How to Decode the Sounds From a Furnace

There are several reasons why a furnace occasionally makes noises that grab attention.

There are several reasons why a furnace occasionally makes noises that grab attention. However, not all sounds are ominous signs. As it's difficult to tell the difference, here are some common sounds a furnace makes and what they could mean.

Normal furnace sounds

Here are some examples of relatively standard furnace noises:

• If the heating hasn't been used for a while, it will make a noise when it first comes on.

• Depending on how long the furnace has been installed, it may occasionally make a clicking or popping sound, which is more common in older furnaces.

• If the heater has several speed levels, it may make a noise similar to switching gears as it adjusts to the new speed setting. This sound can be dampened by insulating the heater.

• Chirping sounds are likely to originate from the mechanics (turning parts, etc.).

• A humming sound is typical as the heater ignites.

• Crackling sounds occur whenever the heater stops and are occasionally caused by the metal elements cooling down and contracting.

• Pinging sounds may arise from the metal connecting with the duct system.

Irregular furnace sounds

Here are examples of noises that shouldn't be ignored and will need to be addressed by an HVAC professional:

• A loud boom or bang could signal gas build-up in the heating system.

• The sound of metal clanking and scraping could mean a problem with the furnace blower wheel. In this instance, switch off the heater and contact an HVAC professional to examine the furnace.

• While screeching or squealing may make it seem like a serious problem, this isn't always the case. But a damaged or loose blower belt can cause the heater to make whistling or screeching sounds due to dry moving parts.

• Humming, rattling, or buzzing sounds aren't always a cause for concern and may arise from a loose screw or door. However, an HVAC technician can find the root cause and prevent more damage if that's not the case.

• If the furnace makes grinding sounds as it runs, this could point to the blower bearings being completely worn. This is usually the case for older furnaces. With newer models, it could mean that the belt tension has stressed the system.

• If flapping sounds occur whenever the furnace cycles, it could simply be an object stuck in the air intake. It could be something small enough to get through the vent but large enough to get stuck, like a piece of paper. Alternately, it could be something more severe. An HVAC technician can remedy this issue by inspecting the system and determining the cause.

Keep the furnace in pristine condition

Furnace systems make many noises. Some occur even though everything is ok, while others warn of the opposite. If concerned about some of the furnace's sounds, consider contacting a local HVAC technician. They will thoroughly investigate to determine the issue and advise on the solution.

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