When our heat turns off, we hear a loud bang, (we have gas forced hot air heat), any ideas what this is?

Question

This has never happened beofre and we've lived in the house for 8 years. Should I be concerned and what can be done to prevent it?

A guy was out last week and changed the filter. We didn't have this noise until he was here.

Answer 1

I would imagine he may have installed a filter that is pleated and catches more dirt and allergens? (Especially if you asked for this?) This might behave the same way as a clogged filter... The blower creates a vacuum pulling against a higher grade filter sucking in the sides of the air box. When the heat goes off the sheet metal pops back into place.

Or perhaps it is a simple as one of the panels was not put properly back into place from the service call?

If it is because of a better filter, you can have some small angle iron riveted to the box to reinforce it, preventing the banging.

Answer 2

I'm not sure if the filter guy could have done anything to your unit, but you should probably get a gas certified plumber to check things out. It may be that your main burner valve is slow to shut off the gas flow when the t-stat is satisfied. The resulting extra bit of gas that escapes is then ignited by the standing pilot and in a very minor way " explodes ". Hence the bang. I have also dealt with similar problems involving furnace heat exchangers with cracks in them. Gas is great, but nothing to fool with. Call a pro.

Answer 3

It's the pipes contracting. When the hot air is in the pipes, they expand slightly due to the heat. When it is shut off, the metal contracts because it's colder. I used to live in NYC, and our heat pipes made these awful banging noises all the time.

Answer 4

You could try cleaning or replacing the air filters.

Answer 5

could be the pipes contracting