Need help with furnace. Fast? I don't know..

I have bought a home recently. It was built new 2 years ago, and therefore I did not go through hiring someone for a formal home inspection. In any case, I don’t think home inspections cover appliances.

The heating furnace works fine, except that when the blower starts I hear this funny noise. The closest I can describe it is that it sounds like a long drawn whistle, that lasts for about 2 or 3 seconds and then goes away only to come back the next time the blower starts up again.

I am not too confident of going near furnaces and trying to inspect one at close range is not comfortable, especially when it is ‘live’.

What could be the source of this sound? Is it the belt(s) slipping, or something else? Is it just a way for the furnace to tell me that it is coming on? Should I be immediately concerned, or can I wait a few months for summer when the asking rates for the furnace repair guys are likely to be lower? Can I do something to find out the source of the problem and rectify it myself, or should I not even think about it?


It could be the belt on the blower slipping. The tension on the belt may need adjusted, or perhaps the belt is starting to go bad.

Whistling can also be a symptom of low gas pressure in the burner. You may need to have the burner adjusted.

ETA: You can check the tension on the belt yourself. The furnace should have a safety switch that keeps it turned off if you remove the cover. If you push down on the center of the belt it should feel fairly tight and you should only be able to push it maybe half an inch or so at the most. Tightening the belt is usually fairly simple if you are mechanically inclined. You just loosen the bracket holding the motor, push it so that there is enough tension on the belt, and tighten it back up.

Get closer to the furnace to see if the sound is coming from where the motor and blower are. It very well could be the belt slipping. Maybe it needs an adjustment or replacement. The reason it makes sense is that rubber is one of those things that shrinks when it gets warmed up as opposed to certain other things that expand. So after a belt slips briefly and warms up, it becomes tighter and can stop slipping and making noise.

If the house is 2 years old there will be no belt on the furnace. It will be a direct drive blower with no belt.

It is likely an acoustic air noise.

As the blower reaches full RPM/ full air flow is it likely sucking in-----or blowing out----air through a crack somewhere in the furnace or associated ductwork.

If you don’t want to call out an HVAC company, you can investigate it yourself. Start up the blower as many times as needed, and if you move/ lean on/giggle the door on the furnace, or around the ductwork you may find you can “alter” the sound. They may lead you to the source.

Also, you didn’t specify which blower. Theres a small blower (called an inducer) and a much larger main blower that distributes the air to your home. Which one is whistling? It many be that the screws that mount either blower needs to be tightened.

In any event, to answer your OP, it’s likely not dangerous. You can likely wait.

FTR…unless you live in San Diego or temperate climate, from roughly now through March 30th or so is the slowest time of the year. After that, in most places rates will definitely not be going down…

Air noise can be annoying but many times they can be found through investigation. A common source is air whistling around a filter. Take the filter out for a moment. Does the noise go away?

Monkey with this a bit. you may just find it and save the cost of a service call.


I’m not sure exactly when residential furnaces stopped being made with belt driven blowers, but I would guess this to be the late 60’s. Certainly by the mid 70’s they were largely----it not all----direct drive.

Nowadays, you can’t find a residential belt driven furnace. I see hundreds of furnaces every year and I can count on one hand the amount of belt driven furnaces I see.