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Thread: Ceiling fans in Winter -- Weird Physics?

  1. #1
    Technical Fellow
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    Ceiling fans in Winter -- Weird Physics?

    Hi All,

    For a long time we have always run the ceiling fans on slow speed and backwards (flow upwards) for Winter to stir up the air as it seemed to me to make sense. We have electric baseboard heaters that are manually controlled per room with a rotary thermostat. We have 6" walls, double glazing, thick drapes etc.

    Over the weekend with it being so cold, (high of 12F Brrrrrrr) I decided to do some testing and I found that running the ceiling fan in a room actually took longer for the room to come up to a comfortable temperature. Coming into a cold room (cold for 24 hours at least) and using an infrared spot thermometer I took temps on walls and ceiling at ten-spots around the room. That room has a 1000-Watt baseboard heater.

    Running the fan it took 2-1/2-hours to come up from 48F to 72F with a max of +/-1F deviation.

    Without the fan it took 1-hour 40-minutes fr the same result.

    That surprised me, so I am now guessing the fan stirs up the air so well that it evenly heats every tiny part of the room, walls and ceiling. Without the fan, it just heats most of the livable space leaving corners nooks and crannies to warm up over longer time. I didn't think to measure right into the corners of the ceiling and floor etc.

    It seems for years we have been wasting power with the baseboards by running the ceiling fans.

    Any thoughts on this?

  2. #2
    Administrator Kelly Bramble's Avatar
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    Interesting, I suspect that what you are seeing is a more even heating of the room. This is caused by the air being circulated and the subsequent heat transfer between the air and surrounding walls.

    During the hot summer, the fan circulating the air helps you feel cooler because of the increased heat transfer between your body and the circulating air...


    ~ I think...

  3. #3
    Lead Engineer RWOLFEJR's Avatar
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    Try the same test but check the floor at the center of the room and maybe something like a coffee table etc. in mid room and see what happens?? I'd guess it'd take longer to reach temp at the middle of the room without the circulation. With the heat source at the base of the walls it's probably giving you skewed results... sort of. Yes on the walls and ceiling but maybe no in the center of the room? Then there's the insulation factor on a cold day that has to effect the time to temp for circulated vs. not with the source at the base of the walls.

    Myself... I run my fan all summer when the air is on and then in the winter only run it when it calls for heat. Also need to be sure you blow heat in your basement if you have one... whether you hang out there or not. Turns your floor into a big heat sink and keeps cycle times down.

    I don't like the drafty feel of a fan blowing as the temp gets close to calling for heat. Many years ago lived in a place with a heat pump for a while. I hated it... always had that drafty chill spell in the cycles.

  4. #4
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    Summer time I like the fans just fine, even though I still use them on Low so they just stir the air. I, like Bob, do not like the air blowing on me. The speed they go on Low does not make for much of a draft in either Season.

    Bob, intersting comment on the coffee table. Great minds... Last night I did just that, took a temp of the center of the coffee table close to the middle of the room. It lagged behind the wall and ceiling temps by no more than 1F. So, even with the fan off, the warmed air was getting pretty good circulation, saving us 50-minutes @ 1000-Watts. The savings would be more in the living area where there are two 1500-Watt baseboard heaters and two ceiling fans.

    I guess if I did 100 data points I would see the more even warming of the room that Kelly suggests. Too lazy for that though. Inquiring minds do not need to know that much detail.

    Suffice to say, no fans in Winter any more. Kicking myself for not thinking of this ten years back when we moved in. Back then the first thing I did was replace all incandescent with folded fluros, but did not think about the heaters and fans. Ahhhh, assumptions again!!

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