“Bang… bang… bang”… who could that possibly be? Oh yeah, it’s the damn furnace! A noisy furnace is a regular and very annoying part of many homes. Whistling and squeaking sounds are also very common. There are a few well established reasons for furnace noise and ways to fix them.
1. Fix weak spots in the dents – for banging sounds during start up
The first common reason for furnace “banging” noise is oil-canning or buckling from the pressure of some part of the duct work. Some also equate the noise with “thunder”. You can fix a weak spot in the ducts by screwing a thicker piece of metal on it.
Denting a weak spot with a hammer can also fix the issue, but it’s better to go with the first option, especially if you’re less experienced with this type of work so as not to cause more damage.
Gas ignition malfunction, also known as “roll-out” can be another (and more dangerous) source of noise. This is basically a small explosion or a larger burst of flame that happens when the furnace starts up.
So in order to know if this is the problem you’re dealing with, watch through the furnace doors when it starts up. If you can’t see through the doors, simply listen and try to pinpoint where the sound is coming from. Another symptom that indicates ignition malfunction is if the doors of the furnace shake.
If the shaking happens, try again with the door of the burner compartment open. If there are extra flames or shaking happening at the same time as the noise, then you’ve got a more serious problem on your hands.
I suggest calling a professional because this can be a dangerous situation for your home. Especially if you have an older furnace. Most of the newer furnaces have a roll-out sensor that shuts down the unit if problems with ignition occur. So this is not as common as a weak spot in the dent work. But it’s better to be safe than sorry and get it fixed as soon as possible if it’s indeed what you’re dealing with.
2. Improve air flow to stop whistling and whooshing sounds
Whistling noise from the furnace can have multiple sources. But the main cause is almost always the same – reduced airflow.
If the whistling started only recently, you’re probably dealing with a dirty filter. If the filter is clogged it’s going to have a harder time sucking the air. As it sucks air through small holes it produces the whistling noise just like a puckered mouth.
You can check if the filter is causing the whistling by pulling it out. If it’s the problem the whistling will stop. So if the filter is indeed dirty and preventing air flow, simply remove it and order a new one. It’s better than leaving it inside as the reduced air flow can otherwise damage the fan motor.
If the filter is not the problem, check out the duct for gaps. Gaps may be present in the space where the duct connects with the furnace, close to the blower. In that case you’ll have to seal the gap. To do this you can use duct tape, foil tape or even better, hi-temperature silicone.
If neither excessive dirt in the filter or gaps in the duct are present, then you’re probably dealing with ducts that are too small. So when you remove the door from the furnace, the whistling will stop because there will finally be enough air coming through. Ducts that are too small will require resizing or replacement to improve the general air flow, or the whistling will continue indefinitely.
Whooshing sounds are also a result of bad airflow. It happens as the hot air passes through the registers in and out of the room. In that case also resizing the ducts will usually fix the problem. Alternatively, you can use a cheap permeable filter with more and bigger holes to increase air flow.
3. Tighten loose parts to prevent rattling and vibrations
Rattling and vibrations are almost always due to loose parts. Loose ducts more specifically. You can fix the rattling noise by adding more screws to the ducts. Or you can tighten the loose parts with duct-tape. And if the furnace sits on a hard surface like concrete it will create more vibrations.
So if you can place some soft material under it, it can definitely help. I suggest using rubber pads. Even a 1/4 inch thick rubber pad can help reduce the vibrations, and that’s probably the thickness you should go for in order to place easily.
4. Secure the duct work to get rid of squeaking noise
Squeaking noise from the furnace when you’re walking is due to poorly secured duct work on the ceiling below. Usually the duct is too tightly secured, or the metal part wasn’t nailed correctly. In that case, try reinforcing or rehanging the duct to secure it properly. You’ll know that you did it right when the squeaking is no longer present.
5. Fix the bearings or the motor
You will generally be able to discern if the noise is coming from motor or not. It’s either due to a weak motor that sort of “bounces” while it’s working or its due to worn down motor bearings.
However, the bearings might just need to be lubricated. Some motors have plugs or caps that you can remove in order to place the lubrication oil inside. Other motors have a more intricate design so this won’t work for every model. Since you’re dealing with a heater after all, cause is advised if you attempt to do this on your own.
However, a dirty filter can also make the motor run faster and louder. So it’s important to clean the filters before worrying about other causes. In either case the best course of action is to call a professional to check the unit and see if it can be fixed or if the motor or the bearings should be replaced.
Here are 3 very useful videos on checking and potentially fixing the furnace blower motor:
VIDEO 2: How to fix a blower motor
A furnace will make different noises depending on where the issue is. Often the problem arises from reduced air flow. Either because of dirty filters or oil canning duct work. These two problems can be found even in relatively newer furnaces. Newer furnaces might also be badly installed, especially the duct work on the ceiling.
With furnaces that are a few years older, you could at that point be dealing with a faulty motor. If you’re a mechanic or someone who loves fixing stuff in your spare time, checking for faulty parts and fixing or replacing them can be a satisfying project.
For others who don’t have much experience, the best course of action is to call a professional. But even if you decide to hire a professional to fix the problem it would be useful to inspect the furnace first by using the tips from this article. Then you can at least approximate where the noise is coming from and what the problem might be.
It can save the pro some time and you as a client money as the work will be done in a shorter time frame. Hope this helps!