Why does my furnace sound like it's backfiring?

Author: Mr. Enoch Lockman III  |  Last update: Wednesday, August 20, 2025

There are a few different answers to the question about why a furnace sounds like it's backfiring, though. The most common answer is that the age of your furnace may mean that worn down parts are causing gas to backup in a way that eventually leads to a sudden release and boom.

What would cause a furnace to backfire?

If a boiler or heater is not running properly, unburned fuel may accumulate in its combustion chamber. Upon starting the heating appliance, this oil can ignite and cause an explosion or misfire inside the furnace.

Why does my furnace sound like it's popping?

Popping. If you hear popping sounds and you don't have a bag of popcorn in the microwave, you could be dealing with dirty furnace burners or damaged air ducts. When the burners are dirty, the buildup prevents them from igniting, which causes too much gas to build up, making a popping sound.

Why is my furnace making a pulsing sound?

Steady Pulsing

The sound can also happen if some components of the HVAC system, such as a fan blade or coil, are loose. Insulate your HVAC system to prevent touching between the walls and refrigerant lines. A professional can also tighten any loose parts in the HVAC system to avoid pulsating noises.

Why is my furnace making a boom sound?

If you are hearing a boom sound coming from your furnace, the combustion chamber and burners can become clogged from grime and build up.

Explosions During Furnace Ignition - Symptom of Bad Heat Exchanger

When should I worry about my furnace noise?

Loud Bangs, Rumbles, Knocks, or Booms

Loud noises like this are a sign of a build of gas in a furnace. The noise you hear can mean your heat exchanger is at risk of cracking. Even worse, it's a sign that something dangerous could happen if you continue to use your heater.

Why does my heating make a banging sound?

The radiators in your home are connected by pipes that are controlled by valves. Partially closed radiator valves in a steam system may be trapping condensation in your radiators instead of allowing it to flow back to the boiler (i.e., return), which can cause a banging noise when new hot water enters the radiator.

What does a failing furnace sound like?

Thumps and bumping noises, like an unbalanced washing machine, often indicate an unbalanced blower wheel or motor. This is a serious issue that requires immediate HVAC repair. The blower wheel and motor are major furnace parts and you don't want them bouncing around.

What does it sound like when a furnace is going out?

We're here for the long run. So if you hear a squeal, a new click, grinding, or popping when your furnace is at any point in the heating cycle, it's best to have a tech take a look and catch things early.

Why is there a loud thump when my furnace turns off?

Replace a dirty filter

Once the furnace cycles off, the homeowner will hear a loud banging noise as the metal in the furnace expands due to the excess air. Regularly cleaning or replacing air filters prevents excess dirt from building up.

How do I stop my furnace from popping?

Here are two ways to solve the problem:
  1. Seal and insulate your ducts. Wrapping your ducts in insulation should solve your “cold winter morning” heating duct popping noise. ...
  2. Replace your ducts. Replacing your ducts is usually more cost effective than insulating them.

Why is my furnace so loud all of a sudden?

If your furnace suddenly produces loud, sudden banging or booms, you should call an experienced technician as soon as possible. These sounds could indicate stuck ignition, a potentially dangerous situation involving carbon monoxide which is deadly.

Why is my HVAC unit making a popping sound?

When ducts are too small, it can create a buildup of pressure in the system, which results in a clicking or popping sound. These noises can occur when the heating or cooling unit turns on or off, and sometimes persist throughout the cycle of the HVAC system.

Why does my furnace keep making a popping sound?

The blower in newer furnaces is much stronger than older models, leading to the contracting and expanding of the ductwork attached to it. As the motor kicks on, you'll hear this popping as the metal ductwork expands to accommodate the strength of the blower.

What is the most common cause of backfire?

Backfires and afterfires are worth paying attention to since they can cause engine damage, power loss, and decreased fuel efficiency. There's a variety of factors that can cause your car to backfire, but the most common ones are having a poor air to fuel ratio, a misfiring spark plug, or good old-fashioned bad timing.

Why did my furnace backfire?

Dirty or faulty igniters, weak pilot lights, or improper gas pressure are often the cause of ignition backfires in high efficiency gas furnaces.

Why do my ducts make a popping sound?

Ductwork responds to pressure changes at times by making popping noises. This is normal, so you shouldn't be alarmed if you hear it at times. That said, when air duct leakage lowers the pressure or a blocked vent raises the pressure, you may end up with more serious problems that need addressing urgently.

How much does a new furnace cost?

You should expect to spend between $3,800 and $12,00 on a new furnace, including both the unit and installation costs. Factors influencing the price include the type of furnace (gas, electric, or oil), the unit's efficiency rating, and the complexity of the installation.

How much does a furnace blower motor cost?

While costs can vary, homeowners can typically expect the following range: Standard Blower Motors: These might cost between $400-700, excluding labor. Advanced Multi-Speed or Variable-Speed Motors: These are generally more expensive, with costs ranging between $650-1250, not including labor.

What is the most common furnace failure?

One of the most common furnace problems is a malfunctioning thermostat. A sure sign your thermostat isn't working properly is if your fan is constantly running. This will cause your thermostat battery to run, and cause your furnace to work inefficiently.

What does it mean when your furnace booms?

Booms & Bangs

When too much gas builds up in the combustion chamber and the ignition is delayed, your furnace experiences a small gas explosion. This can be caused by low gas pressure, clogged burners, and dirty equipment.

Why does my heater make a thump sound?

A loud, regular thump or thud that sounds continuously as your furnace is running is probably an unbalanced blower wheel or motor. You'll hear the sound of the rotation as the wheel or motor whirls unevenly in your system. You should have the part balanced as quickly as possible to avoid further damage.

How do I stop my furnace from banging?

Clean Any Dirty Burners

The bang that you hear is the sound of a larger volume of fuel finally igniting, creating a small explosion. This issue is called delayed ignition. If you suspect delayed ignition is producing the banging noise you hear, you'll need to clean your burners to stop the furnace from banging.

Why does my house make a weird banging sound?

Most often, it's your home's plumbing system. It may be due to fluctuating water pressure issues, loose plumbing pipes, or a faulty valve. To help find the problem and solve it, the first thing you need to do is take note when you hear the banging noises.

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