I can’t count the number of times I have walked past a neighbor’s home and seen the porch ceiling fans running with no one there to appreciate them. All the fans are doing is wasting electricity and contributing a little heat to the outdoor air. I am tempted (although I have never acted on the impulse) to pull the chains and turn the fans off or leave the neighbors a note.
Now, leaving porch fans on is bad, but nowhere near as bad as doing it indoors, especially in the summer. I am surprised at how few people understand the basic concept of fans — that they make you feel cool due to the movement of air across your skin. The same way a breeze cools you off, a ceiling fan can make you feel cooler, but only if you are close enough to it to feel the air blowing on you. If you can’t feel it, it isn’t doing any good.
What about circulating the air?
When I tell (or maybe more accurately, annoy) people about this concept, many of them tell me that it helps circulate the air around the room and keeps the house more comfortable. Unfortunately, most of them are wrong.
There are very few situations where moving air around a house in the summer like this improves comfort. If there happens to be a big temperature difference between the floor and ceiling due to poor air sealing and insulation, it might be useful to run a fan in reverse in the winter to bring warm air down, but that’s not what most people are doing.
On a related subject, I have been in homes where people are using their ceiling fans in the summer but they are running in reverse, moving air up instead of down. I once changed the fan direction for a friend and to his amazement, he actually felt cooler with the fan blowing towards instead of away from him.
Ceiling fans increase energy use
A 1996 study in Florida determined that using ceiling fans appropriately could allow people to raise the temperature inside by 2°F, resulting in about a 14% annual cooling energy savings.
The same study found that most people do not adjust their thermostats when using ceiling fans, actually increasing their energy use rather than reducing it.
Those fan motors are hot
Most people can understand that running a fan when no one is in the room wastes electricity, but the dirty little secret is how much heat they put out when running.
I always knew this, but I was inspecting some very well built affordable LEED homes recently, and one of my associates had an infrared camera with him. Scanning walls and ceilings showed that the homes were very well insulated and air sealed, but when the camera caught the running ceiling fan there was a huge hot spot at the motor. The temperature of the motor was far higher than anything else in the room, including windows exposed to direct sunlight.
When the IR image was calibrated, we figured out that the fan motor was running at over 100°F. So not only is the fan not cooling the people who aren’t in the room, it’s also working as a little space heater — just the thing you need for a hot summer day.
There is hope
Now I am not suggesting that we should not use ceiling fans — just that they shouldn’t be on if no one is in the room. If people only use them when necessary and set their thermostat a bit higher, then the extra heat is a small price to pay for the comfort and energy savings.
When selecting a ceiling fan, look at the efficiency of the fan, usually expressed in CFM per watt. The Energy Star website has a list of all labeled ceiling fans in a downloadable Excel spreadsheet that you can sort by efficiency. The most efficient fan on the list is the Haiku by Big Ass Fans.
I managed to get an IR image of one of the company’s fans as well, and, lo and behold, the temperature of the fan’s motor at high speed is only about 81°F. If (like me) you keep your house in the high 70s to low 80s, a fan motor like this won’t make much of a difference at all.
You don’t need to spend a fortune on a ceiling fan. There are many efficient models that are reasonably priced, and there is no reason to get rid of those that are working just fine. You should, however, only use them when they will keep you cool, and raise your thermostat when you do.