AC and fan question

Posted by Paul O. on July 17, 2005, 6:59 pm

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.

--
Paul O.
oplholik@gmail.com

Posted by Edwin Pawlowski on July 17, 2005, 7:05 pm

>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.

Look at the recent thread on Blower Motor. Yes, this is a god idea.

Posted by RP on July 17, 2005, 2:38 pm

Edwin Pawlowski wrote:

>>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.

>
>
> Look at the recent thread on Blower Motor. Yes, this is a god idea.

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

Posted by Edwin Pawlowski on July 17, 2005, 8:08 pm

> 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

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?

Posted by RP on July 17, 2005, 3:43 pm

Edwin Pawlowski wrote:

>>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

>
>
> Wow, just yesterday one of your esteem colleagues said exactly the opposite.

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.

>
> How does the fan reduce comfort level? By maintaining a more even
> temperature through out the house?

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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