Furnace InstallationWhy Is My Heater Making That Loud Noise?


Furnaces are big metal contraptions with internal moving parts, so it’s not surprising to hear a few noises now and then when the heater turns on or off. Your heater may be trying to get your attention with unfamiliar noises.

Forced air furnaces are highly efficient heating systems that can quickly and evenly warm-up a house, but they also double as a central air conditioner in the summer. Due to the dual jobs they perform though, the many composite parts that make up these systems can cause noises throughout the house as heat travels up through the registers.

The majority of noises a heater makes aren’t cause for alarm, but just to make sure, here are some of the sounds you may hear from your heater and why:

#1 – Screeching

If you hear a screeching noise coming from your furnace, it’s most likely a result of problems with a belt, bearing or the motor. While this isn’t hazardous, if left in poor condition, it can cause larger repairs later.

#2 – Chirping

A chirping sound from your furnace mostly occurs when the unit has not been in use for a while and could just be an indication that the heat is coming on. After the furnace has warmed up and run for a few minutes, the noise may stop. If the noise continues or grows worse over time, it may need a belt replacement. In this case, it’s probably a good idea to contact a furnace repair technician to check the unit and make any necessary repairs.

#3 – Rattling

A rattling sound coming from the furnace could mean there is a panel loose and can be fixed by simply tightening the cover panels. If you have checked the panels to make sure everything is tightened, the rattling noise may be from your furnace expanding and contracting the metal parts as they change temperature. However, if the rattling noises still continue it may be something more serious and a furnace repair technician should be contacted.

#4 – Clanging

If a clanging noise occurs only when your furnace first starts or right after it stops blowing hot air, the sound probably is caused by expansion and contraction. The metal housing, vents, pipes, and other parts make clanging and banging noises as they heat up and cool down. This is normal and shouldn’t indicate a problem.

#5 – Knocking

A continuous knocking sound though that occurs while the furnace is running is a signal that a furnace repair technician should be contacted. The two most likely sources of the continuous sound are a damaged or cracked belt, or bad bearings.

#6 – “Boom” or “Bang”

A loud boom or bang coming from your furnace could be one of two things. If the boom or banging noise is located at the heater, a delayed gas ignition is most likely the problem. Delayed gas ignition is when gas in the furnace builds up rather than igniting immediately. When the gas finally ignites after a while, a mini-explosion happens and can harm your furnace.

The second cause of a loud boom or bang could be the metal ductwork that’s expanding and contracting when the heating system’s blower starts. Try changing the air filter and make sure your home’s supply vents are open. If that does not solve the problem, you’ll need to contact a professional to find a solution.

#7 – Humming

If a humming sound is coming from the furnace, begin by trying to pinpoint where the hum is originating from. One of the most common problems is that the blower motor makes a humming sound. If this is the case, then the first thing you should do is turn off your motor and allow it to cool. When it has cooled down to a safe temperature, check the motor, the humming could be the result of something as simple as improper lubrication.

Once your house is warm, the furnace blower begins to naturally run on a slower speed. But if your blower motor slows down unusually and makes a humming sound when it has slowed down, it might be due to a fault in the capacitor and the motor and may have to be replaced. This problem is typically caused by dust and dirt in your filter which can block filters and make the motor work harder to push out air.


HVAC (heating, ventilation, and air conditioning) systems require the expertise of a professional for proper installation, maintenance, and repairs. If you are having problems with your furnace, it is important to remember to always contact a heating and air conditioning specialist. By taking care of and properly maintaining your home’s HVAC unit, you’ll have an efficient heating and cooling system that will provide for your family’s comfort for many years to come.

Have questions about a strange or loud noise coming from your heating system? Contact MM Comfort throughout the Seattle area to help with your Heating and Cooling needs. Call us at 425-533-9058, or use our online contact form to arrange for a free heating and cooling consultation.


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