “winter.” For Climate Zone 14, let’s use the example of Barstow, California: 2500 HDD, 3000 CDD (medium to high desert), less than 12 inches of annual precipitation, and wide temperature swings, with frost common in winter. It appears as though Climate Zones 1–7 are very mild and coastal; Climate Zones 15 is low desert; and Zone 16 is a large semi-arid mountainous region.

14 Comments

  1. Lance Peters | | #1

    I suspect the cost of an attic fan installation would pay for a lot of electricity to run your standard AC with, or as has been suggested, a small solar array to offset the home’s electricity bill.

    When all aspects and options are considered, I would be surprised if an attic fan makes sense in anything other than very specific climates.

  2. Jason D | | #2

    I live near Denver and have a whole house fan. No matter how many windows I open, it ALWAYS trips off the furnace back-draft sensor if both the fan and furnace are running at the same time. I simply turn off the furnace before starting the fan. (The only time this is an issue is when we're trying to clear smoke from cooking.)

  3. David Eakin | | #3

    Costs vs benefits are definitely location dependent. Here in the Mid-Atlantic the shoulder months are too unpredictable to guarantee an overnight benefit from whole house fans so the benefit here is too slim.
    One other point - I'm very surprised that there has been no mention of home security. We do not live in a high crime area but are constantly being advised by local law enforcement to keep our windows and doors locked overnight to prevent home invasion. I would think the only way a whole house fan could be used without jeopardizing home safety is if there were bars installed on all the windows you intend to open (which would then add additional costs and jeopardize emergency egress). Seems like a losing proposition.

  4. Wayne Falcone | | #4

    I think that the whole house fan can be a energy benefit, but there must be an insulated box installed over the fan when not in use to reduce heat losses. The 3 ft hole in the ceiling will allow heavy heat losses as the only thing keeping the heat in the house from rising thru the opening are the thin aluminum flaps..
    I always recommend building a box with rigid foam insulation on the inside, hinged at one side & a rope & pulley at the other side to raise & lower the box with the rope from a hallway closet when you want to use or turn off the fan.

  5. JasonScheurer | | #5

    As a Building Scientist that specializes in Deep Energy Retrofits, my company takes out whole house fans and then we properly air seal the attic to separate it from the house, then insulate to a minimum of R44 at the attic floor, or move the insulation to the roof rafters (dense pack via BIBS) and make the attic conditioned space. All while checking our work and progress with a blower door for best practices.

    The reason for this is to stop the heat from coming into the house in the first place.

    STOP PUTTING BANDAIDS ON A BULLET WOUND.

    Building Science is not BS, it is proving your work is done right.

    If you follow your ASHRAE 62.2 Residential requirements, and properly air seal and insulate to required depths, whole house fans become a myth. Just add your required balanced HRV's and you will stay comfortable year-round.

    PS- Make sure your HVAC is a sealed system and Manual J on the design and it is amazing that your theory on Whole House Fans go Bye Bye.

    1. Brian Schreiber | | #8

      "follow your ASHRAE 62.2 Residential requirements, and properly air seal and insulate to required depths, whole house fans become a myth"

      OMG. . . Goodness. Do you you have a wife? Have you ever come across someone who simply cannot stand to be cooped up in a closed box all day and wants. . . get this: FRESH AIR!

      We live in the country, in Minnesota. Our need for fully conditioned air, as in AC, is limited to a few, often, continuous weeks in late June / July-- 4 max. From the time the ice goes off till frost is on the pumpkins we have a varied number of windows open. When AC is required I finally do, in fact, shut all the windows and run the Mini-split. Otherwise, windows are open and importantly early evening and up to about midnight we run the 700 cfm exhaust fan in the kitchen to emulate a whole house fan.

      New home 2017; I got around the BS from the local inspector whining about a whole house fan by simply roughing in the access port in the ceiling but have plans to eventually install a Tamarack WHF which DOES have R60 insulation covers for shutting over the winter. This may never happen because even with the severe under-rating of the kitchen exhaust we mostly are covered for needs of COOL fresh air. In this situation, with our boiler / water heater system having ducted in combustion air, there is NO reason why a whole house fan is not a savings over AC. We save MANY weeks of AC and cost of fresh air filters by using this simple method.

      Some of you folks on this "forum" are just too zealous while not considering human reality.

      What do you do when you go camping by the way? How is it possible for you to live? Will you be requiring Kelty and Northface tents to install CO2 sensors, makeup air, and particle sensing along with complying with ASHRAE 62.2 Residential requirements?!

      1. Lance Peters | | #13

        Unless you absolutely have to have that open window breeze and need to hear birds chirping, and ERV/HRV will provide your house with all the fresh air you need. As an added bonus, the air will actually be cleaner, too, as it's filtered as it's drawn in. Oh, and you can still open a window in a house with no Whole House Fan, so it's not like you have to have one to experience that open window feeling.

        Do you plan to have AC as well as a WHF? If so, the cost of installing both is pretty high and the added cost of the WHF could pay for many years of AC. As mentioned in the article, putting a small solar array in place instead of the WHF would not only cover your AC costs, but pay for itself over time.

        Another drawback with constantly opening your windows is the amount of DUST that gets in. When we open our windows for just one day, if there's a decent breeze blowing our entire freshly cleaned house is covered with a layer of dust. It's especially bad in the spring with all the pollen in the air. Some people don't see dust and/or are not bothered by it, but if you're opening your windows all the time it's surely there.

        A WHF may be a great solution for you and your wife, but there are lots of reasons why they are not a good solution for everyone, and many places where the climate just makes them ineffective.

  6. Charles Campbell | | #6

    "...a cover plate for the attic fan switch having this warning would work: 'Do not operate this fan without first opening windows.'” I have an AirScape fan and see that there is only room for a 2" x 1/2" label on my cover plate, and I'm having trouble finding a custom label that size. Who makes them? Must I buy a label maker?

  7. Gary | | #7

    The house design is important. Growing up, our whole-house fan was in the ceiling of the attached garage. To operate, you opened the door to the garge and large windows in the house. It did an excellent job pulling air all the way through the house, and cooled down the attic. But importantly, when not in use there's minimal issue of losses through the fan opening, as the air seal is that door.

    My current house has a mudroom separted from the conditioned space by an exterior door, in a climate that can definitely make use of a fan for significant portions of the year. My plan is to follow the same aproach by putting one in there.

    1. Brian Schreiber | | #9

      Great idea Gary. I also grew up in a home with a whole house fan, built in 1961. Huge louvered fan assembly in the main hallway. Man, when that puppy turned on it was loud. Your home's solution with the fan mounted in the garage is really unique and interesting. Your plans for the present home sound valid too. GO FOR IT.

  8. Eric Habegger | | #10

    This is an interesting topic about WHFs that seems to be fraught with bad info. WHFs are probably the most efficient way of conditioning the house air of any other method. But it's a very conditional efficiency that depends on many things. First, it usually requires a climate that is not too humid in summer because otherwise you will just be bringing in latent heat when you operate it at night. But there are a lot of climates in the western part of the U.S that are compatible with that. And if you are in the humid eastern part of the U.S don't make the mistake of telling us westerners that WHFs are no good just because they are no good for you. Another part of the climate requirement is that it (this is just my own rule of thumb) gets down to at least around 65F at night in summer except for maybe a few days.

    Second, it really helps to have a fairly tight and well insulated house, especially the more extreme the heat is in summer during the day. More moderate climates have a lesser requirement of "a pretty good house". Use your common sense to correlate how well built your house is to your use of a WHF and the climate it sits in. If you live in primarily a heating climate make sure you can seal up the duct for the WHF very tightly during the cold periods. Even in my cooling climate I temporarily install a sealed R-20 panel over the opening during winter. Contrary to popular belief thin louvered doors do not cause hot air to come down from the attic in summer. (Hot air rises, remember)

    I finally got my DER on my house finished and have my own results on the first really hot day of the summer - it hit 100F yesterday. The house is by no means a passive house, just 2.25ACH50, dense packed 2x6 cellulose walls, and R-40 cellulose attic. (DO NOT use fiberglass in attic if you want to stop heat from migrating from it as allows too much air circulation!) It got down to 69F in the morning and gradually got to 77F by the time I was able to turn on the WHF. It was easily accommodated by me with the use of ceiling fans. I made the mistake of having a slightly underpowered WHF for my house size so I'm not quite able to get the house temp down to the lowest temperature reached during the night. Don't make the same mistake I made. I can live with it though. I'm a pretty happy camper.

    1. Lance Peters | | #12

      A good, common sense approach. If night time lows are significantly lower than your desired indoor set temp and humidity is very low, a WHF could surely be a benefit especially in a well insulated and airtight house (and an ERV as you mention). Makes perfect sense.

      The better the house is insulated and the more the windows are shaded from the sun, the less temperature rise you would expect to see throughout the day. Your dense-packed cellulose walls surely have some thermal mass effect as well, which would slow the progress of heat through the walls as the day warmed up.

      1. Eric Habegger | | #14

        Yeah, part of the retrofit was building a south side porch with an overhang. It works well to shield the rays during the hottest part of the day. I also like porches generally to hang out in during the not so hot times of the year.

  9. Eric Habegger | | #11

    I guess I need to add one more thing that is a conditional requirement to make a WHF effective. The whole thing is dependent on a tight structure that has a thermos bottle effect on temperatures. I got a CO2 detector for my home and even with just a 2.25ACH50 it quickly goes past 1000 PPM if there are any breathing creatures in the house. Bottom line: you need an ERV or an HRV. Without an AC unit bringing in fresh air an exhaust fan won't cut it. While it will bring in fresh air you will lose the whole thermos bottle effect. I went from a bathroom exhaust fan to an ERV. It was a necessity.

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