Every winter: 🦝 ah, time to make the annual "Here's how to DIY an anti-SAD lightbox" post
Every summer: 🦝 oho, time to make the annual "Here's how to suck cold air in" post
"Sucking cold air into your house rather than paying for air conditioning," the post that confuses and enrages Americans every year!
Prerequisites: no nearby wildfires, temperatures lower at night, one fan.
Bonus nice-to-have: indoor/outdoor thermometer/hygrometer. Incense (or vapor or a friend who vapes) to visualize airflow.
Method: at night, open two windows; one in the lowest part of the house (unless you have a basement colder than the outside, in which case find the coldest window that's not colder than the outside), one in the highest. Single-storey places, open a window in the coolest room and another in the hottest. Houses with cats, check window screens, replace screen fabric where necessary.
Orient fan in hottest room, one to two metres away from the open window, with airflow facing OUTWARDS. Put the fan on full blast. As the hot air is forcibly exhausted through the open hot-side window, cool night air is drawn in from the open cold-side window.
It might make more intuitive sense to place the fan facing inward in the cold side window, but try it both ways and you'll see how much easier it is to blow hot air out than blow cool air in. The hot air already wants to leave, it wants to expand into the cold night, adding the exhaust fan encourages it.
The optimal placement of the exhaust fan will be different from room to room; it'll always be facing the window and blowing outwards, but you can make a big difference to efficiency by moving it closer to the window or further away. Experiment, using incense or vapor to make airflow visible.
In the morning, close both windows and turn off the fan.
Advanced: check overnight air temp forecast on your weather app, set timer to pull cold air in until just before sunrise or whenever air is coldest.
Edit: this never occurred to me because I don't have an upstairs bathroom; if you have a bathroom upstairs with an extractor fan, experiment to see if that works well enough in place of the fan I've been talking about this whole time
@tehstu take a walk around the neighbourhood at 1am on a cool night sometime and I bet you'll hear dozens of the damn things buzzing away, making a bloody racket and sucking down the electrons
🐰 I have a window fan / box fan, will that work?
🦝 If you can set it so it blows out, sure. It'll work better if you can move it back a bit, but any fan blowing hot out at night when the air is cold outside will outperform air conditioning for a tenth the money, money which by the way goes to some of the dodgiest people on the planet
🐹 It's really humid where I live, should I run my AC?
🦝 For all its popularity in the USA, air conditioning is horrifyingly bad at cooling down humans. However, it's GREAT at dehumidifying the air. Do the fan trick, then run the AC for ten minutes or so first thing in the morning (after closing the windows, and yes I do mean while the house is still cool) to wring the wet outta the air.
🐴 Will a ceiling fan interact negatively with this exhaust-fan trick?
🦝 Ceiling fans are America's greatest invention. As for yours, I've got no idea, but if you usually sleep under a ceiling fan try having your bedroom be the one pulling in cold, you might prefer it.
🦆 Which window should be the cold suck side?
🦝 If you wanna cool down the whole house, choose one that's furthest from the hot blow side. You'll have to experiment.
🐺 Is there a contraption to automate this?
🦝 There's a thing called a "Whole-House Fan," and it's This But Bigger. Have a look on the usual video sites to see them in action and see installation instructions.
🐧 what's the deal with box fans and shrouds?
🦝 Fans made for cooling down humans have different design considerations than fans made for other uses like exhausting fumes or whatever. Sometimes in industrial settings you'll see fans that are obviously made to fit in a square frame, but have a bit of sheet metal with a round cutout about the size of the fan blades. That's the shroud. It's there on the industrial fans (whose job is "Move a lot of air in THIS direction") because without it, the edges of the fan frame will actually suck air in rather than blowing it out. Shrouds are absent on household fans (whose job is "Move a lot of air, don't care where") because we use them to cool ourselves down; it doesn't matter if the air moving over us is travelling in a particular direction, it just matters that we've got air moving over us. But you're gonna use a household fan as though it were an industrial fan here, so if your fan's square then you might consider making a shroud to improve (sometimes nearly double!) its directional airflow. Use a sheet of paper or a tissue to find out where on the box is sucking where it should be blowing, and simply tape over those areas with masking tape (or cut a circle in some cardboard if you feel fancy). The Corsi-Rosenthal box people posted a lot of info in the last few years about fan shrouds, so searching for that might be useful, but don't overthink it and stress about it because you can do the lion's share of the improvements just by adding more tape around the edges until the bit of paper always gets blown rather than sucked on the exhaust side. 90% of improvement will get sloppily slapped on in the first five minutes, and another 5% will take you an hour, and another 2% might take all night, it's that kind of situation, don't sweat it too much.
🦄 Will opening just one window work?
🦝 No, not really.
🐌 Will opening two windows far from each other work, without using a fan?
🦝 eh, kinda. Any multi-level house is basically a chimney and hot air will rise. But adding an exhaust fan will make it go WAY quicker.
🐙 How about one exhaust window and many intake windows?
🦝 Maybe, depends on your house. This is where the incense comes in.
🐫 Why incense and not an anemometer?
🦝 Because you don't have one.
🐫 Oh yes I do.
🦝 Fine, use that, but it won't smell as nice.
Is there any advantage in this set-up to having a high-powered fan right up in the window rather than a few meters back?
I would gladly give up a/c. As it is, we have to use it sometimes when the humidity in the house gets very bad, but I try to use it as little as possible.
@westerling Unless the fan (or a shroud) takes up the whole open part of window, putting the fan right on the windowsill results in some air getting sucked in from outside around the edges of the blades and then blown right back out, so moving it back a bit ensures that it's Hot Room Air that gets sent That Way.
But tbh even if you slap the fan right in the frame it's still way more efficient than AC on a cool night :)
@ifixcoinops Don't want to leave it running all night here. Even on a hot day the nights are usually cool enough to chill things down in an hour or so with the 8000 CFM drum fan I have.
@ifixcoinops I used to do this a lot before wildfire season. Unfortunately the last few years the hottest days have also been combined with a literal forecast of "Toxic Air" and warnings not to open doors/windows/go outside.
Weeeeee.
This does work in my new place just with the two upstairs windows tho! One side of the place is always cooler, one hotter. So I leave both windows open and enjoy a cross breeze upstairs til the temp climbs in the AM.
@ifixcoinops Hi, it’s winter down here 🇳🇿 Can I see the anti-SAD post?
It's also cold if you have a reverse of your summer one, but since the outside daytime air is still Cold, the heatpump and insultation is probably my best bet.
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