Your furnace is a mechanical thing, and you might expect its moving parts would make some noise when it’s running. However, there’s a difference between good noise – the nice quiet hum of motors running, fans blowing, and air moving through vents – and troublesome noise which makes you wonder if something is wrong.
If you’re noticing any of these strange noises coming from your furnace, it’s a good idea to contact a professional to inspect your equipment and see if something has gone awry.
Scraping sounds are never good. It usually means something is wrong with your fan and you should turn off your furnace right away to keep the motor from burning out. A foreign object may be obstructing the blower, or one of the blades may be warped or broken. Either way, it can cause big trouble.
A thumping noise in your washer means your load is out of balance. It can mean the same sort of thing when the thumping is coming from your furnace. A motor or blower wheel may be out of balance and that could cause big problems down the road for your mechanical equipment.
Gas and oil-fired furnaces sometimes put out a slight rumbling when they kick on, but if it is louder than usual or lasts longer than usual, this could indicate a serious problem with your burner. If you hear loud rumbling, turn off your equipment and call for service.
Clanking or rattling
Rattling could mean the fasteners to the metal housing of your unit have become loose, and those are easily tightened. If the rattling is on the inside, that’s another matter and you need to call a technician. Or sometimes twigs or other debris can get inside the fan of our outdoor unit and cause a little clanking or rattling noise. If you can see this is the problem, just turn off the power and remove whatever is rattling around. If you can see that the piece of debris has caused any damage to the compressor or fan, you should call a technician.
A common noise that occurs when you turn on a furnace at the beginning of the heating season is a loud pop when the fan stops and starts. This could simply be the sheet metal in your ductwork responding to pressure; it pops in as a reaction to the negative pressure of the fan, then pops back out when the fan shuts off and the pressure releases. It may be of no consequence, but a professional duct inspection could help you determine whether the noise is being caused by undersized or flimsy ductwork, or something else such as closed vents or a clogged air filter.
Escaping air can cause hissing. If it’s a light hiss, it could be caused by an air filter that isn’t installed properly or is the wrong size. Too many closed vents or furniture blocking air flow may also cause a hissing sound. If it’s a loud hiss, it may be the result of a leak somewhere in your ducts. This means a lot of expensively heated air that should be circulating throughout your house is being lost somewhere inside your walls, under the house, or in the attic.
A whistling noise is probably never a good noise when it comes to HVAC equipment. It could mean there’s a refrigerant leak in your condenser – or something else that’s causing a lot of internal pressure. If you hear whistling when you turn on your furnace, you should contact a technician right away.
Not all noise is bad noise, and even the occasional strange noise may merely mean it’s time for a tune-up. But any loud, disruptive, or continual noises can indicate a real concern and you should call a local furnace company like Drake Heating & Air to come take a look. They’ll be able to tighten or lubricate parts, replace belts and filters, or discover a problem before it becomes a huge repair or a danger to your safety.
Shopping for a new heating/cooling system? » « Common Causes of Furnace Fires and How to Prevent Them