Leaving fan on with a/c or not?

[Needingadvice]

Hello, I was wondering what peoples preferences were regarding leaving furnace fan on or off when using the a/c. Does it make the system come on less this way? Right now my ac seems to come on 3 times an hour for about 10 mins at a time.

[HVAC/Stud]

My 2 cents

What are you trying to gain?
What size is your A/C?
What brand and model is your tstat?
Do you have a EAC?

Running your blower will not remove heat. It will add heat(blower motor).

If you have a standard system, dont't waste the energy.

STUD

[mark beiser]

It depends on a lot of factors, but if you live in an area where humidity is an issue, have a standard blower motor, or have ducts running through the attic, leave the fan on auto.

[Needingadvice]

I have a high efficiency furnace with vs blower. Not very humid where I am, more dry heat here in Alberta.

[jmac00]

with the Variable speed blower, by leaving it in the "on" position, it will help even out the heat & a/c throughout the home. If you have a High efficiency air cleaner it will help clean the air.

Basically by leaving the fan *on* you will be more comfortable.

Now, a VS blower will not "fix" poor duct design, but with a constant air flow, those rooms the get less air or are cooler or warmer, will tend to be more comfortable with constant air movement

[beenthere]

The 3 times an hour is because of the CPH setting of your thermostat. Blowerbeing on or off has no bearing on it.

[Needingadvice]

Would you think that is a good setting beenthere? I was at the mercy of the installer when they came. I have the Lennox Comfortsense 5000 as a thermostat.

[Needingadvice]

Also thanks to the others on this thread that shed some light on things for me.

[beenthere]

A 3 CPH is the average setting. And works well for most systems.

[tipsrfine]

Leaving the fan on can increase infiltration/exfiltration, which counteracts any efficiency from your high efficiency unit.

[motoguy128]

Leaving the fan on can increase infiltration/exfiltration, which counteracts any efficiency from your high efficiency unit.


Depends on wher the ductwork is located and how it's run. In the north, it's usually inside hte conditioned space, or at least in semi-conditoned spaces.

I don't see much harm at leaving running year round if you like the more even temps and constant air movement. WIth a VS blwoer, the continous fan speed is usually only 50% and consumes around only 50-90Watts. I run both of my system on "circulate" so they run abotu 1/3 of the time.

[tipsrfine]

Depends on wher the ductwork is located and how it's run. In the north, it's usually inside hte conditioned space, or at least in semi-conditoned spaces.

I don't see much harm at leaving running year round if you like the more even temps and constant air movement. WIth a VS blwoer, the continous fan speed is usually only 50% and consumes around only 50-90Watts. I run both of my system on "circulate" so they run abotu 1/3 of the time.

Even ducts inside the envelope can cause pressure imbalances throughout the home. Lots of homes use wall cavities as returns, and that adds to the problem.

[Mr Bill]

Leaving the fan on can increase infiltration/exfiltration, which counteracts any efficiency from your high efficiency unit.

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[tipsrfine]

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I agree on many things you say, I just don't always say so.