At my old house, we replaced the HVAC with a high efficiency unit that came with a thermostat that would blow, say, 50% to 70% of the time for air movement to increase comfort level. I'm not sure but I think I recall that it was a variable speed fan that did that for a milder air flow.

My son just bought his first house and installed a programmable thermostat that allows him to do the same thing so I suggested he let the main blower run 50% of the time to see if it increases comfort of the house.

My question is whether there are any issues with letting the main blower do that as far as wear and tear on it. He seems to think the house feels more comfortable and that the AC hasn't needed to kick on. My only other issue with the idea is the main blower is noisier than the one in my high efficiency unit.

Is there any cause for concern with this?

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    Why do you think a continuous air flow improves comfort? you're not getting any air exchange, you know. If you just like a draft, how about a standing fan in the room instead? – Carl Witthoft May 20 '16 at 12:00
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    @CarlWitthoft 1) It's a feature advertised by Westinghouse, Carrier and Bryant 2) I noticed it felt better at my house when we had it and 3) my son says he notices it, too. – Rob May 20 '16 at 14:20

Continuous fan operation equalizes temperature and humidity between different areas of the home, and particularly between levels (where convection results in higher upstairs temperatures). It's also the case that even minor airflow helps a person feel cooler by enhancing evaporation on the skin. It's a good practice to reduce cooling costs because the compressor won't need to run as much for a given comfort level.

Sure, there's some wear to the fan bearings incurred, but fan startup is hard on the fan, so there's benefit from fewer startup cycles as well. I don't see how fan speed is particularly important except with respect to noise, should that be a concern.

  • Start up is hard on the fan? I know there is inrush current, but I am unfamiliar with wear. Could you provide a reference or two, please? – donjuedo Jul 19 '16 at 21:03
  • I don't have any references. It stands to reason that electric motors in constant-load applications typically draw the most current at startup, at which time heat cycling and other detrimental effects are at their worst. If you've ever heard a table saw fire up you'll get what I'm saying. You can almost hear the arcing and strain. – isherwood Jul 19 '16 at 21:06
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    Ok, here's one: en.wikipedia.org/wiki/Motor_soft_starter A soft-starter is presumably designed to counter exactly this kind of stress. – isherwood Jul 19 '16 at 21:07
  • Thanks for the link. I am familiar with the electrical soft start, not for mechanical wear, but for reducing peak load in renewable energy applications, such as a well pump. But I could see how in rush current in a brushed fan motor would reduce the life of the brushes. – donjuedo Jul 19 '16 at 21:13

I would only let the fan run constantly or on manual as you suggest if you have a variable speed fan in the unit that will change based on the call for heat/cool.

  • There you remind me. I guess my high efficiency unit had a variable speed fan while this one doesn't. My question, however, is does this do any harm? – Rob May 19 '16 at 22:33

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