Question

Does using a ceiling fan save money while the air conditioner is running?

Asked by Robin Lamb
Levittown, NY

How much money can I save?

Answer

David Bergman

Answered by David Bergman

New York, NY

David Bergman Architect

July 12, 2012

There’s nothing worse – well , yeah, of course there are worse things, but it may not seem like it this time of year – than sitting in a hot, stifling space with no air moving.

And it’s not just our imaginations; that moving air does make us feel palpably cooler.

Save 4-8% on cooling costs

This means that if the air in a room is moving, you can set the air conditioner temperature several degrees higher and still feel just as cool. The big catch here is that, if you don’t adjust the a.c. temp up, then all you are doing is adding the electrical usage of the fan to your bill.

  • With a ceiling fan on, you should be able to raise the temperature setting on your AC by up to 4 degrees. 
  • A typical fan might use 15 to 100 watts depending on the speed it is set to. 
  • A typical air conditioner might use anywhere from less than a 1000 watts (for a small window unit) to more than 5000 for a central system. 
  • So combining fan usage with the AC, you can save 4% - 8% of your cooling costs.

A couple of additional notes:

  • Fans are useful, but only when someone is in the room. They don’t actually lower the temperature; they cause it to feel lower. So if no one is there to feel it, the fan is just wasting energy. 
  • More anecdotally, we only recently figured out that the ceiling fan directly in front of our window unit was apparently stifling the air flow. The downward push from the fan was inhibiting the AC unit’s ability to push the air across the room. At least that’s our theory.

At the moment, I’m sitting at my desk with a window unit about 18’ feet away and small desk fan blowing on me as well. Without the desk fan, I’d probably have to set the a.c. temp several degrees lower.

Remotely monitoring and controlling my AC

On a related note, we’re trying out a ThinkEco “Modlet” supplied to us under a program by our local utility (Con Ed). The system consists of a receiver that the air conditioner plugs into before plugging into the wall outlet, a USB transmitter plugged into any nearby computer with Internet access, and a remote control thermostat. This enables a few things.

  • First, I can monitor the energy usage and cost of the air conditioner from my desktop.
  • Second, the remote control senses the temperature where I need it, not  just at the air conditioner. So I keep it where we sit most often.
  • Thirdly, when there is a peak usage alert, Con Ed – with my permission – can raise the temperature setting a degree or two.

When we first went to set up the Modlet, we had major problems and finally deduced that it was because our ten-year old window unit wasn’t working properly. Off we went to buy a replacement at 9:00 pm during the recent heat wave. 

The new unit, as measured by my Kill A Watt meter uses less than half the energy (because the old one was over-revving to try to compensate) – and actually cools the room.

We might have continued to try to use the failed unit if we hadn’t gone through the exercise of installing the Modlet.

 

For more information:

Read "I have heard it is most efficient to run the fan constantly for a central air-conditioning unit. Is that correct?" a Q&A answered by Hamid Kashani.

Tagged In: heating cooling

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