Dear Expert:

I have a new Carrier 2-stage 80% efficiency furnace in my home. Lately I heard big bang noise every time about 20 seconds after the furnace shuts off. It sounds scary to me since I don't know what's wrong? :eek:

Does anyone have hint about what it is and how to solve it? Will that harm the whole heating system?

Thank you!

Could be the metal duct popping (oil can pop). If it is new call back the contractor that installed it for you. They might need to cross break a piece of the duct to stop the noise.

Hi, hvac1000:

I called the contractor. But he said it may be due to I block several of the registers or the filter is dirty. I checked the filter and feel it is not too bad. Do you think it is true that the banging noise is due to the blockage of the registers?

Thank you for your help!

It could be possible. Did you open the registers? Did the bang stop?

I did try to open all the registers and the bang noise is very occasional but not none. However, I found that if the furnace is fired on to increase the temperature for 1 degree, then no matter I close some register or not, there is not bang noise. However, if the furnace needs to work to increase 2 or more degrees then the opening of the register did matter. Any clue?

Thank you!

It is the duct more than likely. You can try to watch the furnace to see if the gas valve has a delayed ignition on the second stage but I seriously doubt that.

Ok. I will try to watch the furnace. Hopefully it is nothing wrong with my new furnace.

However, if it is really due to the duct, will it hurt the whole heating system or the house? Is there way to solve it?

Thanks!

The fix is to call the contractor back that did the new install for you. It is there responsibility.