A lot of furnace blower motors are going to produce a quiet hum while operating which shouldn’t bother you at all.
However, a loud bang, rattling, squealing, and slapping sounds can be an indication that there is something wrong with the blower. The root cause can be loose motor mounts, an object caught in the blades, and a weak belt.
Related: Furnace Noise Problems
Why Does My Furnace Make a Loud Noise When It Starts?
There are quite a few noises that you can hear coming from the furnace when it starts the heating cycle. Some of them are normal (like a click when the unit fires up and a non-disruptive dull hum).
However, there are some loud sounds that can indicate that there is a problem in the system.
There is an issue with the ignition system
One of the first things that happen in a furnace when you turn it on is the creation of combustion.
You will hear a single click if the igniter doesn’t have trouble lighting, but if the element is struggling, then you’ll be hearing a clicking noise for quite some time.
The igniter won’t be able to light, if the burners are dirty, gas is not reaching the system, the flame sensor is faulty, or if the pilot light/thermocouple is extinguished or broken.
There is a delayed gas ignition issue
If you hear a loud bang when you start the furnace, then it might be because the unit is not igniting right away.
In case the ignition is delayed, the gas will have a few seconds to build up in the chamber. When the furnace finally lights, this gas is going to cause a small explosion that creates a banging noise.
Dirty burners, a broken pilot light, too much air mixed with gas, or a low gas supply can be to blame.
The ducts are contracting and expanding
If you hear a bang a minute or two after you have turned the furnace on, then it might be because the ducts are contracting and expanding. While the furnace is operating, it creates different pressures which can cause the ducts to pop.
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Related: How Hot Can Ductwork Get?
This sound is normal, but if it gets too loud, then it looks like you have a dirty air filter, obstructed or closed vents, or the ductwork is too small for your furnace.
What Does a Bad Blower Motor Sound Like?
A blower motor is an essential part of your HVAC system as it is responsible for pumping the air through the system.
Unfortunately, this component is subject to the most wear and tear which, in its turn, can cause quite a few problems.
A banging and rattling noise
Yes, a banging sound can be coming from delayed gas ignition or popping ducts, but the blower motor can also be making a loud bang. Especially, if there is an issue with the assembly or the actual blower.
If you hear a rattling sound, then the chances are high that the motor mounts (or any other hardware) have become loose. At this point, the blower might be out of alignment or a part had disconnected from it, so calling a professional is a must.
A slapping sound
It looks like there is something caught in the blower blades.
Such a noise doesn’t necessarily indicate a dangerous situation, but do bear in mind that if there is debris or an object that constantly produces resistance, the blower motor is going to wear down a lot faster.
If there is a motor bearing issue or the belt is weak, the motor can start to squeal.
Thankfully, belts are relatively cheap to replace. You can also try adding some lubricant to make the blower motor quieter.
If you hear any of these furnace blower motor noise when starting, the best decision is to turn the unit off, let it cool down, and then examine the blower motor (you can call an HVAC expert to do that).
Why Is the Blower Motor Making Noise?
New furnaces are very quiet and even though some parts of the system will naturally make some noise, these sounds should not be causing any inconveniences.
Most of the units produce a low humming noise while they are working. Mainly, because of their moving part – the blower fan that is attached to the motor.
So, it is normal for a mechanical unit to produce some sounds, but if, throughout the time, the noise has become louder, then you should definitely check the system as there might be something wrong.
How Do I Lubricate My Furnace Blower Motor?
There are two types of blower motor ‘systems’.
The direct drive model has a motor that is attached directly to the fan. In a lot of cases, such motors have sealed bearings which means that they don’t need to be lubricated.
The ‘traditional’ belt drive fan motor has a belt and oil ports that need to be lubricated once a year.
Usually, the blower fan motor is located on rails, at the bottom of the furnace. It may also be behind an access panel that you would have to unscrew.
- Once you have found the blower motor, inspect the components to locate the oil ports. They are the parts that are sticking upward, located on the side of the motor.
- There is an oil port on both sides. At times, they can be covered with a colorful cap.
- If the port has a cap, remove it and put a few drops of special oil into the ports. Be careful not to overfill the little thing as this may result in a leak and hard-to-clean stains.
- Put the caps back and replace the access panel, if necessary. Come back next year.
Usually, you would have to apply not more than 2-3 drops of the oil.
Tip: do not use all-purpose oil. Go for a special bearing oil or a 10-weight nondetergent motor oil.
While you’re lubing the motor, you should also check the belts. If the part looks worn out, then you would have to replace it.
How Do I Make My Furnace Blower Quieter?
A furnace blower is the only moving part in the system and, of course, it will be making some noise. But if you want your furnace to be as quiet as it can possibly be, then take these few tips into consideration:
- Lubricate the motor regularly to get rid of the squealing sounds
- Tighten the belt if it’s loose or remove the part if it has worn out, to, once again, avoid squealing noises
- Check the fan for bent blades, dirt build-up, and worn bearings – all these things will make the furnace’s humming more intense. Replace any loose parts.
- Add more ducts. The blower might have insufficient return air if it is whistling.
- Replace the rubber mounts, if they are missing or worn out (they can be used to fasten the motor to the furnace and reduce the noise).
- Add sound insulation to the unit. Melamine foam can do wonders if you install it right next to the blower intake (use steel wire to secure the construction).
How Long Do Furnace Blower Motors Last?
Your blower motor is going to last anywhere between 10 and 20 years. If you are lucky, the part will have the same lifespan as the actual furnace.
However, proper maintenance is the main key to a long and happy life.
- Ensure that the air registers are free of blockage and change the air filter on a regular basis.
- Lubricate the motor annually and change the belt, if needed.
- Every few months check the fan blades for cracks and missing balance weights. Clean the blades, if necessary.
Related: How Often You Should Change the Furnace Filter
Invite a professional to perform an annual inspection that should include a thorough visual inspection, an insulation resistance test, and voltage and current checks.