On 30 Dec 2004 04:33:18 GMT, (AUSTIN1880) wrote:

there is a banging noise in heating duct shortly after furnace comes on it
only happens once. Is this due to the expansion of the sheet metal?


Yes, it's called the "oil can" effect. Just a nuisance, nothing more...

Ed

Actually, its called, "The ductwork probably isnt sized properly".
Most likely, the furnace is too big or the ductwork is too small.
Either way, it means a shorter life span for your heat exchanger and
associated temperature controls in your furnace like the high limit.
Then of course we can get into the air conditioning but thats a whole
nother story.
Bubba