The Call

I got a call from a perspective customer last week saying her furnace was just too loud! She wanted to know what to do to stop the furnace making noise. This problem may appear to be a bit vague in nature. But as I reflected on it, seems like I’ve gotten a number of calls like this in the past. In some cases, I’ve found that folks really do know if there is a problem with something in or around their home simply by listening.

Although this may sound “funny”, it actually rings true! Just like with your car; if it sounds different from what you are used to, then there just might be something wrong. How many of you have been in the following situation? You take your car into a mechanic and they try to have the car make the same  suspicious sound back.  But he car, of course, never makes that same noise that it did for you! Normally the mechanic would check it out. Perhaps he finds nothing is actually wrong with your car. Then you at least have some kind of relief knowing it was looked at by a professional.

Tracking Down the Problem

Off I went to the homeowner’s house to take a look see at a “noisy furnace”. In most cases, furnace making noise may indicate a mechanical problem, airflow reductions or a clogged burner, etc. Loud noises coming from your furnace, especially while it is running, could be caused by any number of issues.

Possible Causes for Your Furnace Making Noise

A loud noise from the blower or motor:

This may indicate that you have a problem with the fan/blower that moves hot air through your ducting/vents. That might be due to the fan bearings being worn out. In which case, these bearings would need to be replaced. If the noise is coming from the furnace’s motor, it may be due to a phenomenon called “bouncing.” You may be able to alleviate this bouncing by placing a sturdy piece of Styrofoam under the motor’s squirrel cage (stationary covering around the motor). However, the motor bearings are most likely worn out, and again you will have to have them replaced.

A whistling noise:

If your furnace is whistling, one possible cause could be a clogged filter. This is especially true if the whistling noise has just started recently. A clogged filter can cause the fan to suck air from anywhere it can. Tiny holes or spaces in the ducting can generate a whistle if any significant air is being sucked through them. To test out this possibility, pull the filter out and replace it with a new filter to see if the whistling stops. This is better for not only reducing the noise, but also to reduce the wear and tear on your fan motor.

A rattling noise (vibration):

If there’s rattling noise in your furnace and/or ducting, such vibrations may have simple fixes. Here are a few things you can do to try to stop the rattling:

  • Add additional screws to any loose ducts
  • Apply duct tape to any loose ducts or other pieces of the equipment
  • Add rubber or cork pads under the furnace. (You can most likely raise the unit with a pry bar, just enough to slip something thin underneath.)

A banging noise (when the furnace turns on):

If you hear “banging” when your furnace turns on, there are two likely reasons. One is that your duct work could be “oil-canning,” or flexing when the pressure changes. Or, it could be due to a very small “explosion” called “ignition roll-out.”

Oil-Canning Ductwork:

If the issue is oil-canning ductwork, you may be able to fix this yourself. You should listen carefully to the furnace to see if the banging is coming from somewhere in the ductwork. If oil-canning is the problem, there is probably a weak spot in one of the ducts that needs additional support. You may be able to fix this by screwing a slightly thicker piece of metal across and onto the weak spot. Of course, this is relatively easy if the particular section of ductwork involved is exposed and near the furnace. If it’s behind a wall however, it certainly will be more difficult to do the above. But chances are, if you’re okay with the initial noise/bang, you really don’t have to change anything.

Ignition Roll-Out:

The other possible cause, is called ignition roll-out. It is not very common, but it can be alarming. It’s a little explosion when the furnace starts up, or a burst of flame bigger than it needs to be. To see if the banging is caused by a gas-ignition problem, watch the furnace start up. If you can see into the furnace through the doors, you should be able to see what’s happening. If not, listen in order to pinpoint from where the noise is originating. Watch to see if the doors on the furnace are at all shaking. If they are, then try this again with the door to the burner compartment open, to see if the banging still occurs and if you can see what happens when it does.

If you see a somewhat larger flame or shaking associated with your noise, you may have identified a potentially dangerous problem. You should call in an HVAC specialist to correct it. Trying to deal with the gas portion of your furnace should be left to professionals, unless you are really mechanically inclined. On the positive side, newer furnaces have a “roll-out sensor” that will shut the unit down if this problem occurs.

A loud noise (in general):

Similarly, if your oiled fired furnace is making a loud noise just as it starts, this could be caused by a problem referred to as “delayed ignition.” This may occur when unburned oil builds up in the fire box chamber and is ignited all at once. This can be a dangerous situation also, and you should have an HVAC professional take a look at it as soon as possible.

In Summary

Listed above are just a few of the potential noise problems that you may face in dealing with your furnace. Attempting to fix simple mechanical problems may be to your advantage in cost savings, but if you have any serious concerns about the origin of the noise, please give us a call to be on the safe side. You can click here or call us at 1-412-461-2198. Let us help you with that loud racket! We’re always glad to help out and/or make recommendations!

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