Any electrical material will make some noises during operation. Similarly, it is common for a furnace to make a low noise when operating. But, the problem occurs when you hear loud, alarming noises from the unit.
Noisy furnaces indicate a faulty blower motor or heat exchanger, dirty burners, loose furnace parts, faulty transformers, or bad inducers. Buzzing, banging, chirping, rattling, and whistling are common noise types. If you notice any irregular noise, you should check for possible problems.
The number of reasons and noise type is more. This guide will explore the different noise types and the reasons behind them. We will also share a few preventive measures to avoid the noise.
Common reasons include the following:
1. Loose blower wheel
A blower wheel is a part of the blower motor.
It moves the warm air into the ducts of your house.
The blower wheel may disconnect from the motor shaft due to dirt buildup in the air filters and release a loud rubbing noise.
The dirt moves towards the blower wheel, and the wheels rub against each other’s internal parts.
The wheel struggles to release the warm air out of your furnace.
The strain will detach the wheel from the motor shaft and create a rubbing noise.
- Turn off the furnace and open the blower chamber.
- Find the blower wheel and tighten any loose screws at the blower shaft.
- Close the chamber and turn on your furnace.
Wait for some time to see if the furnace works. Otherwise, call an HVAC expert.
2. Broken blower wheel
While checking the blower wheel for loose connections, unscrew the wheel from the shaft and check it thoroughly for damages.
A broken wheel could also make rubbing noises.
You must replace the wheel if it is cracked.
You must hire an experienced HVAC expert to deal with this matter.
The expert will analyze the system, find a suitable wheel, install it properly, and suggest ways to keep the new one in good condition.
3. Worn-out blower motor bearings
The blower motor bearings on the shaft allow the armature to spin without friction.
The bearings will require annual lubrication.
If the furnace overheats, the lubricant in the bearing will break down and make them rub against each other, creating a rubbing noise.
Dirty air filters are another reason behind the overheating.
Lubricate the bearings every year.
Use non-detergent motor oil for each port and the blower shafts too.
Do not over-oil them.
Some blowers will have grease cups instead of oil cups.
Find the grease cups and refill them with a bearing lube.
If the motor bearings have worn out too much, lubricate them slightly and keep them ready for replacement.
Use only 10-weighted non-detergent motor oil for lubrication.
Do not use more oil. Only 3 to 4 drops should suffice.
Whistling, banging, and popping noises
A furnace could make banging and popping noises due to the following:
4. Clogged or faulty air filter
Furnaces suck in the surrounding air to treat and release them as warm air.
This air contains many dirt particles.
The dirt particles get trapped in the filter when the furnace sucks them inside.
Over time, the filter will become dirty, and you will receive less warm air.
The filter will struggle to give you enough air and create a negative pressure in the ducts.
Due to this, the furnace will have a whistling sound at first, which will progress to a banging or popping noise.
The same occurs if your furnace filter is at fault, for example, broken or cracked somewhere.
To must clean or replace the furnace filters every 3 to 4 months.
- Turn off the furnace and open the door.
- Remove the filter to check its condition.
- Replace the filter with the new one. If it is reusable, wash and dry it, and again put it back in place.
- Check the direction of the arrows in the previous filter removal to maintain it after replacement.
- Once cleaned, close the furnace door and start the unit.
Decide on the changing frequency based on the filter size.
5. Wrong-size ducts
Your furnace will make banging noises due to incompatible parts, for example, ductwork.
A wrong duct size will create pressure, and the unit will release a banging or popping noise.
Sometimes, the furnace will release a whistling noise due to small ducts at the beginning. Slowly, it can progress to a banging or popping noise.
Over time, the ducts will damage if you do not change them.
First, estimate the furnace size to get the right duct size.
Also, examine the air pressure the furnace puts in the duct.
If the pressure is too much:
- Replace the furnace with a smaller unit. But this might reduce the airflow in your house.
- The second option is to replace the ducts with bigger ones.
6. Dirty ductwork
When excessive dirt collects in the ductwork, you hear a banging noise from your furnace unit.
This dust will end up inside your house, and your family will experience breathing issues and allergies.
It is more dangerous for people with lung disease and asthma.
Remove the duck panels and clean them one by one with the help of a brush. Use a toothbrush for the corners.
After cleaning, fasten all the panels tightly. Loose panels may cause flapping noises.
7. Poor ductwork insulation
Ductwork is crucial for the HVAC system.
It has lines and vents through which the air is pushed from the furnace and spread into the rooms.
Insulation is necessary to prevent the air from escaping so that your house receives enough airflow.
Problems in the insulation or no insulation will weaken the ducts and allow the air to escape, releasing a popping noise.
First, ensure the problem by walking along the duct lines and vents.
It will let you know whether the air is escaping or not.
Call an HVAC expert to insulate the ductwork if you haven’t already.
If there is already insulation, but the air escapes (a popping sound confirms it), find the problem and reinstall the insulation.
You can use duct tape to keep the insulation in place.
8. Air escaping from the unit
Air escapes due to loose duct connections, increased air pressure, or loose register cover.
Air escaping can reduce heat efficiency and airflow and increase energy bills.
I have already shared about the ductwork in the previous points.
If the reason is increased air pressure, reduce the fan speed.
If the reason is a loose register cover, tighten the screws to secure the cover well.
9. Delayed ignition
When the ignition is delayed, the banging noise will come directly from the furnace during the ignition process.
The gas released into the unit produces fuel for the ignition.
The gas will gather in the combustion chamber when the ignition is late.
As a result, a large volume of gas will make a loud banging noise.
Address the problem immediately to prevent a mini-explosion inside the furnace.
There are some reasons behind this delay:
- Low gas pressure pushes gasses into the burners, allowing them to gather around the burners.
- A weak and dirty pilot light makes ignition harder, and the gas accumulates before burning.
- Dirty burners also accumulate gas before ignition, therefore delaying the process.
Call an HVAC expert to deal with these problems.
10. Faulty gas supply valve
Excessive pressure is applied to the gas valve when the furnace runs.
When the valves get damaged or loose, you will hear a whistling sound from your unit.
Check for loose connections or damage in the gas valves.
If there are any of these problems, fix them first.
If the valve becomes loose, tighten the screws.
If the valve is broken, replace it with the help of an HVAC expert.
While replacing, make sure that the furnace is off.
Otherwise, the valve will flow the gas at high pressure.
So, this can be dangerous.
Buzzing noises are the result of the following reasons:
11. Faulty wiring
In most cases, a buzzing noise means wire issues.
A furnace will contain many electrical wires, for example, a power source connecting the furnace’s interior, control board area, blower assembly, thermostat, and several other areas.
When a wire gets loose, you will hear a buzzing noise from your furnace.
Sometimes, it also indicates damage to the copper wire insulation.
Another reason is bare wires touching each other.
It also leads to fire hazards.
Access the furnace interior to check for loose wires:
- Turn off the furnace. Unplug if possible.
- Open the furnace door and look inside the compartment, especially around the wires. Check for loose or frayed wires.
- Check the insulation of the wires.
Call an HVAC expert to fix the problem.
12. Problem with the capacitor
The capacitor is close to the motor and helps to start the motor.
The capacitor is directly connected to the power source inside the furnace and will malfunction over time.
The capacitor may have several issues, like power surges, imbalance motor, etc.
Whenever you turn on your furnace, you hear a buzzing sound.
Check the capacitor for visual damage and loose wires.
If you find any loose wires, tighten them up.
For any physical damage to the component, check for its mounting or displacement.
Call a professional to test your capacitor with a multimeter if you still cannot find anything.
13. Faulty blower motor
The blower motor joins the capacitor to the blower fan.
Problems in the connection will lead to a buzzing sound.
A faulty or worn-out blower motor creates an endless buzzing or siren noise.
Sometimes, you may also hear a squealing noise.
You must confirm it by checking.
Check the motor to find out any wire issues or physical damages.
Connect the motor to an external power source to check for the buzzing noise. Replace the motor with the help of an HVAC expert.
14. Problem with the transformer
A transformer assures the starting of the furnace and regulates its voltage.
A low voltage will hinder the furnace’s functionality, leading to insufficient heating and airflow.
But when the voltage is too high, there will be electrical shortages and power surges, which can further damage the internal components and the control board.
As a result, your unit will release a loud buzzing noise.
Determine the reason behind the noise to solve it:
- The transformer allows too much voltage to pass to the furnace. You need an HVAC expert to check the transformer.
- The wires in the transformer are loose or faulty. Call an electrician to fix the wires.
- The box on the transformer is loose. Tightening the fastening will stop the noise.
Chirping and squealing noises
A furnace makes a chirping or squealing noise due to loose motor mounts or worn-out fan belts and bearings.
15. Loose motor mounts
Check the inside of the furnace once to check the motor mounts.
The mounts keep the motor in place and are fastened to the furnace’s housing with screws and bolts.
If the mounts are loose, it will create a chirping or squealing noise in the unit.
- Turn off the furnace at the breaker.
- Open the furnace door and look at the motor mounts.
- Wiggle the motor for loose mounts.
- Tighten the loose mount brackets, check the other mounts, close the furnace door, and start the unit.
If you still can’t solve it, ask for help.
16. Worn-out fan belts
Fan belts are used in the fan assemblies of the furnace to rotate the motor fans.
Since these belts constantly run when the furnace heats the air, they can wear out over time.
A worn-out belt becomes less efficient, reduces fan rotation, and decreases duct airflow.
It will also create a chirping or squealing noise whenever the furnace runs. The noise increases when the belt continues wearing out.
- Turn off the furnace.
- Open the main compartment to check the fan belts in all the motors.
- Look for damage signs like tears and holes.
- Check the thickness of the belt.
If the belt becomes thin or has damage signs, call an HVAC to replace it.
17. Worn-out bearings
The bearings help in the fan rotation and wear out over time.
As a result, your unit produces a chirping noise.
If you do not change the bearings, they will harm the motor assembly, and the sound will progress to squealing noise.
Sometimes, you could also hear rattling noises from your furnace due to loose motor set screws.
- Turn off the furnace.
- Check the bearings inside the furnace in each motor.
- Look for wear-out and damage signs.
- Call an HVAC to replace them.
Clicking or fluttering noises
A furnace will make a clicking noise if the heat exchanger has cracked.
18. Cracked heat exchanger
Heat exchangers are made of metal.
They move the heat from combustion to the furnace.
There will be cracks in the metal tube during constant heating and cooling.
The clicking sound would be from the metal that heats the cracks, starts expanding, and pushes against the exchanger.
A cracked exchanger will also leak carbon monoxide inside the house, which can be dangerous for your health.
If the exchanger is loose at the corner, tighten it correctly.
Call an HVAC expert to fix the heat exchanger.
Keep a carbon monoxide detector in your furnace room to get alarms about the CO leak.
The following reasons are responsible for the furnace’s rattling noise:
19. Dirty burners
When your furnace accumulates excessive dirt and debris in the burner, it will cause a rattling sound.
The sound will be loud if you don’t clean your furnace for over a year.
A dirty burner can also lead to a fluttering noise.
Check the blower and burner cavity for debris, and clean the blower fan and the back corners of the cavity.
Use a handheld, hose vacuum, or drain line to clean them.
Once cleaned, turn on the furnace to check its functionality.
20. Ducts wrapping and expanding
Periodic banging or rattling noise is due to the constant wrapping and expanding of the ducts after long-term use.
Though it is nothing stressful, the noise can be irritating.
Clean ducts make more noise.
The dirt and debris work as duct insulation. So, when you clean the ducts, the noise will be louder.
Insulating the ducts will reduce the noise.
21. Faulty draft inducer motor
The inducer motor clears the air in the heat exchanger and allows clean air inside the system.
Sometimes, the motor will become imbalanced or faulty, and you will hear a rattling or tapping noise from your unit.
When the inducer wears out, it will grow soot and make noise.
You need to replace the inducer motor.
Though you can do it yourself, it is best to hire an HVAC expert to replace it.
Cold weather straining the system causes knocking noises.
22. Cold weather
When you run a furnace in cold weather, a furnace works hard to give you the desired temperature.
In the process, the cold weather will strain the furnace and its machinery, which can, later on, produce a knocking sound.
The sound is normal and expected during low temperatures.
How to understand that the cold weather is stressing the furnace?
When you turn on the furnace, it immediately makes a tapping or knocking sound. But, the sound will vanish after some time.
There is no solution to this sound.
The sound will stop after some time or when the weather becomes normal.
Gurgling and dripping noises
Gurgling noises are mostly due to clogged drainage systems.
23. Blocked condensate pipes
The furnace uses these pipes to flow the condensation out of the system during the heating process.
If the pipes are blocked, the water pressure will increase in the condensate assembly, creating gurgling noises.
- Turn off the furnace and remove the condensate pipes from the trap.
- Take the pipes out and run some water to look for blocked parts.
- Take the pipe apart to find the blockage.
- Remove the blockage and put the pipe back.
- Consult an HVAC if you cannot do it.
24. Faulty condensate pump
You hear a gurgling noise when the pump is at fault.
The pump sucks the condensate water and sends it to drain outside the house through the pipes.
If the pump is faulty, the liquid will increase, make its way into the furnace, and create a gurgling noise.
If the water reaches the electronic parts, your furnace is at risk.
In most cases, you need to replace the pump.
Call an HVAC to replace it.
25. A problem in the refrigerant line
The problem does not apply to the heating system containing only the furnace.
Most houses have a full HVAC system comprising the furnace and AC.
The refrigerant lines in the AC cool the air and dehumidify your room.
Sometimes, the liquid gets stuck inside the line or leaks due to cracks.
When you turn on the furnace, the unit’s heat will produce a gurgling sound.
Check the refrigerant lines carefully for rust, erosion, or cracks.
Call an HVAC to fix it.
The expert will remove the remaining liquid, replace the tube, and refill it.
Make sure the tube is properly sealed. Otherwise, you will face the same problem.
Normal noises from the furnace
- Popping sounds from the ducts are due to the recent cleaning.
- A brief click during the starting of the furnace is due to the starting of the heating cycle.
- Chirping noises at the beginning of the heating season are because you started the unit after a long time. Dust builds up in your unit when you keep it off in summer. The noise will fade after a few days of running.
- Furnace Only Works After Reset: 9 Problem+Fix
- 15 Reasons Your Furnace Won’t Turn On (+Fix)
- 14 Reasons Your Furnace Won’t Turn Off (+Fix)
- 16 Reasons Your Furnace Is Not Heating (+Fix)
- 12 Reasons Your Furnace Is Blowing Cold Air (+Fix)
- 10 Reasons Why You Shouldn’t Run A Furnace Without A Filter
- 9 Reasons Your Furnace Is Short Cycling (+Fix)
- 11 Reasons Your Furnace Won’t Stay Lit (+Fix)
- 9 Reasons Why Your Furnace Shuts Off After 30 Seconds
How to prevent furnace problems?
- Clean or replace the air filters every 3 to 4 months.
- Clean the airflow obstructions.
- Perform regular maintenance of the furnace every year.
A furnace makes various other noises than those mentioned in this article, like groaning, rumbling, roaring, growling, etc.
But the reasons are the same.
So, you need to identify the noise, find the cause, and troubleshoot the problem.
If you are confused about it, call an HVAC expert to deal with it.