heat run bangs

Old 10-15-10, 06:42 AM
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heat run bangs

In March I had a new furnace put in to replace an Armstrong unit that served me well for 25 years and never had this "bang issue" When the furnace first comes on in the morning is when it is most noticeable, shortly after it shuts down I hear this bang and actually located an area of the square run where it is coming from. That along with some "whistling" that is coming via the return air, it drives me nuts. Since neither was an issue, anyone give me some possibilities that should be looked at or might be the cause and possible a solution.
Old 10-15-10, 07:10 AM
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It could be that the new furnace has a bigger/stronger blower, your ductwork may be undersized.

How many BTU was the old furnace, and what is the new one?
Old 10-15-10, 09:21 AM
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Yes, a larger BTU input furnace can cause such a problem. Also, the fan motor speed may be set too high.

That really needs to be checked by the contractor who installed the furnace, since turning down the fan speed could cause the furnace to overheat.

The contractor who installed the furnace should check out your complaints. Usually the contractor guarantees their installation for a year.
Old 10-16-10, 10:54 AM
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Undersized ductwork is the most common cause with unbraced or too thin a sheet metal used being the second most likely. Undersized ductwork in residential systems seems to be the norm rather than the exception.
Old 10-16-10, 02:17 PM
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I agree with furd! Duct under sized

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