Wondering Why Your Home’s Air Ducts Are Making Such a Clatter?

One common aspect of residential living is that every house, no matter how big or small, old or new, has its own peculiar noises. The more fanciful among us might attribute these sounds to ghosts – hopefully friendly ones – banging around in walls and attics. However, it’s much more likely that the author of these disturbing noises are the ducts that supply and remove conditioned air to and from rooms in your home.

Before exploring why your ducts are producing odd noises, here’s a short explanation of ductwork: Forced-air heating and cooling systems, the most common type of HVAC system in residential settings, rely on equipment – furnace, heat pump or AC – to create warm or cool air. Once that air has been conditioned, it must be circulated throughout your home and delivered directly to rooms.

That’s where ducts enter the picture. A powerful fan that’s part of your heating and cooling equipment blows the conditioned air through a network of large pipes (aka ducts) to individual rooms, where the air emerges through registers. Most rooms also contain return registers where spent air is sucked in and returned via ducts to the HVAC equipment. Every ductwork system has both supply and return ducts to complete the circuit.

What Causes Noisy Ducts?

The most common source of the banging, rattling and thumping in ductwork is the expansion of duct sections as conditioned air moves through them at sufficient pressure to force expansion of the duct walls.

This is especially common after a periodic duct cleaning. After dust and debris that’s accumulated in ducts over a several-year period has been removed, air flows through ductwork at greater pressure. As a result of this, the duct walls are more prone to expansion, often producing a popping noise.

The shape of ductwork also may influence the amount and type of noise that is produced. Rounded ducts tend to accommodate increases in interior air pressure better than square duct sections, while rectangular ducts are the most vulnerable to expansion and the resulting noise.

The good news is that most often the popping noise produced by duct expansion is totally safe. It signals that your forced-air heating and cooling system is doing its job. In the same way, if you hear a whistling sound coming from vents when the furnace or A/C is operating, this just means your system is delivering conditioned air the way it’s been designed to do.

Some HVAC Noises Are Not Welcome

However, if you hear a loud popping noise, or even a small boom, being emitted by your furnace, this could be a more serious issue. It might signal that the furnace burners are blocked by debris and/or are rusting out, which delays ignition of the natural gas, propane or heating oil. After a brief passage of time, as the fuel accumulates, it will ignite with a small explosion. This is an issue that you’ll want your dependable Cincinnati HVAC contractor to look at, since it can damage your furnace and even create a safety hazard.

Similarly, troubling noises coming from the furnace blower can be the symptom of more serious issues. Your equipment is basically trying to warn you of problems that should be addressed.