Air Handler making noises ?

[bigdog]

My HVAC Air Handler making noises ? Heat comes on, and starts blowing warm air through ductwork, but when furnace shuts down, the Air Handler makes a loud 'clunk' the shuts off. Furnace to the best of my knowledge is acting as it should.

System is a gas (natural gas) fired furnace, and mounted in the garage. The Air Handler is located, in the attic above a bedroom closet

I'm saying the sound is coming from the Air Handler, because I can hear it shut off in the bedroom closet ceiling, I'm not what else it could be ?

Thanks for your feedback, much appreciated !

[WinnisquamZ]

Curious. Did you recently replace the air filter? If it’s dirty or in my case used a dense new filter where the system recognizes a weak air flow it will shut down


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[bigdog]

Originally Posted by WinnisquamZ

Curious. Did you recently replace the air filter? If it’s dirty or in my case used a dense new filter where the system recognizes a weak air flow it will shut down


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House is new to me, and about 15 yr old. Will check filter ASAP, as this should be replaced a few times each year, and are cheap.

Thanks for the tip !

[CTYankee]

If a change of filter doesn't do the trick it could be an air duct flexing. It's a common source of noise that occurs when the pressure inside the duct lessons when the system shuts off.

[8gv]

Originally Posted by CTYankee

If a change of filter doesn't do the trick it could be an air duct flexing. It's a common source of noise that occurs when the pressure inside the duct lessons when the system shuts off.

This is likely to be the answer.

[dpg]

Or... Bearings in your fan motor going? Sgouldn't cause a "clunk" but they do get noisy when they wear.

[bobkatfly]

Originally Posted by CTYankee

If a change of filter doesn't do the trick it could be an air duct flexing. It's a common source of noise that occurs when the pressure inside the duct lessons when the system shuts off.

Yes, this is usually what causes this noise. I had a house in Nashua with a forced air system that did this. The thin wall duct systems that don't have adequate bracing do it all the time. They expand (belly out) when under pressure and temperature and suddenly contract (belly in) when the fan stops. It can be worse if the ducts are insulated because the metal gets hotter.
Has this just started or has it be doing it all along?

[bobkatfly]

One other thing. Check if there's a damper in the duct system. I think some systems used them to prevent back flow from the air conditioning circuit entering the furnace. When the furnace runs, the damper opens then closes (with a bang) when the fan stops. Essentially a check valve.

[bigdog]

Originally Posted by bobkatfly

Yes, this is usually what causes this noise. I had a house in Nashua with a forced air system that did this. The thin wall duct systems that don't have adequate bracing do it all the time. They expand (belly out) when under pressure and temperature and suddenly contract (belly in) when the fan stops. It can be worse if the ducts are insulated because the metal gets hotter.
Has this just started or has it be doing it all along?

Forgot to preface this conversation, by saying I now live in S.C. near Hilton Head Island...

This noise has just started, however, this has only begun since I just started using the 'Heat' for the season, up to know I've only been using A/C.
The heat only kicks on during the night, when temps drop below 50 degrees.
After about 9am, the heat does not come on.

When the A/C/ was on, I never heard this noise.
Thoughts ?

[bigdog]

Originally Posted by bobkatfly

Yes, this is usually what causes this noise. I had a house in Nashua with a forced air system that did this. The thin wall duct systems that don't have adequate bracing do it all the time. They expand (belly out) when under pressure and temperature and suddenly contract (belly in) when the fan stops. It can be worse if the ducts are insulated because the metal gets hotter.
Has this just started or has it be doing it all along?

Forgot to preface this conversation, by saying I now live in S.C. near Hilton Head Island...

This noise has just started, however, this has only begun since I just started using the 'Heat' for the season, up to know I've only been using A/C.
The heat only kicks on during the night, when temps drop below 50 degrees.
After about 9am, the heat does not come on.

When the A/C/ was on, I never heard this noise.
Going to crawl into the attic today, thats where furnace is located, to check air filter, then report back.

[bobkatfly]

You said the air handler is in the attic, right? When you're there, look to see if there's a damper before or after the fan and try to observe it when the system shuts down. You might be able to see the end of the damper shaft coming through the duct. Very possible it's the source of noise. If you have separate zone ducts instead, there may be dampers there to balance the system through I wouldn't expect these to be noisy as they might be motor controlled.
If the noise only happens when the furnace shuts down normally, I don't think it would have anything to do with the filter.
Good luck

[TheProfessor]

The squirrils and/or chipmonks and/or mice . . . are just shutting their door.

No big deal.