Knocking noise coming from furnace...

[brian374]

I have a furnance located in my attic to control the upstairs of my home. Only when the heat is on, I hear a loud knocking noise coming from the unit. It does not make this noise while running, but can be heard after it shuts off - it may be immediate or several minutes. Sounds like something is turning and rubbing against some metal. Very loud. It does not make this noise when the AC is on. Any thoughts? While sitting in my attic, I narrowed the noise to come from the unit itself. I orignally thought it was the line coming from the heat pump outside vibrating on wood, but that's not the case. Thanks.

[m kilgore]

When was the last time the unit was serviced? Sounds like that is what you should do as we can't hear it from the net.

[the dangling wrangler]

Time for a service call.

[brian374]

The unit is 1 year old. Brand new house. Just wondering if anyone has had a similar issue and can pinpoint the cause since it only happens when the heat is selected and does not occur while running. Exhaust? I've had 2 techs out over the last year, but of course, they never can hear it. But I have the builder coming back this Thursday to troubleshoot.

[the dangling wrangler]

The unit is 1 year old. Brand new house. Just wondering if anyone has had a similar issue and can pinpoint the cause since it only happens when the heat is selected and does not occur while running. Exhaust? I've had 2 techs out over the last year, but of course, they never can hear it. But I have the builder coming back this Thursday to troubleshoot.

It should be a warranty issue, if it's only a year old. I don't think the builder can help out a lot here. If it's a gas furnace, it could be the heat exchanger expanding and contracting. That's about all I can say in the public forums.

[Mr Bill]

You said it did not make the noise in the a/c mode, most gas furnaces run the a/c and the heat on different speeds, maybe it's doing it in the heat mode because the blower is running at a lower speed, but a service company could probably fix it fairly quick.

[brian374]

It's all electric. The noise occurs when the blower is off and no airflow is felt from vents. Just wondering if there is some kind of exhaust that runs in heat mode after it shuts off.

[coolwhip]

Its the installation manual banging around in the blower section.

[mr horsepower]

It's all electric. The noise occurs when the blower is off and no airflow is felt from vents. Just wondering if there is some kind of exhaust that runs in heat mode after it shuts off.

this is not a d.i.y. site which is why you are not getting very detailed answers.

you are having the builder come out to look at it, which is fine, but i'm not sure he is the best one to remedy the situation. i would have the installing contractor come out to inspect it.

in answer to your question - electric strip heaters do not require any type of flue piping, vent piping or otherwise.

good luck on the repair. i would hope if it is within a one year period of the install that the cost would be nothing or close to it.

[the dangling wrangler]

Its the installation manual banging around in the blower section.

I've seen that before too. Or they used to put a folded piece of cardboard, inside the blower wheel. Again, it's kinda hard to diagnose over the 'net.

[aselez]

what is brand name and model #