Whole-House Fan Strategy?
June 29, 2021 12:45 PM   Subscribe

I don't like AC, mostly, but it's going to keep getting warm, Maine is humid, and I'd like to be more comfortable. My house is small, heats up quickly, cools down slowly. The oak tree will provide shade in 10 years or so. Would a more powerful fan, exhausting air from the 2nd floor, which is mostly eaves, help make it comfortable?

The finished walk-out basement is fairly cool, but if I open a window to allow the stack effect, it lets in a lot of ground-level moisture and seems counter-productive. I do close windows downstairs, open 1 door, and can feel the air moving if I stand on the stairs. Pleasant, but not enough. There's no attic, and no access to whatever tiny crawl-space may exist. If I add a fan to exhaust hot air, what size? How do I assess the air-moving capability? Wattage? I don't think the classic 20 buck box fans are all that strong; I have several and use them for personal cooling. I do close sunny windows and drapes in the morning, it doesn't seem to do much. There's a 1st-floor deck and patio umbrellas to reduce sun.

AC? Lots of people are buying air conditioners for this heat wave. And once installed, one tends to use AC, and it is a significant contributor to Climate Crisis. I love open windows, breezes, and my house is usually fine in summer, but things are changing rather fast. I am aware that AC exists, it's not a good answer to this particular ask.
posted by theora55 to Home & Garden (24 answers total) 5 users marked this as a favorite
Yes, it will help. I don't have details, but just wanted to separately recommend a heat pump- Maine has a rebate program. Heat pumps use the temperature difference underground, and can be used both for heating and cooling.
posted by pinochiette at 12:56 PM on June 29, 2021 [5 favorites]

Awnings. Stopping the sun from coming in your house goes an awfully long way, more than you’d expect. The fans will help.
posted by mhoye at 12:58 PM on June 29, 2021 [7 favorites]

How's the insulation?
posted by aniola at 12:59 PM on June 29, 2021 [3 favorites]

I do close sunny windows and drapes in the morning, it doesn't seem to do much.

What colour is the side of the drapes that faces the windows?

Ideally you want it as close to pure white as you can get, so that as much incoming light as possible bounces straight back out again. Otherwise your drapes and your glazing are just operating as a solar absorption/greenhouse heater and warming the interior air by convection.

External awnings work better than internal sun-blocking drapes because they stop the radiant energy coming in through the window in the first place.
posted by flabdablet at 1:00 PM on June 29, 2021 [5 favorites]

I live in Chicago and my whole house fan works great. I usually use it after the sun goes down and it really helps to bring in cooler evening air. I rarely use my central ac after sunset because of this. I prefer open windows and breezes. Not sure what size it is, it's been here since I moved in. It's in my small rafter/attic, and I turn it on with a switch in my 2nd floor hallway.
posted by j810c at 1:10 PM on June 29, 2021 [3 favorites]

The general principle here is that stopping heat from getting in is almost always easier than getting rid of it once it is in. An exhaust fan will get rid of hot air pooling under the ceiling, but better ceiling insulation coupled with above-ceiling ventilation works better.

If the outside air temperature is high then your house is going to warm up if you draw outside air in by exhausting interior air, unless you cool the incoming before it arrives. Sometimes it's practical to do that by pulling it through vent pipes buried in the ground for some distance, either under the house or on its shady side; even as little as a metre below the surface, ground temperatures are usually far lower than summer air temperatures.

Paulownia trees are very fast-growing and provide beautiful leafy shade many years faster than oak trees can.
posted by flabdablet at 1:13 PM on June 29, 2021 [5 favorites]

Best answer: +1 to Heat Pump, and +1 to awnings or any other method to block shade (trees).

I don't think an exhaust fan would do as much work as you'd think. If it's hot outside, the hot air inside won't be THAT much hotter than outside. And with proper attic insulation, the hot crawl space is heating your house a bit less than you'd think.

If you stick with fans, the larger the diameter of the fan, the quieter AND the more air is moved. I recommend a nice, big, slow ceiling fan that really moves air around!
posted by bbqturtle at 1:25 PM on June 29, 2021

Best answer: I just bought one of the only two real models of window-mounted whole house fans - the Air King 9166, which is a 1/6HP 20" fan (the housing is closer to 27", it is a lorge boi), and the 9155 which is 1/16HP 16" fan (still though, it's 26x22 so the housing is only modestly smaller).

The 9166 RPM (High/Med/Low) is 1600 / 1450 / 1100, CFM (cubic feet per minute) is 3560, 3120 and 2510. That's how airflow is measured.

The 9155 has CFM of 2470 / 1700 / 1360, so even High is slower than Low on the 9166. Reviews say it's fine for a small house or apartment, but I think you'd want the larger fan for a two-story house. (I can't find the RPM listed on the 9155.)

Both models mount on the sill in front of the window, so that the window can be closed behind it. That way you can cool down the house in 20-30 minutes of running the fan, and then close the windows and blinds during the heat of the day.

Even though I used a tape measure before ordering, I still did not anticipate how incredibly huge the 9166 is, and we've only tested it briefly because it arrived right when it wasn't cooling down a ton at night and I still need to actually secure it in the window, but it for sure moves air. It's quite loud, but it is enthusiastic.

This only does you any good if it gets significantly cooler outside than in, and it does not solve your humidity problem. My understanding is that Whole House Fans are much more useful in dry climates than wet.
posted by Lyn Never at 1:30 PM on June 29, 2021 [3 favorites]

(If shade trees are part of the plan, please choose native species. Paulownia is invasive and will not support wildlife the way an oak will.)
posted by Press Butt.on to Check at 1:33 PM on June 29, 2021 [6 favorites]

Just remember that any kind of fan, whole-house or box, pulling air in from outside also means you're pulling in humidity, allergens, and dust/dirt.

One solution I've done in smaller places (and where I didn't want to run A/C) was to close every window in the place except two: one in the bedroom near my bed and a second in different room. The box fan goes in the remote room and blows air outward. This creates a small quiet breeze coming into the bedroom and gets you through the night.
posted by JoeZydeco at 1:35 PM on June 29, 2021 [3 favorites]

Best answer: We have a whole house fan here in humid Chicago. It does indeed cool the house down quickly on those rare evenings when it cools down a lot outside. But we pay the next day, because it draws in all the humid air which becomes a sticky mess once it warms up again.

We’ve been much happier since getting a very efficient mini-split A/C. It’s so efficient it doesn’t seem to affect our electricity usage much. (A tiny fraction of what our window units used to consume!) And the house is now just… comfortable. All the time.
posted by wyzewoman at 2:02 PM on June 29, 2021 [5 favorites]

Best answer: I used an Air King 9166, same as Lyn Never, to clear hot air out of a house we lived in once. It worked great, with the caveat that we were in an area with low humidity that would cool down as soon as the sun went down. The only downside is that it was loud as hell in the room we installed it in, as it does move a ton of air.
posted by zsazsa at 2:04 PM on June 29, 2021 [1 favorite]

Years ago my uncle, who lived just across the DC line in MD in a simple Cape house, figured out a system: he left the door to the basement open, closed all the windows on the ground floor, and then had fans in windows at both ends of the upstairs, one blowing in and one blowing out. It did keep the house pretty cool in a super-hot and humid climate.
posted by mareli at 2:05 PM on June 29, 2021

Do you have shutters, or could you add them?
posted by benbenson at 3:14 PM on June 29, 2021

How about a dehumidifier? They are pretty cheap if you don't need a huge capacity. AC itself also dehumidifies,but you said you don't want AC.
posted by kschang at 4:31 PM on June 29, 2021 [1 favorite]

A deciduous vine, even a thug like hops Humulus, would take a lot of heat out by shading the wall. Will work way faster than your oak.
posted by unearthed at 5:00 PM on June 29, 2021 [1 favorite]

Dehumidifiers are literally A/C units which vent their heat inside, just buy a regular unit. A/C are also heat pumps by definition. Ground source heat pumps are only marginally more efficient than air-source but cost tens of thousands more and may not be more efficient if you count the power draw of the circulation pumps.

With that out of the way...

Pulling in more air will pull in more moisture, but it's the only way to cool down without heat pumps. So the best investment will be keeping your house from heating up. Add large shade cloths between your house and the sun’s position from 11-3, put reflective panels in the windows, ensure your attic has good ventilation (measure the air temperature up there over the day, the higher the amount the higher ROI on additional ventilation,) and use a fan on yourself to stay cool. Obviously some of these things are cheaper or easier to stay with, but combined will significantly reduce the amount of heat you need to remove at night and reduce how hot the building gets during the day.

I can be comfortable with elevated, humid house temperatures during the day so long as I can sleep comfortably. My compromise is on hot nights I run an A/C unit. My bedroom is small and it doesn't run much. The rest of the house is cooled by fans cycling cool outside air through the house. A whole house fan can be useful for this, but they are usually really loud and leak a lot of hot air in the winter.

Finally, check how much energy you use in the winter. I bet it's 5x what someone in Miami would use for cooling year round. If it's the Climate Crisis that worries you, you need a net-zero home. Insulation upgrades, Solar panels plus heat pump will get you heating and cooling and the only way to stop contributing to climate change in your housing.
posted by flimflam at 8:36 PM on June 29, 2021 [1 favorite]

How's the insulation?

yup, my new place is great in every way except there's one alcove that, for whatever reason, isn't insulated, and coping with it in the current HEAT has been a major pain. If it was a discrete room, I could just shut the door. But it isn't, so it's a pile of work daily to isolate that part of my place.

Somebody cheaped out years ago and now I'm paying for it.
posted by philip-random at 8:55 PM on June 29, 2021

Best answer: Came to sing the virtues of whole house fans and insulation and I see I late to the party :)

In my experience of living with whole house fans yep, they're loud as hell, but you run them for only 20m at a time! Open everything up early am or late night or both, run the fan, close it all up.

It's a great accessory to other heat mitigations - used with AC it lets you start with the lowest temp possible (if at some point its cooler outside) and delay turning on AC or avoid it for all but the worst days, etc.

I live in the PNW and was just shopping whole house fans last night because even if it's humid, even if it's smoke season, even if it's record-breakimg heat, if there's even an hour where you have good air quality and or it's cooler outside, that let's you take advantage of it.

And I'm with you - I hate the feeling of the whole house closed up tight :(
posted by esoteric things at 9:53 PM on June 29, 2021 [2 favorites]

A deciduous vine, even a thug like hops Humulus, would take a lot of heat out by shading the wall

and not only will it cool the wall by shading it, it will also cool it by transpiring right next to it, even in humid conditions. Vines are fantastic.
posted by flabdablet at 4:00 AM on June 30, 2021

and not only will it cool the wall by shading it, it will also cool it by transpiring right next to it, even in humid conditions. Vines are fantastic.

Depending on the type of siding you have on your house, it will also destroy your siding, bring loads of bugs, and grow around everywhere you don't want it. If you house isn't literally made of stone, vines are terrible.
posted by The_Vegetables at 8:54 AM on June 30, 2021 [1 favorite]

Response by poster: Many suggestions are longer-term or require an installer. Builders are super busy and hard to find right now.
Awnings would be a difficult install, and a maintenance hassle; they collect snow and most people in New England don't use them because they have to be taken down in winter.
De-humidifiers use a lot of electricity; I use one in the basement to keep it mold-free.
The oak tree is @ 10 years old, planted by squirrels, so, local. I don't own the land to the south so I'm lucky it's coming on. There are other trees providing some high shade. Planting hops not an option.
The insulation is not great, but I did have an audit and it's not terrible, either.
Most of most summers, I'm fine; temps in the 80s are very manageable.
Heat pumps; on my list for longer-term solution, no chance to get one installed soon.
Thanks for answers that directly address the question of fans. Lynn Never, thanks for specifics.
posted by theora55 at 11:43 AM on June 30, 2021

Side note for short-term/immediate relief: do you close up your house in the morning (close windows and shades) to keep daytime heat from getting in (and then open everything up when it cools off in the evening)? Makes houseplants a bit unhappy, but, as others have said above, not letting your indoor air get hot in the first place is way easier than trying to cool it down afterwards.
posted by eviemath at 8:13 AM on July 1, 2021

Paulownia trees are very fast-growing and provide beautiful leafy shade many years faster than oak trees can.

It sounds like you’re not looking to plant a tree, but please don’t plant Pauwlonia tomentosa, which is invasive in other states and likely to be problematic in Maine as well.
posted by musicinmybrain at 1:30 PM on July 3, 2021

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