On Fri, 02 Feb 2007 19:23:20 GMT, Mike E. Fullerton
wrote:

On Fri, 02 Feb 2007 12:17:44 -0500, Goedjn wrote:

On Fri, 02 Feb 2007 10:55:59 GMT, Mike E. Fullerton
wrote:

We recently bought a 25 year old house. It uses gas heat. When it got
cold and the heat came on I noticed a very loud cracking sound when
the heat came on and again when it turned off. This is from the
expansion and contracting of the galvanized heating ducts in the
basement. The ducts are on metal hangers so they are not touching the
floor joists.

I have never encountered this problem in any other house I have lived
in. How to best fix this? Someone suggested putting a strip of plastic
vapor barrier between the hanger and the duct to allow slippage.
Couldn't that be a fire hazard?

If the ducts are hot enough to be a fire hazard, then
something is seriously wrong with your heating system.

Are these round or rectangular ducts?

Rectangular.

sometimes creasing the panels in those in
a big X will reduce the booming.