Q. My furnace emits a loud bang when the burner comes on. What is causing this and how can I prevent this from happening? We do plan to have it serviced for the winter but aside from the bang it seems to be running fine.
A. The bang sometimes referred to as “oil canning” is normally explained as heat duct noise. When the furnace burner ignites, the hot air rises into the hot air plenum which is the large metal duct on top of the furnace. When this duct gets hot it expands and pops out, when it cools down it pops back causing that aggravating banging noise. You can correct this by wrapping two strips of perforated metal strapping around the duct and tighten like a belt with stove bolts.