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Old 10-04-2010, 09:57 AM   #1
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Oversized Furnace, Undersized Return Air vents and Low Heat Output.... ??


I just had a furnance "tune-up" done and the HVAC Tech reported the furnance was way oversized and the return grate too small. There are a total of (7) supply vents.

Anyways, for my sized home (1200 sq ft) he recommend a 60k btu furnace. Mine is a 125k btu.

He also mentioned a flow rate of 770cfms. This for the (7) supply vents. (110cfm/vent)

I also noticed a 10" pipe on the return air and the grate upstairs is 12"x 6". Both flow under 500cfm (??).

Would increasing the return air volume (larger return air grate) help with the heat output of our current furnace

Also, with the oversized furnace, would it be beneficial to add supply vents to the basement (no supply vents) Thereby make use of the extra furnace capacity ?

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Old 10-04-2010, 05:28 PM   #2
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Oversized Furnace, Undersized Return Air vents and Low Heat Output.... ??


Increasing the return would help. A little.

125,000? For 1200 sq ft. They must have though you wanted to heat the outside too.

While heating the basement will help you get more out of your furnace. it will also be a waste of money. Why heat the basement?

The right size furnace, could reduce your heating bill enough to pay for the new furnace in just a few years. Depending how warm you keep your house.

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Old 10-04-2010, 09:38 PM   #3
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Oversized Furnace, Undersized Return Air vents and Low Heat Output.... ??


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The right size furnace, could reduce your heating bill enough to pay for the new furnace in just a few years.
I know it. We're turning it into a rental in a couple years so it won't matter.

Will it be worth my while to increase the size of the return air intakes ???
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Old 10-04-2010, 09:47 PM   #4
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Oversized Furnace, Undersized Return Air vents and Low Heat Output.... ??


You are gonna get a lot of mad tenant calls. Put in a new furnace and you'll cure the problem. It's an investment not a loss..it's tax deductible too.
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Old 10-04-2010, 09:53 PM   #5
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Oversized Furnace, Undersized Return Air vents and Low Heat Output.... ??


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I know it. We're turning it into a rental in a couple years so it won't matter.

Will it be worth my while to increase the size of the return air intakes ???
No because the furnace is too large by two and half times.

You'd have to change the duct back if you do the furnace later.
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