If your furnace seems to protest loudly every time you turn it on, you aren't alone. Many homeowners have experienced mysterious banging or booming noises when their furnace starts up, but the causes of this phenomenon are not as widely understood. This guide will explain the two most common causes of a banging noise when you turn on your furnace and how they may indicate that you need residential heating system repair.
Cause 1: Expansion in Your Ductwork
You may be surprised to learn that your ducts move slightly when you use your furnace or air conditioner. Residential air ducts are typically made of galvanized steel or aluminum. These metals are favored because they are long-lasting and durable, but they are also excellent conductors of heat. Like other conductive materials, metal air ducts will expand when they heat up and contract when they cool down.
In addition to temperature changes, ducts will move and expand slightly in response to air pressure from your HVAC system. Air pushes on the inside walls of your ducts continuously while you use your furnace or air conditioner. The pressure will be even higher in places where your ducts bend around corners and in places where clogs have formed thanks to dust and dirt buildup.
Duct expansion that is caused by temperature and air pressure can create the booming sound you hear when you start your furnace. If there are any small dents or creases in your ducts, these forces can be enough to "pop" the bent metal back into place, much like removing a dent from a car.
The sound of your air ducts expanding and popping reverberates through the ducts as a loud booming noise. While duct popping is not harmful, it can certainly be annoying. A professional duct inspection can locate problem areas in your ducts, and HVAC technicians can straighten, replace, or brace your ducts when needed to prevent loud noises caused by duct expansion.
Cause 2: Delayed Ignition due to Dirty Furnace Burners
The second possible cause of a booming noise when you turn on your furnace is more serious than noisy ducts. Your furnace burner can become coated with dirt, soot, and other grime and combustion byproducts as you use your furnace. A dirty burner can increase the amount of time it takes for your furnace to ignite and allow gas to build up inside the combustion chamber. When the burner finally ignites, all this built-up gas combusts at once and creates a small explosion inside your furnace!
Delayed ignition is a problem that must be dealt with promptly because the intense combustion can cause damage to your furnace. In the worst case, the explosive effect of delayed ignition could crack your furnace heat exchanger and cause a gas leak.
If you're having problems with booming sounds from your furnace, don't hesitate to schedule a professional HVAC service. An HVAC technician can get to the root of the problem and ensure that your furnace is safe to operate.