Noisy furnace fan

Old 10-12-12, 07:17 AM
Thread Starter
Join Date: Oct 2012
Location: Canada
Posts: 1
Upvotes: 0
Received 0 Upvotes on 0 Posts
Noisy furnace fan

Hello everyone. Maybe you can help.

My gas furnace fan makes a loud bang sound only when it shuts off, even if no heat is on, just the fan.

It has done this for the past 3 years and it's getting louder.

Any idea will be appreciated.
Old 10-12-12, 07:36 AM
SeattlePioneer's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Jul 2007
Location: Seattle, Wa
Posts: 4,469
Upvotes: 0
Received 1 Upvote on 1 Post
When the fan switches on, it pressurizes the duct system like a balloon, causing it to physically expand in size a bit.

When the motor shut off, the balloon deflates, and in some duct system you get a noise called "oil canning" as the sheet metal returns to it's normal size. Well designed duct systems reinforce the duct in various ways to avoid that noise.

Does that sound like what you are noticing?

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: