When the days become shorter and the temperature begins to dip, your furnace will start running a lot more – and that’s when we usually notice that something isn’t right with it.
One indication can be an unsettling noise that accompanies the warm heat that the furnace kicks out – it could be squealing, humming that is louder than usual, rattling, banging, whistling. That noise is most likely your furnace blower.
When your furnace is running, the noise that generally accompanies it comes from the blower pushing the warm throughout your home via the ductwork. Although the noise is annoying and can tend to keep you from sleeping soundly, there is hope. You can reduce or quiet that bothersome furnace blower noise by using a number of different methods. Read on to learn how to make your home a little quieter and more comfortable.
This is a furnace blower troubleshooting guide. It gives you places to look with a few tips on solutions to potential problems.
Unlike many Pick HVAC troubleshooting and FAQ guides, this one is broader rather than deep. It’s a good source of information for DIY homeowners who have basic knowledge of “where to go from here” once a potential solution has been identified.
Why is My Furnace Blower So Loud?
There are many different types of sound that may be coming from your furnace burner. Each sound has a reason and a remedy for the problem. Below are some common unwanted noises that may be coming from your furnace blower:
- Rattling Sound - This type of sound usually comes from something in the blower vibrating. The problem is most likely that a part has become loose or disconnected.
- Low Rumbling Sound - A rumbling sound may sound like it is coming from the blower motor, but it is probably caused by the burner or fuel ignitor not working properly. If you hear a rumbling sound, you should ask an HVAC technician to come out, diagnose the problem, and fix it. Or you can check out the PickHVAC page on Cleaning a Furnace Burner to see if that solves the issue.
- Banging Sound - A banging in the furnace may also happen with some whistling or “air-leaking” sound. This usually happens when there is a problem with the vents, ducts, or filters. You can check and clean the areas, or you may need to have a different size duct installed.
- Scraping Sound - If you hear something that sounds like metal on metal rubbing or scraping, you most likely have an issue with your motor mount or a loose pulley. You can check this while your furnace is running. Once you find what is causing the sound you can most likely replace the faulty part yourself.
- Squealing Sound - A high-pitched sound generally means that there is a loose belt. If the belt isn’t the issue, then you most likely will need to oil the motor.
Why is My Furnace Blower Making a Humming Sound?
One of the most common noises that may emanate from your furnace blower is a humming sound. This type of sound can come from many different sources, such as the fan/blower, transformer, or capacitor. If the issue is the capacitor, you can replace each part relatively easily without much cost. If the humming sound is due to the fan, then you can clean the fan to fix the problem.
To determine which, if any, of these issues is the source of the humming, remove the access panel or panels, and observe the system while it is running. You might have to depress a safety switch that pops up when you remove a panel.
The blower assembly is easy to identify – the large, round housing with the blower running inside it. The capacitor is located on the outside of the assembly – a round or oval “can” with wires attaching it to the blower assembly. If you can identify what’s causing the noise, it will guide your next steps. Our page on Capacitor Replacement makes this job easy, and the part is cheap.
If it is the blower, there are tips for quieting a furnace blower below. Basically, it might just need a good cleaning and some lubrication. Or it might need bearing replacement or total assembly replacement – but that’s rare. This article offers a deep dive on furnace blower assembly cleaning.
If the humming sound continues after you cleaned the fan or replaced the capacitor, then you should call an HVAC technician to diagnose and repair the problem.
How Can I Reduce the Noise Coming from My Furnace Blower?
There are many different solutions to reducing the noise that is coming from your furnace blower. Some are very easy fixes that the average homeowner can accomplish, and other solutions are a little more difficult. Some of the solutions may require the hiring of an HVAC technician or maybe a contractor. Below are the most effective ways to quiet your furnace blower:
- Adjust your fan speed - When your furnace was installed, the HVAC company should have set your fan speed to work perfectly with the type of furnace you have and the size of your home. However, this isn’t always the case. It might be running too fast, which in itself can cause the noise, or the speed of the blower might be pushing too much air into the supply duct, causing it to hum. Adjusting your fan speed can help eliminate the noise coming from your blower.
- Deep clean your blower fan - Check your blower fan for dust build-up. Too much build up will cause an annoying humming sound. Using a brush and a mild cleaner, fully clean the blower fan blades.
- Replace the bearings in the blower fan - Over a period of time, the bearings in the fan can and will begin to fail. This will cause unwanted noise to emanate throughout the ductwork. Simply replacing the blower fan bearings can eliminate excess noise.
- Check the fan blades - Although it isn't very common, the fan blade can bend. This will create unwanted noise from your blower.
- Oil the motor - Using 3-in-1 motor oil, lubricate the motor’s axle. Some blower assemblies have little plastic caps on each end that can be removed, and a few drops of oil can be squirted into them. The guy in this video doesn’t really know what he’s doing – but it is instrumental in that you can see the caps at about 6:30 of the video. Unfortunately, he ignores the caps (and catches a lot of grief for it in the comments). Lubing the motor might stop any screeching and high-pitched sounds. If the bearing is bad, the fix might be temporary, but it is worth a shot or two of oil
- Inspect the belts - The belts on the motor can become frayed, cracked, or even break. Replace any belts that are in rough condition. If they’re slipping, they’ll whine for sure, like a slipping belt on your vehicle.
- Secure the motor mounts - Since the motor on your blower fan is constantly in use, this can cause the mounts to become loose. A vibrating motor will cause a lot of unwanted noise. Simply check where the motor is mounted and tighten the connections to make sure it is securely fastened to the furnace.
- Motor replacement - If the motor is making an unusual knocking sound, this could indicate that the motor may need to be replaced. Unfortunately, this is an expensive fix, but is necessary to ensure that the furnace is functioning properly.
- Insulate – Sometimes motors are just loud even when running “perfectly.” Use insulation around the furnace blower, a very simple and fast way to dampen any unwanted noise that may come from your furnace blower. Another option is using acoustic panels attached to the outside of the furnace cabinet to help lessen the noise.
- Fill gaps in the ductwork - Using a sealant that is made for soundproofing, that is heat resistant, fill in any gaps that are present in the ducts. If you’re inspecting the furnace and realize it is the ductwork making the humming noise or other bothersome sound, then finding and repairing gaps or fully wrapping your ducts with insulation will reduce noise and make your ductwork more energy efficient.
- Replace or clean the filters – Dirty filters cause a whistling or humming noise. Replace yours before they get to this point for efficient furnace operation that doesn’t put too much strain on the equipment.
Having a noisy or loud furnace blower is very annoying and may cause much frustration, but there are many specific reasons why your furnace blower is being too loud. Use the information above to find out why the sound is occurring. Once you have diagnosed the issue, you can troubleshoot and fix the problem by using a variety of methods to quiet your noisy furnace blower.
As always, if you have any trouble and are struggling with making your furnace blower quieter, you should reach out to your local heating and cooling experts to help eliminate the problem.