As the weather gets colder, many people are turning on their furnaces for the first time since last winter. If you’re having trouble getting your furnace started, read our list of reasons why your furnace won’t kick on, or contact us for furnace repair services if those tips don’t clear up the problem.

Once you get the furnace turned on successfully, it might start making a racket. There’s no such thing as a truly silent furnace, so some furnace sounds are normal. But what’s happening behind the scenes that’s causing all the strange noises? And what do they all mean?

Are you desperately trying to understand what your furnace is telling you? When are furnace sounds normal, and when do they indicate you should get your heating system serviced by an HVAC technician? Don’t fear the growling beast in your basement. We’ve broken down common furnace noises into three categories: Normal, May-Need-Service, and Contact-Service-Technician-ASAP. 

Note: Even if you don’t hear any alarming sounds, it’s still important to have your furnace regularly serviced so essential parts like the air filter can be replaced and renewed. This keeps your furnace in ideal shape. Now, back to those noises!

Normal Noises

Humming 

Almost all furnaces hum when they are switched on. Humming at a low level is a typical furnace sound that happens when the furnace is operating.

Occasional hissing

If you have a gas furnace, an occasional hiss is another sound you might hear. It is impossible to stop all air escaping from a furnace, and that is where a hissing sound might come from.

Quiet crackling/popping during startup or shutdown

During or after the furnace startup or shutdown process, you might hear some crackling or popping sounds. These sounds are normal — what you hear is the sound of metal expanding and contracting, both in the furnace and potentially within your air ducts.

May-Need-Service Noises

Loud and irregular popping

A loud and irregular popping noise that keeps happening even after the furnace has been running for several hours can mean your air ducts aren’t sealed properly. You might need to contact a technician to make sure your system is as efficient as possible.

Thwapping

If your furnace sounds like there’s something thwapping inside of it, there may be a problem with the blower wheel. The wheel may be faulty, dirty, or jammed, or something might be stuck inside the wheel itself. Running the furnace with reduced blower wheel capacity creates increased wear and tear on the furnace, shortening its lifespan. It’s also less effective for your heating system, costing you more money and time.

Chirping

Some furnaces chirp for a short period when they are starting up and beginning to work, but a consistent chirping that lasts the entire time the furnace is running may indicate a loose screw, a bearing that needs oil, or dirt buildup within the furnace. Consider calling a technician as chirping can be the first sign of a problem with your furnace.

Clicking

Repeated clicking, often accompanied by delayed or faulty furnace startup, can mean that your furnace is trying and failing to work effectively. Often, a clicking sound happens when the spark igniter within the furnace tries and fails to light the burners. This may be because of dirty burners or a faulty gas valve. Not only does this inconvenience you when you’re trying to start heating your home, but it can also mean there could be a day coming soon when your furnace fails to light at all, leaving you with no heat.

Contact-Service-Technician-ASAP Noises

Persistent rattling

Sometimes a furnace can be rattling because a single screw needs to be tightened or an air duct joint is a little loose. But a rattle can also happen because your heat exchanger is damaged. The heat exchanger is an essential part of your furnace and will need attention right away. Something else that might cause your furnace to rattle is an object caught in your heating ducts, which is a fire hazard. While a rattle might seem like a minor concern, it’s not wise to gamble your chances.

Bang/“gunshot”

It’s easy to be alarmed by a sudden “boom” from your furnace — and you’re right to be alarmed. There’s a chance that this furnace noise could come from gas buildup from delayed ignition or a hole in a crucial valve within the furnace. Contact a professional immediately; you don’t want to mess around with the risk of explosion.

Squealing or screeching

Squealing or screeching might mean your furnace’s motor is malfunctioning or that the furnace’s parts are degraded or outdated. Whichever reason, it is an indication that your furnace’s life might be coming to an end if you don’t get it serviced.

Scraping

The sound of metal on metal is a big red flag. It might be another sign of the motor failing or separating from the motor mount. It could be two loose parts rubbing together and wearing on your furnace as a whole. Regardless of what could be causing scraping sounds, it’s time to turn off the furnace and call an HVAC technician.

Clunking

Clunking can happen when a belt is damaged, cracked, or has slipped. The system cannot function properly without a working belt. Contact a professional before more damage is done.

Rumbling/aggressive vibration

If your furnace sounds like a Harley Davidson or begins vibrating aggressively, turn it off and contact a professional right away, especially if it’s gas-powered. This is likely due to a leak in your heating exchange. If you have a gas heater, this can cause a deadly carbon monoxide leak.

Reliable heating is crucial in Minnesota as we regularly endure sub-zero conditions throughout most of the winter months. Furnace repair services are an essential part of making sure you can get through the brutal winter cold. Schedule an appointment with us today and get back to being comfortable!