Furnace Makes Banging Noise When It Shuts Off? (What It Means)

It is normal for a furnace or air conditioner to make noises, but it can be disconcerting. Banging sounds that come from your furnace are common, but that doesn’t mean that it’s a good thing. So, why is it that your furnace makes a banging noise when it shuts off?

A furnace makes a banging noise when it shuts off if the ductwork is dirty or clogged. Clogged ducts or a dirty air filter cause hot air to back up which increases the pressure within the system. Temperature changes, dirty fan blowers, and a loose actuator can cause your furnace to make banging noises.

It is important to clean your furnace filter 3-4 times per year so that your furnace will function as intended. Banging noises when your furnace shuts off don’t always indicate a serious problem, but it’s important to inspect several components. Follow along as we explore what it means when your furnace makes a banging noise when it shuts off.

The actuator is an important part of your furnace that helps push air through the system. It is common for a furnace actuator to come loose during operation. You will hear it bang around when your furnace shuts off if it is loose.

Luckily, all that you need to do is adjust your actuator if it is loose. The actuator is located above or below the coil depending on your furnace. Tighten the nut on the actuator dampers with a pair of pliers so that it doesn’t knock and bang around.

Clogged ductwork is unhealthy for an HVAC system and can explain why your furnace makes a banging noise when it shuts off. Hot air can back up and cause the pressure to increase within your ductwork if there is a lot of debris. The combination of heat and pressure can create a banging noise when your furnace shuts off.

First, you must remove and clean the vent covers so that you can access the ducts. Knock the dust loose with a long tool such as a broom handle or even a drain snake. Vacuum the rest of the dust and debris with as long of a vacuum hose as you can find.

This may not be doable for every homeowner, and that’s why it’s a good idea to hire a professional. Clogged ductwork can increase the risk of a fire hazard and worsen the air quality in your home.

Your furnace’s fan blower can get clogged just like the ductwork and air filter. This blower is important because it circulates air for your furnace and air conditioner. HVAC professionals recommend that you clean the blower fan every 2 years so that it can function properly.

Otherwise, you will hear it bang and knock when your furnace or air conditioner shuts off. Make sure to shut off power to the system before your clean your fan blower so that it is safe to work with. You must remove the panel and pull the blower out so that you can clean it.

Avoid disconnecting the wires so that you can easily put the blower back where it was. Clean the blades with a small brush and clean the blower housing with a cloth. You can clean the blower housing with a vacuum if it is particularly dirty, and your furnace should stop making a banging noise when it shuts off.

A dirty filter can cause your furnace’s performance to suffer in many ways. Dirty filters can even cause your furnace to make banging noises when it shuts off. Filters can easily clog when they become dirty which can block the airflow.

The backup of air from a clogged filter can increase pressure within your furnace’s ductwork. Eventually, the increased pressure and temperature will create knocks and bangs that ring out throughout the furnace. Change your furnace filter 3-4 times per year to avoid HVAC problems.

Ideally, you should change your furnace filter at the beginning of each season or sooner if it is dirty. Dirty filters force your furnace motor to work extra hard to make up for the clog.

Temperature changes can cause several components, such as the ductwork, to expand and contract. Pressure within your furnace and ducts will fluctuate when the temperature changes. You will notice buzzing, humming, and banging noises when your furnace shuts off or runs in many cases.

Banging noises are common when your furnace shuts off if you live in a hot and humid climate. The spring and summer are known for rapid temperature changes, especially if you live in a hot or tropical zone. In this case, there is nothing wrong with your furnace if it makes a banging noise when it shuts off.

You can narrow the banging sound down to temperature changes if you inspect your HVAC system. Temperature changes are to blame if your furnace filter and ductwork are clean and the actuator dampers are in the proper position.

Related Questions

Why does my furnace make a banging noise when it turns on?

We now know why there may be a banging sound when the furnace turns off, but what about when it starts up? When there is a delayed ignition in the furnace, it can cause a sharp boom or bang to be heard as the burner cycles itself on.When running normally, the electric igniter or pilot flame should ignite the gas as it flows through the open gas valve. If it takes a moment to produce, the excess gas can result in a loud banging sound inside of the furnace cabinet.

Can a gas furnace explode?

While it is possible for a gas furnace to catch fire or explode, it is very unlikely. If there is any danger than an explosion might occur, the furnace will typically turn off automatically, as they are designed to do so. If you have a quality furnace and always perform the necessary routine maintenance, you should never have to worry about explosions or fires.