Whole House Fans: Do They Work? Are They Safe? Do They Save Money?

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Summer reminds us every year that our homes can get hot and uncomfortable. Air conditioning is expensive to buy and expensive to operate, using a ton of electricity. HVAC is typically the biggest user of energy in the average home. AC is also unhealthy. Just think of all those dust particles, allergens, VOCs, chemicals, and other in-home pollutants circulating again and again in your home. Every time you flush a #2, for instance, literal particles of poo are sent airborne (so close the toilet seat to reduce that, first and foremost!). Some of those particles settle on your bathroom surfaces, while others stay in the air until they are taken care of by filters (assuming you remember to clean or change them regularly, which most people don’t). But others, like the toxic indoor air chemical pollutants off-gassing from your paint, drywall, carpet, furniture and more, are not typically captured by filters but rather just stay and accumulate in your indoor air.

Whole House Fans For The Win

Whole house fans are a great AC alternative. The idea of a whole house fan is that it pulls air from any open window, and blasts hot air out, through the attic and roof. It’s simple in theory. The fan, properly placed, can pull air from windows throughout the house, as it is typically a very high powered motor (400 watts, according to my watt meter, about the same as 7 incandescent light bulbs). This is best used right around dusk, when temperatures drop as day turns into night time. Any room you don’t need cooled (unused rooms), you can keep the windows closed while the fan is on, which makes its suction power even better for those windows that are open.

The image at the top shows what a whole house fan looks like. The ducting and fan are in the attic, and the only thing you see in the home is the vent on the right there. There’s a flap inside that is closed to keep hot attic air from getting into your home, and when the fan is turned on, the flap opens from the suction and air starts to flow up and out.

How Long Do You Have To Run A Whole House Fan?

The answer to this question, of course, depends on the size of your home, and the number of rooms you’re trying to cool.

In my experience, running a whole house fan for an hour every night before going to bed cools the sleeping spaces in my home pretty well. On particularly hot days, I’ll set the timer for 2 hours. But in practical terms, it’s usually an hour, which is very efficient. Using 400 watts, it translates into 400 watts x 1 hour x 30 nights = 12 kilowatt hours per month. That’s about half a cup of mediocre coffee per month in cost for the average electricity rate in the US, compared to about $45 a month (15 cups of mediocre coffee) for a central AC, meaning a whole house fan can save you over $500 a year AND remove poo particles from your indoor air.

Additional benefits include a lot less maintenance (no filters to change, only one moving part, etc), no need for expensive AC repair and maintenance folks, and less chemicals.

What About In The Winter?

It’s a beautiful thing — the whole house fan works in the winter, too, though obviously less than in the summer. Anytime the temp outside is more desirable than the temp inside, turn that thing on. So in the winter, in the middle of the day, you can ventilate your house when it’s relatively warm outside, and have all the fresh air (a rarity in winter). The whole house fan is just a tool you can use, and if you use it well, it can cut bills and improve your home’s indoor air quality.

When Does A Whole House Fan Not Make Sense?

A whole house fan does have its limits. If you live by a freeway or a coal plant, you might have a lot of particulate pollution in the air around your home. There is no filter on the whole house fan. It will bring in whatever is outside. In this case, it might cool your home, but it might also bring in some toxic stuff.

The other reason a whole house fan wouldn’t work is in places like South Florida, where the outside air temp often doesn’t really drop that much at night. I spent some time in Fort Lauderdale, and dear lord, that place is sticky hot. Night time temps may fluctuate very little:

Some wonder about mold, and hypothetically, if your home is very humid, venting that humidity into the attic, especially if your installer doesn’t put a big enough vent in the attic eave, *could* increase the chance of mold? It hardly is worth mentioning, as after a search, I found no real evidence, but there are forums and blogs where people posit the possibility. (Are those people just trolls from the AC-industrial complex? haha). Who knows, but a lack of compelling evidence means it’s not likely a problem in any real way.

Also, as we continue to find more reasons that natural gas was a fool’s errand, the other caveat with whole house fans is that they don’t play nice with fireplaces, gas furnaces, or other gas appliances. Pilot lights, backdrafts, and smoke/ash from fireplaces would be a concern with the whole house fan. Ask a pro if you have any of these prior to installing. And for the love of Planet A, get rid of your gas appliances asap, electrify things, do energy efficiency first, and then zero out with solar.