Is a whole house fan worth it?
May 1, 2015 2:28 PM   Subscribe

With the summer about to come on strong, we're considering installing a whole house fan in our newly bought house (Los Angeles area). Before we take the plunge, I'd love to hear from anybody who has one, preferably in a climate like ours -- the good, the bad, and the ugly. Worth it or not?

We bought our house a bit over a year ago, just in time for summer... which, indoor heatwise, was just awful. The days got hot, the house heated up, and at night when the air got nice and cool... the house simply stayed hot. We had to either run the air a lot (expensive, and really irritating to do at night when it's nice and cool outside) or just suffer through 85+ degree heat indoors. Mostly we did both.

I'm not willing to go through another summer like that, especially since we now have an infant son to think of. We've fixed a lot of the obvious problems: we installed nice blinds, fixed the hole in the ceiling. Although our attic insulation is crap, we're getting that taken care of. I don't think all this is going to be enough to keep the house cool, though.

I really like the idea of a whole house fan (not to be confused with an attic fan) to expel the hot air and suck in the nice cool air at night. I wish I could use a powerful window fan for this, but our windows are all pretty narrow and I can't find a decent one that will fit. I'm leaning toward getting a decent whole house fan installed, but given the cost, it would be nice to get some input on this before we commit to doing that. I don't personally know anybody who has one, so we're asking the hive. If you have one, do you like it? Do you still have to run the AC much or does it help with that? How do you effectively use one?

Thanks so much!
posted by captainawesome to Home & Garden (25 answers total) 7 users marked this as a favorite
They work really well for cooling the house down at night, as you say. For me, it doesn't replace the AC, because when it's 90 degrees out at 5:00 and it's not going to cool down until 8:30, that's three hours of being in a hothouse. Where I am in Northern California, there's only a handful of nights when it's so warm out that I run the AC overnight. The house fan would be great on nights like that.

All that said, the one that came with the house I'm in is REALLY loud -- like, airplane engine loud. The cord snapped right after we moved in, and the repair guy who replaced it replaced it with a switch that only has a single speed, and that speed is HI. I would use ours much more if I could run it on low, or if it was quieter in general.

I don't know how old ours is since it came with the house, but I suspect it's at least 15 years old. There might be much quieter ones on the market now.

TLDR: Great for nights when it's cooler outside than in. Not really an AC replacement if you spend any time in the house during the hot part of the day. Can be noisy.
posted by mudpuppie at 2:35 PM on May 1, 2015

Valley girl here. We have one and it's great, great, great -- until it's not. It's absolutely genius at doing what you describe: pulling the cool air in at the end of the day. But there comes a point in each summer when that's just not cutting it. It's hot outside and inside and we are all miserable. (And then we turn on the AC, which we have, so.) Also, it's great in conjunction with opening windows, patio door, etc. Just to maximize all possible air movement.
posted by BlahLaLa at 2:40 PM on May 1, 2015 [2 favorites]

Yes, homes I've visited in the area with one were very pleased with it.
posted by tilde at 2:50 PM on May 1, 2015

We had what we called an "attic fan" when I was growing up, and it appears to be exactly the same as a whole house fan (I googled it). We would turn a dial, and it sucked in air from open windows. If this isn't what you're asking about, could you clarify a bit?

My dad was always stingy about using the a/c and swore the fan was just as good. I hated it, because all it did was move the hot air around. Now that I live in a house with decent a/c that I'm not afraid to use, I still sometimes wish I had the old fan. It was excellent at taking care of cooking odors, and would be great during spring/fall when a/c is overkill. It won't replace an a/c (which isn't a concern for you, it sounds like), but is a great supplement in sub-80 degree weather.
posted by masquesoporfavor at 2:51 PM on May 1, 2015

Orange County here. I LOVE mine. LOVE. LOVE. LOVE. If it's cool outside and blazing inside, it's awesome at cooling things down fast. I had it installed about 3 years ago. Worth every penny.

A few things to keep in mind...

1) If you have a two story house, you have to only open windows on the floor you want to cool. So if you have windows open downstairs, the upstairs is not going to get cooled very well. Conversely, if you open just upstairs windows, the downstairs will stay warm. If you open windows on both floors, I find it doesn't do a great job on either floor.

2) Never turn it on without a window open. It will suck from any open airway, which if you have a wood burning fireplace will distribute ashes all over the room.

3) Mine has a remote control instead of having had them put a switch on the wall. It isn't terribly reliable and I end up standing under where I think the unit is in the ceiling and waving my arms wildly in a Stevie Nicks impression trying to get it turn on or off. But maybe I need to replace the batteries...

4) It's not quiet at all. But I choose to consider it loud white noise and focus on how good the air rushing in the window feels. Mine has a high and a low setting and I can't tell the difference. They're both loud!

Attic fans, at least as marketed here, aren't the same thing.
posted by cecic at 3:06 PM on May 1, 2015 [1 favorite]

I grew up in Claremont, which you may know is hotter than the hinges of hell in the summer and fall, and we had a whole house fan that we called an attic fan (I just learned the difference because of your question). I loved it. My bedroom was on the second floor and really heated up during the day, and the fan made an enormous difference and was much more pleasant than air conditioning. It was loud but it was a consistent hum so it never disturbed my sleep.

When my husband and I moved to West Hollywood, we had AC and I really disliked it. It felt wrong, even on the hottest days. I wished for a whole house fan.
posted by janey47 at 3:11 PM on May 1, 2015 [1 favorite]

Response by poster: masquesoporfavor, the terminology gets a bit muddled, but it sounds like you did have a whole house fan -- it exhausts the house air through the attic and outside, and cool air comes in from the windows to replace it. By contrast, an attic fan is mounted in the attic and blows out the hot attic air -- cooling the attic but not the living space beneath (although I gather you do get some benefit from having the attic above be cooler).

Or just read this link, I guess.
posted by captainawesome at 3:19 PM on May 1, 2015 [1 favorite]

Thank you! In that case, yes I do think they're cool. Ha, fan humor.
posted by masquesoporfavor at 3:22 PM on May 1, 2015 [2 favorites]

Insulation in the ceiling may have more impact than you realise. I've recently moved from a house that was very well insulated to one that has more or less no insulation and the difference is huge. On a summer day, if I hold my hand up near the ceiling, I can feel the heat radiating down where, in the old place, the ceiling was cool even on the hottest days. It's nearly impossible to cool the place down - we have an A/C unit but it has to be run constantly to even keep the heat manageable - as soon as you turn it off, you can feel the heat returning.

Consider a combination of better insulation combined with 'whirlybird' vents and, of course, vents to allow air into the attic space. You can vent from the living space into the attic and the whirlybirds will draw air from the house into the attic and out. This may not be quite as effective as a powered fan, but has no running cost and no noise. The insulation is the key, though - insulating the ceiling is, I think, by far the most cost-effective way of cooling a house. It will also help just as much in winter to keep heat in.
posted by dg at 4:04 PM on May 1, 2015 [1 favorite]

Seconding the fan + insulation.

Insulation is where a lot of home builders cut costs, and it's just not something most people think about. You would lose nothing by doubling down on insulation.
posted by Cool Papa Bell at 4:19 PM on May 1, 2015

I'm in the Valley, and we have an attic fan but it is not a whole house fan, and I am seriously considering offering to go in on one with the landlord because the savings on our electric bills would be pretty substantial.

Yes, there will be a handful of days when even the attic fan won't quite cut it, but there were so many days last summer that we ran the A/C all day just to try to get ahead of that bullshit at 4:00pm where the house would shoot up into the 90s and stay there until midnight even when it was 65 or lower outside. It was probably pretty nice up in the attic.

And yes, insulation should be fairly high on your wish list as well.
posted by Lyn Never at 4:46 PM on May 1, 2015 [1 favorite]

For the past 20 years we have had an attic fan that basically functions as a whole house fan; i.e., it is a big roaring mofo of a fan mounted in the attic ceiling, and when we open the hatch to the attic, it sucks all the hot house air up and out in about 20 blissful seconds as the cool night air rushes in every window. We run it as soon as it's cooler outside than inside. The house stays cool all night, then in the morning we draw all the blinds to keep the house cool as long as possible. It does still get hot in the late afternoon, but we just replaced our 50-year-old single pane windows (half of which were painted shut) with energy-efficient ones so I'm hopeful that it won't get quite as hot. I love the fan, so much nicer than being sealed into an air-conditioned house.
posted by HotToddy at 4:51 PM on May 1, 2015 [1 favorite]

We lived on the west side for the better part of a decade, and never had an air conditioner. The house fan was all we ever needed, and it worked brilliantly. We also had friends who lived (much) further inland who would rig up a DIY swamp cooler (a lot like this) and run their house fan to wonderful results during the supr hot/dry santa ana weeks.
posted by late afternoon dreaming hotel at 5:16 PM on May 1, 2015 [2 favorites]

I'm with dg on this, but the answer does depend on how temperate your climate is. If you get remotely cold winters (not in LA, I guess), putting a hole in your ceiling into your attic isn't the best idea, but insulation and proper attic venting (soffits, ridge vent, attic fan) is.
posted by idb at 5:43 PM on May 1, 2015

We're in New England and have a whole house fan, which we love.

Whether or not it has utility depends on how much temperatures tend to drop from day to night. For us, turning it on for even half an hour at night pulls the cool air in. Doing this prior to bed is a delight, or even in the late afternoon in the summer, when temperatures drop.

We also have good ventilation on the bottom floor -- we have a full screen in the front door downstairs and a full screen in the back patio, plus another screen in the back entranceway. Couple that with opening windows and normal screens and there's a big yawning air suck outdoors to inside when we crank up the fan--if it can't pull in great volumes of air from the outside, it's not worth having because it will work hard but just can't pull enough through the straw to cool off the house.

It does, in fact, sound like a jet engine. It's not possible to relax when it's on--at least, not ours. It's a thing you do as an acute measure, not leave the whole house fan on all day.

We love ours. I like that it works with the outside temperature and essentially, all it's asking is that the inside match the outside. Unlike air conditioning, it's not producing an artificial environment.

Also, I like the breeze it kicks up.

Pro-tip. Not an issue for you in LA I expect, but don't leave the fireplace flue open when doing this unless you love ash scattered over your living room.

Live and learn.
posted by A Terrible Llama at 5:45 PM on May 1, 2015 [1 favorite]

Oh I guess I'll add: we have a velcro insulation patch we put over it in the winter so our heat doesn't escape through the roof. We also made a thing that sits on top of it, on the other side, all winter long--so we do actually seal it off in winter and unveiling it in the spring is A Thing.
posted by A Terrible Llama at 5:46 PM on May 1, 2015

This topic is one of my central interests right now, I'm about to move back in after a gut renovation and I am determined to get the ventilation right this time. A few years ago I had an obligation to cool the place for the summer with no AC, (Long story why,) and I found out just how poorly conceived most household HVAC is, and how little cooling air conditioning is needed if you do passive AC right.

The most important thing to consider is Total Air Exchange. You want to hit one or more ON buttons, and then after some period of time know that pretty much all of the inside air has been exchanged for outside air. How long does it take? Between three hours and one hour if you get it right, or never if you don't.

My breakthrough came when I got ahold of a theatrical smoke machine, and I could use that to watch the air flow.

If you can pull hot air en masse out the top, that's the best start. But where is that air coming from? You need a path from an air inlet through the house and out the top. Having another window fan blowing in downstairs somewhere is a good idea. Then small fans placed to steer the path of the air flow through the whole house. Precise aiming of the internal steering fans is important, think of aiming an arrow, one foot off the target is only a tiny adjustment, but a big difference in results.

Especially with the inside fans, low speed can sometimes actually move more air along the path than high speed which might just stir up a big turbulence in one room.

If you can turn the inlet, outlet, and any steering fans on and off from one household automation kit, then that's the best. You can put a timer on it. The tricky part is that especially the inlet window should be opened and closed for use, that part would ideally be automated.

If you can do a full exchange, the cooling effect lasts much longer as cool air escapes from pockets under desks, inside closets, behind couches.

Key point #1, smoke machine testing (or you can use incense sticks and move them around)
Key point #2, have thermometers inside, outside, throughout, and guide yourself by the numbers. (there are many "feels cooler" illusions that can throw you off)
Key point #3 Check an online hourly graph of temperature, often if possible. You will find that the coolest times outdoors, sometimes the only hour below 70F, usually come between 5AM and 8AM. Totally capture the full exchange during that hour and your job is done for the next 24 hrs.
Key point #4, in making adjustments to your air flow, let the current configuration run undisturbed for an hour or so, so it can stabilize, and then make adjustments.
Key point #5, close the windows when it's warmer outside than inside. Rely on thermometers. This will sometimes meet resistance, "Open the window! It's HOT in here!" Be firm on this point, it's hotter out there.

The main point is point #1. When you can see the air flow, you'll be surprised by what it is doing and how, "pointing a fan over there" does not necessarily mean air is going to flow that way. Most important: Observe and adjust.
posted by StickyCarpet at 6:26 PM on May 1, 2015 [6 favorites]

I lived in a bungalow in IL, humid to be sure and we had central air. The upstairs was miserable and we had a whole house fan there (which was a converted attic master bedroom). As soon as I turned the switch, it was heaven. Sometimes I even turned it on when the air conditioning was on, to draw it upstairs. Yes, I know you have to have a window open. Sue me. It was blissfully cool.

The only thing I didn't know was that it had to be oiled or it might burn out. Which did get fixed when that happened. Otherwise, I loved it and thought it was great. Mine had 2 speeds.
posted by Marie Mon Dieu at 6:41 PM on May 1, 2015

Denver resident, and we have the same Hot day / cool night thanks to it being a high desert. We love our whole house fan and use it religiously in the summer. Make sure that it has good clear ventilation in the attic so it only has to minimally suck air out of your rooms, not push through small vents in the attic. We don't even have house A/C, but do have a portable unit in our toddler's room.

We tend to wait until 8 or 9 PM when the air temperature is about even in and out, and just start the air moving. In an hour or two the whole house is pleasantly cooled down for sleeping on all but the worst nights (hot and overcast, trapping heat at ground level)
posted by nickggully at 6:43 PM on May 1, 2015 [1 favorite]

I was also thinking of suggesting a swamp cooler, and would run both of possible :))
posted by jbenben at 6:52 PM on May 1, 2015

The swamp cooler brings up the next level for good Total Air Exchange operations. Swamp coolers work best in low humidity, and they raise the indoor humidity. Above 80% humidity becomes a big factor in comfort.

If you watch online data on temp and humidity, with weeks-out hourly forecast graphs, and you have temp and humidity readings inside your residence, then you can plan for the best Total Air Exchange time based on both humidity and temperature. (I was using for that but they changed that feature, it might require a subscription now or is only available on smartphones.)

Then it becomes a strategy game like Risk, when to give up some cool, humid air for some warmer, dry air. The swamp cooler would fit in to that game, such as if you traded some cool air for dry air before the hot humid front arrives knowing you can seal up and swamp cool the dry air when it gets hot. That might depend on how soon it is going to get dry again outside, if you want to exchange your now warm, wet air for cool, humid air the next night and skip swamp cooling the next day if there's no more dry air coming.
posted by StickyCarpet at 11:13 PM on May 1, 2015

We were instructed with ours to open every window in the house when it's running. I don't know if that is to save the motor, to avoid pulling air through the chimney, or to avoid pulling radon from cracks in the basement. But opening all the windows in the house is a pain. It also makes it less practical at night if you close windows for security.
posted by SandiBeech at 4:46 AM on May 2, 2015

It's almost certainly cost-effective, paying for itself pretty promptly, in increased comfort and reduced (not eliminated) need for AC. Consider a lighter roof color, as well, and maybe landscaping that will reduce sun on the house. Landscaping is along-term project, but the sooner you start ...
posted by theora55 at 10:51 AM on May 2, 2015

This topic extends into a relatively new science, google Hygrodynamics.

If you properly understand and control your air, you can enjoy far-reaching benefits beyond air comfort. You can reduce the need to paint your house, and you can improve the lifespan and performance of the entire building envelope.

You start down that path by becoming aware of the existing wind patterns that your house is embedded in. Expanding on what I said above, if you are venting out the top, look carefully at which downstairs window you use as the inlet. Open the outlet vent, with no fan, and then open downstairs windows on various sides of the house, at different positions. Let the configuration stabilize, then see which window, under normal conditions, is the one that has the largest natural draft volume. This will be determined by the prevailing winds.

You can put some little flags around outside to get a feel for how the wind blows. The overall wind direction is not as important as the way the wind interacts with the shape of your house. The wind will form localized airfoil pressure zones. Wind blowing hard sideways past a window might create a Bernoulli effect partial vacuum that pulls air out of that particular window. Even in high winds there may be still zones in places due to the shape of the house.

The best Hygrodynamic conditions are when the inlet pressure is slightly greater than the outlet capacity. This way the inside of the house has an overall higher pressure than the outside, and in those conditions all moisture and air will be moving on an outward gradient through all of the semi-permeable walls, floors, and roofs. If it's wetter outside, this keeps everything drier than otherwise, prevents rot and mildew, etc. Conversely in the rare case where it's wetter inside you would reverse that, having the vent stronger than the inlet, to pull dry air into the structural elements.

Where I'm staying now by the beach, the winds are strong, but they sometimes change direction. The different prevailing winds change which downstairs window will have the biggest draft if one window is open upstairs. Dramatically. One thing you want to avoid is a natural draft that moves against the path you hope to induce with the fan. That would increase power usage and in the end not be very effective. The fan should just be giving a hand to naturally prevailing flow.

Generally, at the moment when the outside air becomes coolest, there will be an associated convective breeze at the start of the temperature drop. Try to configure your air flow to use that to help the air along. Carefully controlling the fan will almost eliminate the need for AC, likewise careful placement and timing will almost eliminate the need for the fan.

If all of this seems too fussy and complicated, reconsider that thought in light of how interesting it can be to observe the changing natural conditions. Especially if you are the home owner, gaining this knowledge can deepen your ownership experience, and it can be really fascinating when you see what's actually happening and how often it is not what you would have guessed.

The key to this understanding is to have objective data. A wireless temp/humidity system with various inside and outside readings displayed is fun. Little flags are fun too. The smoke machine is fun. If you install a weather station kit, you can connect to a network like weatherunderground and become a crowd sourced node in the public weather picture. This could actually improve their forecasts at your location, and now they have a social network kind of thing around these home stations, which among other things will put your data on their map and you can link from the weather map directly to your business name or web page etc. and get some location-based visibility if that helps in any way.
posted by StickyCarpet at 12:29 PM on May 2, 2015 [2 favorites]

I'm in the Sacramento area, which can have a 60 degree temperature differential in the summer (nothing like going to work when it's 50 degrees out and having to dress for 110 in the afternoon) thanks to the Delta. I have a whole house fan and replaced the insulation in my "attic" a few years ago and summers are much more comfortable now. It never gets above 85 inside, even when it's 110 outside, but like others said, it doesn't replace the A/C. But I have a wall unit in my living room and that and the whole house fan is enough to keep me comfortable through a Sacramento summer.

Also mine is in my laundry room, which is right off the kitchen, so it's handy for sucking out kitchen smells (bacon smells nice when you're cooking it, but not 8-16 hours later) and it's directly above the litter box, so that's useful as well.

You sometimes have to be selective about which windows you open when the fan is on. In the morning I have to be sure that the windows on the east side of the house are closed, and the north and west ones are open. Although really, north windows are usually a good bet in general (unless your neighbors on the north side of your house are assholes who smoke outside because then the smoke stench gets sucked into your house and you end up in a murderous rage...)
posted by elsietheeel at 3:39 PM on May 2, 2015 [1 favorite]

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