I just searched this forum for "Whole House Fan", but I didn't find much about them (except this and this).

I'm curious to hear what experiences you all may have with these simple and relatively inexpensive devices out in the real world.

Here are some pictures and a basic definition of the type of fans I'm talking about:

4.7.12 Alternative Systems - Ventilation Cooling (2013 CA Energy Efficiency Standards)

The CEC also maintains a list of models approved for sale in California. Does this list adequately represent the state of the art?

Or are there other emerging whole-house ventilation technologies that home professionals ought to know about?

For this discussion, let's try to not confuse an old school "Attic Fan" (which isn't designed to ventilate a conditioned space) with a "Whole House Fan" (which is).

Don't hold back!

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I think it is important to check the energy consumption of such a large fan, even assuming it can be properly air-sealed and insulated. We are finishing up a study on 2013 Code vs. Passive House in each of California's climate zones and, while a whole house fan was useful in some climates, it mainly decreased the number of hours air-conditioning would be required; the total cooling energy demand often did not decrease much. (This is in buildings with low cooling demand, since they have already been optimized with shading, thermal mass, etc., and include the T24 standard assumption of night ventilation through windows). In any case, moving cool air through a hot building is a pretty "low-output" process, due to the low heat capacity of air - this explains the large fans required. While many of people instinctively view air-conditioning as something to be avoided whenever possible, there are cases where a refrigerant or water-based cooling system may be more efficient than a whole house fan, particularly at higher CFM. We'll be presenting our study at the upcoming North American Passive House Conference in Burlingame, September 10-14 (http://naphc2014.phius.org).

Graham, what "large fan" are you referring to? 

I am fascinated by your comment "there are cases where a refrigerant or water-based cooling system may be more efficient than a whole house fan"

Can you offer an example?

I am vitally interested in learning more about T24. Can you help me as a consultant?


The "large fan" is a whole house fan moving anything from 1000-4000 CFM. By comparison, the ventilation system for the T24 prototype home we modeled was 67 CFM. As you might imagine, a fan that moves 1000-4000 CFM could use a lot of electricity. We have not yet examined this in detail, but you could imagine that as the fan increases in size, diminishing returns are found, i.e., suppose 1000 CFM cuts the cooling demand in half. An extra 1000 CFM would reduce the cooling demand further, but not by as much as the first 1000 CFM. The next 1000 CFM would help even less and, at some point, the cooling brought by the fan power required to move the air could be less than the same power an efficient air-conditioner might use to do the same job. This situation is increased in a building where the cooling has already been reduced by other measures, since much of the "low-hanging fruit" has been plucked, so to speak.

Again, I am hypothesizing about this, and suggesting it be studied since I have not analyzed these numbers specifically around this result. It is, at this point, an observation I've made about the data. Our study is for all measure of efficiency measures employed on specific buildings in specific locations.

I would not call myself a Title 24 expert by any measure. My expertise in this area is limited to the study required to model the standard and prototype buildings in the Passive House Planning Package (PHPP), which is the energy modeling software we use for Passive House design. If you private message me, I'll offer you an excellent referral to a suitable consultant.


Here are some facts

Whole house fans preceded air conditioning by decades - example  - a 50 inch fan in a home in Atlanta built in 1903. That size is typically 20,000 CFM.

The average whole house fan today draws about 400 watts and pulls 6,000 CFM. 

The average 10 year old air conditioner for a 2800 SF home draws about 6000 watts. 

Thanks for the input. The next question to ask is "how much cooling power is delivered in each case?" Whole house fans work best when the house is hot and the air is cold. Either of those things change and they work less well. I am not suggesting that they aren't effective in some circumstances, but that they ought be scrutinized. Truly passive measures like shading, moderate thermal mass, a well-insulated shell to keep daytime heat out, and night cooling through windows are my first preference.

The average whole house fan today draws about 400 watts and pulls 6,000 CFM. 

The average 10 year old air conditioner for a 2800 SF home draws about 6000 watts. 

Are implying a whole house fan saves 15x the energy over air conditioning?  

The average fish swims.  Cows go mooooo.  My statements are at least honest don't attempt or pretend to be relevant or connected.  

Did you think this through?  Your implications are full of deceit, I hope that was accidental.  

To Ted Kidd,

You should not be accusing me of deceit. I write only facts that are public knowledge. I am not implying a whole house fan saves 15x energy, I am stating that as a fact. I know. I have the 2800 SF house with air that draws 6000 watts and I have a whole house fan that uses 400 watts. What do you have?

I'm not accusing, I'm asking what you are implying with your numbers.  If you are not implying savings will be 15x, what are you implying?  

What do they mean?  What do you think they mean?  If they are meaningless, why did you present them?  

Useful information is the Coefficient of Performance (COP) of the whole house fan vs. alternatives. The true answer is more complicated than that, since all equipment has a COP "curve" that flattens out as the delta-T between inside and out decreases. This means that the climate and the building in which it is installed is a critical factor. Further, "average" existing equipment is not so useful if we are trying to determine best practices moving forward. This is really a great subject for an in-depth study.

I think it boils down to how well the hatch is insulated and sealed. If the hatch is sealed tight and insulated to the same level as the attic floor then it would work in many climates.

I think the proper way to do it would be to depressurize the attic space or exhaust directly outdoors. I think air quality suffers when a fan is at the attic floor pressurizing the attic. Pressurizing the attic is going to create an air flow from the attic into the house bringing who knows what.  The amount of infiltration will be dependent on how well the attic floor is sealed.

Another concern I have is the whether the money could be better spent elsewhere such as insulating and air sealing the attic floor.  I could see in many situation a fan could be the right thing.

In regards to air quality the more air your fans expells the more that must come in. A person with allergies my not find this  desirable. Then there are safety concerns with open windows.


I have seen these fans in mounted in hall way ceilings, I have a couple of issues with them.

They penetrate the pressure boundary (ceiling) they compromise 2-3 sq feet of insulation value. They might disturb the insulation between installed location to whatever openings out of the attic are present.When these fans run they cause large air-flows and hence pressure difference which can cause problems, sucking in dust and pollen for instance. In homes with these fans I  have never seen  propper pressure relieve in the attic IE an opening between the roof deck and the outside that is at least equal to the fan opening in the ceiling.

If there is no matching pressure relieve you pressurize your attic which might have all kind of unintended consequences for the longevity off the structure.


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