Four Strange Heating System Noises And What They Mean

When your furnace is operating properly, it should make very little noise. There will be a clicking sound when it switches on and another clicking sound when it switches off, and of course the blowing noise as air moves through the ducts. Any other clinging, clanging, banging, or rattling is abnormal and indicates that your heating system has a problem that likely needs repairing. To assist in diagnosing such issues, here's a look at four strange heating system noises, what they mean, and what you should do about them.

Banging that seems to come from within the ducts.

Do your ducts make a banging, crashing, metallic noise whenever the heat first turns on? You may notice that this is most pronounced on the coldest days or after the heat has been off for a while. This noise is generally caused by portions of the duct expanding in response to the change in temperature as the warm air blows through them. It's not a major issue, but since the banging can be loud and distracting (especially in the night), most homeowners want it fixed. Your HVAC technician should be able to amend the issue by replacing the offending pieces of ductwork with metals that experience less expansion and contraction. Placing a layer of insulation around the ducts may also help, as this will keep the metal from cooling down so much between heating cycles.

Rattling noises.

If you hear a rattling noise whenever the furnace is on, check your furnace's cover panels. Rattling can sometimes be a sign that these panels are not placed on tightly. Typically, this is a problem you can address yourself. Every furnace cover attaches a bit differently. Some screw on -- and to tighten them, you'll just need to tighten the screws. Others "clamp" on with little pieces of metal. To tighten this kind of cover, you can use pliers to bend the metal flap more tightly around the edge of the furnace.

If adjusting the cover does not stop the rattling noise, then contact your HVAC technician. There's a chance the rattling is caused by a bolt or part inside the blower unit having worked its way loose.

Buzzing or humming noises.

Does your furnace emit a sound similar to that of buzzing bees when it's running? Or maybe the noise is more like a low-pitched hum. These types of noises are tough to diagnose. There are a couple of common causes you can try addressing yourself before calling in the pros:

  • Replace your furnace filter. Dirty filters can let debris settle inside the unit, making certain parts "heavier" and causing buzzing noises as they vibrate.
  • Make sure nothing is leaning against the furnace. It sounds silly, but if there's something leaning against the furnace, it may vibrate against it, causing a buzzing noise as the furnace runs.

Other possible causes of a buzzing or humming noise include a lack of lubrication in the motor, a failing capacitor, and a poorly adjusted pilot light. Unless you have experience working with furnaces, these are all issues that are best left to a professional. However, they are all rather minor ones that should be able to be repaired quickly and inexpensively. Unless your repair technician tells you otherwise, you should be able to keep using your furnace in the meantime.

Squealing noises.

If you hear squealing or whining noises, turn off your furnace until the repair technician arrives. This sound could indicate a broken blower motor, which could overheat and present a fire risk of you continue to run it. The sound may also simply indicate that your blower belt needs adjustment or replacing, which is a more minor issue. However, since it's tough to tell the difference based just on sound, you're best off not using the furnace until repairs are made.

If your furnace is making strange noises, don't just ignore them. Use the guide above to get to the bottom of the issue so you can enjoy quiet, safe heating once again. Contact a company like Winters Heating Cooling & Indoor Air Quality for more info.