How much electricity is my AC unit using when it's on "fan"?

September 28, 2008 9:58 AM

Does my window air conditioner use just as much electricity on the "fan" setting as it does on the "cool" setting?

On cooler days this time of year, I often turn my window AC unit to the "fan" setting to pull in some of that cool air from outside. I have always assumed that if the unit is functioning as a fan, it's not using nearly as much electricity as when I've got it set to "cool." Is that an incorrect assumption? And if it does use less power than when it is cooling, how much less? Is it a negligible difference or is it substantial? Would it be better to just stick a box fan in a window?

posted by amro to work & money (7 comments total)

You're using less power because the compressor is not kicking on, which is what uses most of the power. This page claims the fan motor only consumes 10% of the total power used by the unit, but no idea where that figure came from.
posted by cabingirl at 10:08 AM on September 28

I actually measured a window unit with a wattmeter. I can't recall specific numbers but it drew about 150W when just the fan was running, and about 1000W when the compressor kicked in.
posted by crapmatic at 10:11 AM on September 28

Note however that even though the compressor uses much more power than the fan used to circulate air, the compressor itself only runs intermittently. So "how much more power" is a bit up for grabs - it depends on how cool it's set to, where cooler settings lead to the compressor running more.
posted by drmarcj at 10:49 AM on September 28 [1 favorite]

What they said. Also if your goal is to get outside air inside, the window fan is a much better bet. My window AC unit just recirculates indoor air. If yours does bring in some outside air, its probably not more then 20% or so.
posted by ihadapony at 10:58 AM on September 28

Keep in mind that box fans can use quite a bit of power, and are often not very efficient on the lower speeds. For instance, mine uses 75 watts on a very slow Low and 150 watts on a very good High. It's like leaving an extra incandescent light bulb on for hours at a time.

If you're really interested in this, a Kill-o-watt meter is a great investment.
posted by smackfu at 11:14 AM on September 28

i used a kill-a-watt to find this out...you use about seven times as much energy using the compressor as just the fan.
posted by thinkingwoman at 3:06 PM on September 28

All of your answers were helpful, so I have marked them all "best."
posted by amro at 10:36 AM on September 29