View Full Version : Ceiling Fans with AC
08-05-2009, 10:54 PM
We have ceiling fans in our main living area which has ~18' cathedral ceiling. This was a "leftover" from before the new system with "circ" and the heat pump. In the winter leaving the system set to "circ" (and "on" at night) works great for maintaining an even temp. With the AC the upstairs bedrooms run 3-4 degrees warmer. Turning on the ceiling fans, if the doors are left open reduces that to 1-2 degrees. At this point, until we can add some upstairs returns, that's the only option. However, I've noticed that downstairs it's sometimes more comfortable to have the temp set at say 74 with the fans running on low than 72 without the fans. Not a surprise that the breeze makes you feel cooler but for the same level of comfort is it more efficient energy wise to turn down the tstat 2-4 degrees or to leave it warmer and run the fans?
08-05-2009, 11:15 PM
I would imagine the fan costs less to run than a 3(?) ton AC condenser.
08-06-2009, 12:34 AM
It depends on insulation and the size of the home. It may not take a lot of electricity to cool a smaller well insulated home by two degrees. In that case the fan might cost more than AC, especially since the fan tends to run constant while the AC will cycle. That may be even more the case when the weather is mild.
If you were talking five degrees or more it would be easier to favor the fan. As it is I doubt anyone can answer with certainty.
08-06-2009, 12:43 AM
i would say the fan uses less power than a compressor
concerning circ and fan "on". Good for helping to even out temps in witner, but I recomend fan in auto in summer
08-06-2009, 12:52 AM
does air like to travel at right angles . . . or not ? ? ?
08-06-2009, 01:47 AM
I'm sure the fans (there are two) use less energy than the compressor but it's not a question of fan or AC. The AC is running but it will run less if I up the set temperature. If sounds like it's a wash or the edge might go to the fans and higher set temperature. I'm thinking it comes down to comfort and since the fans really help the upstairs and the downstairs main living area is just as comfy (maybe more so) I guess we'll keep going with the ceiling fans. I was just concerned that they might be energy pigs and I was being foolish not to just crank up the AC. Mmm, maybe the ceiling fans can be retrofit with ECM motors :D
Because of the unique challenge of the loft bedrooms at each end of the house we switch to "on" in the summer where we can get by with "circ" in the winter. Except at night in the winter we set it to "on" mostly just because it makes for "fresher" air in the bedrooms. Little if any difference in temperature distribution but noticeable increase in comfort. Likewise on the weekday morning setting set the fan to "auto" in the winter to avoid blowing a "breeze" on winter mornings when getting ready to go to work.
08-06-2009, 02:07 AM
Why not do a simple test, run the Ac with no ceiling fans running for a month and then run the Ac higher set point and ceiling fans and see what is cheaper.
Myself I run my blower fan in low speed and leave the AC run normal mode, and I turn the ceiling fans off until we hit the shoulder season then I will run the ceiling fans on a regular basis. I also will turn the blower fan off when the RH get's too high outdoors to keep and maintain my RH indoors.
08-06-2009, 03:15 AM
The weather in Seattle is far to variable for a month long test to mean anything. Especially since turning on the ceiling fans is a manual operation and would depend on who's home when and what not. I suppose I could shut of the AC and track numbers at the meter with the fans running for a day (have to even out the other electric loads like refrigerators and such) and with them off. Then try and leave the fans off for a couple of days that are close in temperature and leave the AC at 70 for one run and then 73 to get some data. I suspect the conclusion would be about what I've heard here, do what feels comfortable and it's going to be the same cost or cheaper.
08-06-2009, 07:51 AM
does air like to travel at right angles . . . or not ? ? ?
does massive solar heat transfer in through a roof at night or not?
does having rh 5 to 10 points lower feel cooler or not?
08-06-2009, 08:06 AM
I've gotten frugal this summer. Moved the thermostat to 80F and been running a box fan that blows across living room and into the breakfast area. We also have ceiling fans in the living room and bedrooms.
R/H stays between 45 and 50%.
Utility bills are running 2/3 of last summer and we are still comfortable.
Moral of the story: the less the compressor runs....the less the electric meter spins.
08-06-2009, 09:46 AM
Ceiling fans use very little power relative to AC. If you are looking to optimize for economy, set the AC to a temperature that is just a bit uncomfortable on the warm side. Then use a ceiling fan in whatever room you are utilizing at the time. This allows you to localize your comfort instead of trying to make the whole house comfortable all the time. When you leave the room, you turn off the fan and turn the fan on in the room you have moved to. Do not leave fans running when not in the room because they do actually heat the air over time and will add to the cooling load if left on 24/7.
Ceiling fans can make the air feel up to 3 degrees cooler. When utilized properly, ceiling fans can lead to significant savings on electric bills.
08-06-2009, 07:13 PM
Thanks, that's good to know. Pretty much in line with what we've experienced; can comfortably bump the temperature up two degrees when running the fans. We do leave them running even when unoccupied because of the issue with heat and ventilation in the upstairs loft bedrooms. I was wondering about the heat load generated by the fan motors but if the draw is fairly low and they're doing a good deal of mechanical work it's well worth it. Especially since if we keep the main floor living space at 74 the upstairs is going to be ~76 with the fans running and more like 78 or more with them off. If they get that warm during the day there's just no way to get them cool enough at night (Seattlites are wimps when it comes to heat :o )
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