AC and fan question

I am wondering if it is much cheaper to run the furnace fan continously as the air coming out of the vent is cool enough for part of the day rather than the AC coming on and going off all day. Thanks.
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Paul O.
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Look at the recent thread on Blower Motor. Yes, this is a god idea.
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Edwin Pawlowski wrote:

It's much cheaper to leave them both off.
If you're ok with just the blower running then odds are you'd be ok without it running as well. A ceiling fan is much more economical and vastly more sensible. In many (if not most) cases, running the blower continuously will reduce the indoor comfort level. It not only acts to introduce heat into the conditioned space but moisture as well. You may get a spurt of minor relief by the low velocity air movement, but in short order it'll have defeated its purpose.
hvacrmedic
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Wow, just yesterday one of your esteem colleagues said exactly the opposite.
How does the fan reduce comfort level? By maintaining a more even temperature through out the house? Where is it introducing heat from?
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Edwin Pawlowski wrote:

That would be Harry. Harry was wrong yesterday. He then came back and made a valid point, but it didn't jive with what he originally said. Moving air will generally cool a wet surface, e.g. a perspiring person, which though in general is true at a modest temperature and RH, this is not the same as saying that moving air will keep the house cool, which it will simply not do unless there is some strange situation in place such as flow through a cold basement.

An even temperature means that the hotter areas are cooled at the expense of heating the cooler areas. If you have a particular section of the house exposed to direct sunlight and/or poorly insulated, and if you're going to be staying in that section, then you might get by on modest days by running the blower only. More often than not the entire house will increase in temp and RH when running the blower. There is no rule of thumb here, but it is definitely wrong to make a blanket statement that it's a "good thing to do".
Where is it introducing heat from?
The electrical power input to the blower motor is all converted to heat. Any condensate lying in the pan will revaporize, and then there are possible duct leaks that will cause infiltration of outdoor air. In addition, if the ductwork runs overhead you'll pick up attic heat. There are many many more possible sources of heat and moisture infiltration associated with running the blower.
hvacrmedic
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Not true! About 80% of the electrical power going to the motor is converted to moving the air through the duct. The remaining 20%, the motor loss of efficiency goes out as heat. My percentages are a guesstimate, it depends on the efficiency of the motor, but 80/20 is pretty close. If ALL the electrical power goes to heat you have a big problem! Greg
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Greg O wrote:

But that moving air will slow down releasing the energy back to heat as it slows down.
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Joseph Meehan

Dia duit
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Joseph Meehan wrote:

Close enough.
hvacrmedic
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Steve from CBHVAC also sait he runs his blower all the time.

In parts of the country with basments, this is not a strange situation at all.

Same as with a blanket statement this is is a bad thing to do.

True, but it is not a major factor. How do you allow for it doing the heat load calculations?

If the system is designed and properly maintained, it will not have a lot of condensate in the pan, ducts will not leak, and ducts in the attic will be insulated. Leaking ducts inside the house will not cause infiltration as they are merely circulating what is already in the house.
Running the blower may not be the best in every case, but I see it as a benefit in more cases than not.
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Edwin Pawlowski wrote:

True, but it is not a major factor. How do you allow for it doing the heat load calculations? Ed, the blower motor heat is already subtracted from the gross cooling capacity by the equipment manufacturer. Typically 1500 to 3000 BTUs per hour.
The moving air will feel like a breeze in mild weather, even out temperatures through the house and raise the humidity some, typically 10 to 15% RH. Most of the moisture is re-evaporated from the coil, only a little from the drain pan. My tests with a data logger indicate 10 to 15% in average weather conditions. In extreme heat, the compressor won't shut off, so there will not be re-evaporation, except at night.
In the OPs case though, since he has no AC, that will not be a problem.
The electric use will be 1/2 to 1 KWH per hour. With my electric rates and my blower, that would add about $25.00 each full month if I ran it 24/7 and did not have any AC at all, If I had AC running 50% average duty cycle, that would only add about$12.50 per month.
Stretch
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as
a god idea? maybe a good idea...
Just kiddin around wit ya....
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On Sun, 17 Jul 2005 17:51:26 -0400, "HeatMan"

sly devil!
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--
-john
wide-open at throttle dot info
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