If your furnace makes a loud noise when it kicks on, there is likely something wrong with it or the ducts it is connected to. What exactly is going on? It depends on what kind of noise you’re hearing. We’ll cover the most common noises, from buzzing to rumbling, and there most likely causes of those noises below.
1. Banging Noise
If your furnace makes a loud bang a few moments after you turn it on, stand near your furnace and try to hear where the noise comes from. If it’s not from the furnace, but from the ducts nearby, this problem is called “oil-canning.” The ducts are simply popping because of the pressure change. This isn’t a serious problem, and you can fix it by securing wherever the popping is happening with additional screws or duct tape.
If instead the banging noise is coming from the furnace itself, you likely have a more serious problem called an ignition roll-out. Usually, this problem has the furnace shake or causes a visible flame. The gas is building up before it ignites, causing a larger ignition than is safe. This is a safety issue and needs to be addressed by an HVAC professional.
2. Rumbling or Grinding Noise
Instead of one sudden bang, your furnace could let off a rumbling or grinding noise for a few moments when it first comes on, or for the entire time, it’s on. Normally this kind of sound is two mechanical parts of the furnace grinding against each other. If this is the case, these two parts will wear out quickly, so unless you have a professional find and correct the problem, you could end up needing a whole new furnace soon.
Although, if it sounds more like a rumbling than grinding, and you can see the ductwork moving, it could just be the echo made from unsecured ducts. If so, your ducts will need to be secured. It’s possible that they’ve come loose because they’re the wrong size for the amount of forced air your furnace pushes through. If so, you’ll need an HVAC professional to replace the vents.
3. Whistling or Buzzing Noise
If you hear a high pitched whistling noise, kind of like a kettle, when your furnace turns on, it’s likely that you have a small hole somewhere in the system that is releasing the forced air the furnace is trying to move through your home. If this is the case, you will need a professional to solve this problem. Simply patching the hole with duct tape won’t work for long. Eventually, the air will force it’s way out again. And, once it does, your furnace will be less efficient.
4. Rattling Noise
A rattling or vibrating noise is most often made from loose ducts. Just like with the banging noise, you just have to find where the noise is coming from and secure the loose ducts with screws or duct tape.
If you add screws and duct tape to your vents but the noise doesn’t stop, its likely time to call in a professional. While this short guide covers the most common reasons for your furnace to make a noise, there’s a lot more than can be going on. When in doubt, call an HVAC specialist.