Most people install their furnaces in out-of-the-way places, such as basements, attics, or utility closets. While these appliances aren't typically silent, they shouldn't make many noises loud enough to reach your living spaces. You may occasionally hear your furnace clicking on, but you generally shouldn't know your furnace is running aside from the sound of the air through your vents. 

If you can hear your furnace, you probably have an issue that requires attention. Surprisingly, you can learn a lot about what might be wrong based on when you hear the noise. This guide will provide a brief overview of what the timing of your furnace noises can tell you about the repairs you may need to make.

Noises Before Ignition

Natural gas furnaces will proceed through a pre-ignition sequence before they start. This sequence proves that the furnace's safety equipment is in good working order, ultimately preventing the furnace from igniting when there's a serious problem. This pre-ignition sequence includes engaging a small blower motor (the draft inducer) that pulls combustion byproducts through the exhaust flue.

If you stand close to your furnace, you will usually hear the draft inducer turning on before your furnace ignites or the main blower turns on. Any grinding, squeaking, or rattling noises before your furnace starts often originate with the draft inducer. These sounds may indicate a problem with the inducer and can be an early warning sign that your inducer motor will soon fail.

Noises During Ignition

Once the furnace runs through its safety checks and starts the draft inducer, the next step is to ignite the burners. A typical furnace burner assembly includes multiple individual burner units arranged in a row. The igniter lights the gas at the first burner, and special channels allow this flame to spread down the line.

One common (and frightening) noise you might hear during this stage is a loud bang resulting from delayed ignition. Delayed ignition typically occurs due to dirty or faulty burners, which allow excessive gas or combustion products to build up before igniting. Delayed ignition can damage your furnace, so you should take prompt action if you hear loud bangs during the ignition stage.

Noises While Running

If you can hear noises while your furnace is running, they likely originate from your ductwork or main house blower. Metal ductwork can sometimes rattle or pop as it heats and cools, and these sounds don't typically indicate a problem unless they're loud enough to be disturbing. On the other hand, sounds from your blower are more concerning.

A faulty furnace blower will produce similar noises to a faulty draft inducer. You may hear rattling or grinding, especially as the blower first turns on. As the problem progresses, these sounds may continue throughout the heating cycle. A weak or failing blower can cause your furnace to overheat, so you won't want to ignore these noises for long.

Contact a local heating repair service to learn more.