Well, it’s starting to get hot here in Dixie and with energy prices the way they are I’m looking for cheaper ways to keep cool. I have one of those reversible window fans. I keep it set to fresh air at night when it’s cooler outside and during the day I reverse it and vent the stale air outside. The house still warms up. I would say “toasty” but only if you are used to warm soggy toast. So what is the best way to use the window fan to keep cool (or at least cooler than outside temps)? Should I just give in and turn on the ac? How much more energy is my ac going to use?
I wouldn’t run the fan during the day at all, if I were you, but that’s just my opinion. You say you’re venting the stale air to the outside, but at the same time hot air from outside is coming in to replace it, through other open windows, open doors, or even small cracks that you can’t close. This is because the air pressure inside and outside has to be the same. If that’s what you want, then fine. Some people are willing to pay this price to avoid stagnant air.
I don’t think that there’s one right answer to this question, but I’ll tell you what I do. In the evening when it starts to feel cooler outside than inside I run the window fan to force the hot air out (to be replaced with cool outdoor air coming in through other windows). Early in the morning when the outside temperature starts to rise, I close all the doors and windows to trap the cool air, and leave them closed until it gets cool in the evening. This method works best if you have trees, drapes, awnings, or shutters to keep the sun from heating up the house too fast. The price I pay for this method is that the air gets a little stale (or sometimes a lot stale), and that you can’t catch a cooling breeze.
An air conditioner uses a lot more energy than a window fan. According to this site a window fan uses 200 Watts and a window air conditioner uses 900 Watts. If those figures are right, running the fan ten hours a day for thirty days uses 60 kilowatt-hours and running the A/C the same number of hours uses 270 kilowatt-hours, respectively.
We used the same method, slightly improved, when I was growing up in Saskatchewan. The improvement came from having a basement - sometime in the afternoon, when it would start getting too hot, we’d turn on the furnace fan to bring cool air up through the vents. We could keep the the house at least ten degrees cooler inside.