# Summer science: How to cool an apartment with a fan?

So the debate continues in my household-- We can’t be the only ones rehashing this problem every evening.
Problem: It’s 7:30 or so and begins to be cooler outside the apartment than inside.
What to do with the box fan?
(this is all predicated on about 1000 square feet, no AC (of course)).

Conflicting theories/approaches currently under consideration:

a) open the doors and windows and stick the fan in an open door/window directly blowing the cooler air into the space. Rationale: Fast forcing of air into the space, it will figure out where to go.

b) open the doors/windows, and place the fan in one of them blowing the inside, warmer air OUTWARDS. Rationale: flow-through-- causing a current outwards that will indirectly suck cooler air in through the other openings elsewhere in the house.

We have our own pathetic attempts at debunking each others’ approach (I don’t want to reveal which approach/theory is mine for the sake of neutral info gathering-- I’m open to correction)-- anyone have anything meaty to contribute to this problem? Does size of the space matter?

A works somewhat better, as it’s more direct. It’s simple to test this, put the fan into extractor mode then feel if there is a man-made breeze coming in from the other windows. There won’t be.

However, to make supporters of B feel better, a combo of A & B works best. In this case, the two fans need to be at opposite ends to work best.

I’m going to guess here, only going from 17 years of living in an un-air conditioned L.A. apartment.

Putting a fan facing out the window moves a small amount of air behind it. Putting a fan in a window so it blows in moves a larger amount of air in front of it. The moving air mixes the cool and warm air better in the room than the exhaust fan does.

Both would work even better if you can seal off the rest of the door/window that the fan doesn’t cover.

The best answer is: c) purchase a second fan and place one blowing outward, one blowing inward, on opposite sides of the apartment, preferably going with (not against) the prevailing breeze. Exhaust fan should be as high up as possible (since heat rises).

If you are limited to one fan, however, I’d guess it’s better blowing inward than outward. The increased circulation in the room should cool you (especially if you’re in the path of the fan) and the room down quicker. Try to blow from the cool (shady) side of the apartment. The only disadvantage to going inward is that fans themselves create a little bit of heat due to inefficiencies in the motor, but better circulation is more than enough to account for this.

Also, unless there’s a decent amount of breeze outside, you might be better off closing the doors and putting the fans in the window instead, and put cardboard (or whatever) around the outside so air can’t travel through unless it goes through the fan. The intent is to avoid circulation directly around the fan.

The most important thing is to first figure out what the natural airflow through the apartment is. Most of the time, you’ll see consistent wind direction based on time of day. Setting up your fans to encourage this natural flow is going to be the most important part, regardless of whether they blow in or out.

That said, blowing in is slightly better because you can sit in front of it and have the coolest air at the highest speed. I doubt it makes a difference as far as total air flow or overall temperature in the house, but it’s a huge difference for the two feet in front of the fan.

Another trick: put a damp dish towel or washcloth on top of the fan so that the air blows across part of it. You don’t want to obstruct the air flow much, but getting the air to flow over the moist rag creates a mini swamp cooler. I can’t swear that the effect isn’t mostly a placebo, but I think it helps.

I don’t think box fans are all that powerful enough to blow hot air OUT. When (if) the air is cooler outside at night, I’ve had best results putting the box fan in the window of the room I’m in and letting it blast the cooler air into the room for as long as it takes. (A window open in another room, too, for cross ventilation.) I can’t hear the TV while this is happening, but after an hour or so I can put it on ‘low’…

If you want to cool down the overall temperature in the house the quickest, you want to maximize the temperature of the air flow leaving the house, and minimize the temperature coming in. The more heat carried out of the apartment, the quicker the house cools down.

If the box fan is on the floor (usual position for a box fan) and blowing outward, this is sub-optimal because all you’re doing is blowing colder ground-level air outside.

However, if the box fan is pointing inward, the high velocity air is able to circulate and blow across a majority of the room before exiting- this ensures that it picks up quite a lot of heat along the way.

Almost all the value of a fan is the perception of cool caused by moving air over your skin enhancing evaporation.

Blowing in vs. out is not going to matter spit to the actual temp of the room air and room contents. Maybe a 2% advantage for blowing in. Which would be more than offset if that direction was against the prevailing natural breeze.

But having the fan blowing on *you *is going to make *you *feel (and really be), 10%-20% cooler. So do that.

I live right on the coast of Lake Michigan, so that might change things, but an open window in one end of the apartment and a box fan in a window blowing out at the other end keeps me comfortable all summer.

If I’m blowing in, I’m happy in one room, but then I have to move it or have two fans, to be comfortable in the other rooms.

Put fan in window exhausting air. open windows slightly in each room so air is drawn from each room. That is the idea behind a whole house fan. You mount it in the ceiling and draw colder air outside air from all the rooms.

However, the amount of air that can be moved is dependent on the fan so for a small box fan it’s best to sit in front of it while it draws cool air in and blows it direclty on you.