Why does my furnace make a loud banging noise?
Delayed ignition causes a small explosion of built-up gas inside the combustion chamber, resulting in a loud bang when the furnace finally fires up. This issue stops the heating system from operating smoothly and requires immediate attention to prevent damage to the equipment during freezing weather.
What the numbers show
Counted from the threads quoted below. How we count
- The most recent one is from November 2026.
- This comes up 22.5× more often in r/hvacadvice than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1Turning off the gas line and power to the furnaceDid this help you?
- 2Using a space heater and extra layers to stay warmDid this help you?
- 3Waiting for an emergency technician to come outDid this help you?
- 4Switching off the heating systemDid this help you?
- 5Lowering the pump speed settingDid this help you?
- 6Replacing the pump or its bearingsDid this help you?
- 7Wearing noise-cancelling headphones and hiding upstairsDid this help you?
- 8Turning the HVAC system completely offDid this help you?
- 9Consulting multiple technicians, an independent HVAC company, and a retired HVAC engineer for competing diagnosticsDid this help you?
- 10Calling the installer to check it under warrantyDid this help you?
- 11Taking the front panel off while it runs a cycle to identify the issue betterDid this help you?
- 12tweaking the offside bracket that holds the heat exchangerDid this help you?
- 13adjusting the gas piping and burner assemblyDid this help you?
- 14waiting to see if the new unit settles over timeDid this help you?
- 15Recording a video of the noise and asking for advice on internet forums before calling a technician.Did this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Gas line and the power to the furnace have been turned off. 15” of snow expected. Looks like we are face tanking this with a space heater and some layers.”source ↗
“Got this picture before I turned it off. It starts up normally when you turn on the thermostat, but after about an hour it repeats this process over and over again.”source ↗
“When the system ran in low stage furnace heat and especially in high stage heat, there was better airflow, but a very loud humming sound that revs up as the furnace blower ramps up.”source ↗
“The noise has been unbearable for me, not out of sheer decibel levels (around 50-55 decibels 1 floor above furnace room that is in basement), but the specific humming sound independent of the airflow noises from the ducts. It also vibrates the entire wood floor kitchen above furnace room as well.”source ↗
“What is interesting to me is that if I fully remove the filter temporarily. The humming noise disappears in both low and high stage testing.”source ↗
“i'm looking for some advice on the best product/method to fix a loose connection on my high- efficiency furnace.”source ↗
“The black air intake pipe where it connects directly into the burner box/gas chamber housing has come loose. Because of the draft inducer fan suction, the pipe is currently vibrating and shaking pretty loudly against the housing when the furnace runs.”source ↗
“The connection has just slipped/loosened up over time rather than cracked”source ↗
“I noticed the new unit making this loud rumbling noise coming from the outside pvc tubing that it didn’t make before with the old unit- granted, we haven’t had our heater on for probably 5 months.”source ↗
“Not from what I can tell, I only noticed the noise because I was walking by the back door where the pipe is and when I opened it that’s when I realized how loud it was coming from there”source ↗
“I noticed that the vents are whistling a bit but also that the furnace and its vents are vibrating, enough that it can be felt and seen.”source ↗
“Brand new UDXC45 reznor making loud popping sounds after blower kicks on during call for heat as heat exchanger warms up. It then dissipates and returns on cool down once blower removes heat and heat exchanger cools down.”source ↗
“Have tried tweaking the offside bracket that holds heat exchanger and adjusting gas piping/ burner assembly all to no avail.”source ↗
“Right, curious because I didn't hear the banging on expansion and contraction from Mr Heaters and Sterlings, but this Reznor seems to do it quite loudly beyond the standard rhythmic popping.”source ↗
“Every time my furnace runs, the red device( a motor?) produces a loud noise as in the video, is it normal to be this loud? Or do I need to ask someone over to take a look?”source ↗
“it creates a constant hum all day, everyday 24/7. What can I do to make it quieter? It's quite hot and so not sure if I can wrap it in anything. I'm quite noise sensitive and it's vibrating constantly giving noise in my bedroom and living room and I just want some peace and quiet, without having to switch off my heating system (it's an older house 70's).”source ↗
“Can confirm it was on speed 2, dropped to speed 1 and still relatively loud, so assuming the bearings have gone.”source ↗
“Yeah it's still noisy on 1 so I'm assuming it's the bearing, we are having work done on the house soon so will get that replaced as part of it, thank you for all your help!”source ↗
Where this came up
People with this problem also raised
- 2Furnace making a humming noise even when it is not running
- 3Why is water pooling inside my furnace?
- 4Why is my boiler making a constant humming noise when heat is on?
- 2Furnace making popping sound and flame flickering
- 21Why is my new dryer vibrating and buzzing?
- 3Propane boiler making puffing exhaust noise in extreme cold