Most efficient fan usage.

In this heat wave we’re having, getting circulating air is very important. Is it more efficient in the evening to have a fan in the window 1) blowing the hot room air out, or 2) blowing the cool outside air in? Assume other open windows for circulation.

Hopefully you’ll get a more expert answer, but my WAG is you should blow cool air in, to create a breeze, which leads, I think, to a greater amount of convection of heat away from the surfaces in your room. (Including the surface of your body, meaning less sweat, which is always a plus.)


Go with the wind and ‘heat rises’ for max ventalation. Fans blowing out on the top floor high up windows and fans blowing in on the lower level windows. This also can be used to blow cool (but usually damp) air from the basement to the upper levels which will cool it down a bit.

If the wind is coming from the north, fans on the north side blow in, and out on the south.

Working with nature is your best shot.

Now sometimes you don’t want to do that. like when you are in a room and want the outside air blown on you. In that case you might have to oppose nature.

Kanicbird has shown you the principles of good cross ventilation. I’ll just add a little. Airflow often takes the path of least resistance. When the wind fades, as it often does in the evening, your mechanical breeze will go between the fan and the nearest other open window, leaving still air in the other rooms.

If you blow air out one or two windows, air will come in somewhere else. You can steer the airflow according to which windows are open.

That’s the best solution in my house. I have one fan blowing air in and one blowing it out. I put the inake fan in my bedroom, and that room cools off the most. The outtake fan is at the opposite end of the house.

Cool (as it were.) I am doing it right. Thanks, everybody.