General Question

Nimis's avatar

On a hot day, which keeps your house cooler?

Asked by Nimis (13088 points ) May 7th, 2012

Which combination will keep your home the coolest?
– shades drawn / windows open
– shades drawn / windows closed
– shades open / windows open

I’m guessing that it’s not:
– shades open / windows closed

What other things factor into this?
– breeze
– height (first floor VS second floor)
– type of shades
– type of windows

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14 Answers

Charles's avatar

– shades drawn / windows open

Of those three choices this will provide the most heat dissipation and wind chill effect and the least radiant heating.

blueiiznh's avatar

On a super hot day 95 and above it almost does not matter. Especially does not matter if the temp doesn’t drop at night to something that will cool it down.
Higher floor – Shade drawn / windows open
Lower floor – Shades drawn / Windows Closed

If it is humid, it just does not matter.
i sit in the pool on those days

john65pennington's avatar

Lets face it, when it’s 95 degrees outside and the humidity is about 60%, nothing is going to keep your house cool. Best bet is to go to four hour movie and watch it twice.

Idea for night time cooling…....

Instead of a window fan blowing air into the room, turn the fan around and turn on high speed. In this manner, the fan will push the cool outside air in a circle, on the outside of your house, and bring in the cool air into each opened window.

JLeslie's avatar

Blocking the sun and letting a breeze through should cool down the house, but if the temperature outside is very hot, sometimes it is cooler not letting the hot air in. Waiting to open windows once the temperature drops in the early morning or evening hours, and then closing everything up during the hottest part of the day can sometimes be the best solution. The breeze will only coming through in a significant way if you have a cross breeze, meaning windows open on both sides of the room.

thorninmud's avatar

It boils down to a simple question: is the air outside hotter or colder than the air inside?

If the air inside is cooler, windows closed; if the air outside is cooler (this crossover point will happen towards evening), windows open. This is where one of those indoor/outdoor thermometers comes in handy.

Air circulation does matter in how hot it feels, but it’s better to get the circulation with a fan than by opening a window to the hot outside air. That breeze may feel good in the short term, but it’s actually just flushing out whatever cooler air remains in the house.

Shades help a lot by controlling radiant heat. That’s a matter of keeping direct sunlight out. Where windows are’t receiving direct sunlight, they’ll slow down convective heat exchange by a little bit, but probably not much.

CWOTUS's avatar

Believe it or not, what keeps my house coolest on a hot day is “shades drawn / windows closed”.

I put new thermal windows on the house a few years ago that really help to keep the indoor temperature regulated (warmer in winter, cooler in summer). And since most of my windows are on the other sides of the house than South, I don’t worry about drawing the blinds.

I’ll generally open the windows late in the evening and run the attic fan to pull in cooler outside air (when it does get cooler outside).

Coloma's avatar

Yes, I go for shades drawn windows closed too, but…on really hot days my house will stay cool til about 2–3 o’clock and then, nothing works except the AC.
This is something I hate when I am working a lot, I don’t want to run the AC all day when I am not home, but coming into a hot house sucks. I usually then open up everything, blow it out with the house fan and other fans then turn on the AC for awhile. Ceiling fans help a lot too.

I installed a new one in my living room last year and it’s got power! :-)

WestRiverrat's avatar

A combination of shades drawn/windows closed when the sun is on those windows, and Shades drawn windows open in the morning before the heat builds, closing the windows when the heat starts to rise. At night shades open windows open to allow free air exchange with the hopefully cooler night air.

@Coloma couldn’t you put the AC on a timer so it starts up about an hour before you get home. I know with my new thermostat I can program the house with different settings and the heat and AC will run at a lower level for most of the time I am gone but kick in so that when I get home it is at the desired room temp.

Coloma's avatar

@WestRiverrat That’s an idea! Hey…I like it! :-D

wundayatta's avatar

Humidity is important. If it’s just hot, then opening the windows and shades seems to work, at least on the shady side of the house.

But during high humdity, we’ll close both shades and windows and turn on the a/c.

DominicX's avatar

I’m assuming we’re talking about non-air conditioner solutions?

In my current apartment, my room gets the most sun, which I do like, but it means my room is several degrees warmer than the rest of the house when it’s hot, even with the air conditioner on (and I won’t set it lower and waste energy). It’s also second-floor, so it’s even hotter. It can 10 degrees warmer in my room than in the living room.

So I typically keep the window closed (if it’s more than 80 degrees outside, guaranteed it’s less inside, so leaving the window open isn’t going to help) and keep the blinds closed (or near-closed…I hate having to use electric light when it’s sunny and nice outside).

That seems to do the job, but unfortunately the windows aren’t like the ones back home that filter sunlight and heat, so the window itself sort of becomes a radiant heater…

At that point I usually just go out to the pool :)

rooeytoo's avatar

The older folks in Australia (those who are of the pre air con age)and remember, we are called the sunburned country always say keep the blinds drawn, shutters and windows closed all day long. When the sun goes down, open up everything that opens and let the cool night air in. I have tried it and it does work better than anything else except air con on 24/7.

I see @CWOTUS advocates the same method. It sounds strange but it does work. I even think it helps to keep the humidity out a little bit.

downtide's avatar

My house is nearly always cooler with shades drawn and windows closed. But it’s an old house and difficult to keep warm.

silky1's avatar

Dark colored shades and windows open work the best for me.

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