Noises from Your Furnace: What’s Normal — And What’s Not

Noise curious

Posted: September 28, 2018

In our last blog, we explained a common noise you will hear (whistling) whenever you get a delivery for your basement oil tank.

Now, we would like to carry over that theme by discussing the various sounds you may hear from your warm-air furnace. As with any piece of equipment, many of the sounds you will hear are perfectly normal.

But the next time your furnace turns on and starts delivering heat, listen for the various sounds it makes and observe how long the sound generally continues. By doing this, you’ll be more aware of anything different, such as a noise you’ve never heard before.

To help you distinguish between minor and major problems, here’s a list of common sounds you may hear from your furnace. These are general guidelines provided solely for educational purposes. A correct diagnosis can only be made after a system inspection. (This is just one reason why we always promote the value of annual maintenance!)


This usually comes from the transformer; all transformers hum to some degree. If the humming begins to increase, it’s an early signal that the fan motor may be wearing out. Immediate attention is not required but an inspection should be done soon.


This often happens when the bearings in the blower motor wear out. If you hear this noise, shut off the system immediately to avoid further damage. Then call us for service.


If it’s an older system, the blower motor may need oil. There may also be a loose belt.


The blower wheel or motor may need to be rebalanced.


Unless it’s the whistling you hear from having your basement oil tank filled up, this noise could mean that a dirty filter is constricting air flow.


Abnormal air pressure makes ducts pop in and out. This can be caused by a clogged filter, an undersized or flimsy duct, or closed vents.


When air gets forced through your ductwork, you may hear creaking noises because the ducts are expanding and contracting. This usually doesn’t happen with a properly installed variable speed system. There will be reduced air turbulence because the system doesn’t “blast” on and off.

If you have any concerns about the operation of your heating system, please contact us and we’ll be glad to do a system inspection.