Bang. Bang. That's a noise that homeowners don't expect to come from the ductwork or furnace. When it happens, it can be startling and worrisome. Is something wrong with the furnace? Is something loose in the ducts? There may be no issue to worry about, however, in some cases, this unexpected furnace noise and duct noise can be a sign of trouble.
Causes of Banging or Popping in Ductwork
Many residential ducts are rectangular in shape and made from metal. When the heating or cooling system comes on, there's an expected buildup in pressure within the ducts. The expanding pressure can cause the long sides of the rectangle to expand as the air is flowing. This can cause an initial popping or banging noise.
Once the air stops flowing, the pressure goes down. As the long sides of the rectangle contract with the reduction in pressure, the metal ductwork can react with a second popping or banging sound.
This kind of banging sound isn't a sign of trouble in most cases. It's just a sign that the ductwork is expanding and contracting with pressure changes.
Newer systems that have a layer of rigid insulation on the outside may not have this issue. An older system may not make this sound due to a buildup of dust on the inside of the ductwork. With older systems, it most often shows up after a good duct cleaning removes the sound insulation from the inside of the ducts. All of a sudden there's a banging sound that was never there before.
When Banging Ducts Signal Trouble
Now, there are a few cases when that duct noise is a sign of trouble. If you also hear a whistling sound, you may have a problem. This may be a sign that your duct covers aren't properly sized. Have a heating professional inspect the covers and make sure they're sized correctly. If they're not, replace them and the whistling should stop.
In some cases, however, the whistling may just be a sign the system is working at peak efficiency. It's a situation best judged by a trained heating professional.
Can Banging Be a Sign of Something Else?
If your furnace is fueled by oil or gas, a delayed ignition within the furnace may be causing unexpected furnace noise. Inside the furnace are a series of burners that ignite the oil or gas and generate heat. Older burners can rust or get clogged by debris. When the thermostat signals for heat, the burner's valves turn on and start emitting fuel.
In a healthy system, ignition would be instantaneous. With a clogged burner, however, ignition can be delayed. The fuel has to build up to a certain level before ignition happens. Once it happens, the built-up fuel will ignite with a sudden bang.
This kind of ignition isn't normal. It can be dangerous for anyone standing close. It can cause a fire if the fuel happened to escape the ignition chamber. Over time, this kind of ignition sequence can cause damage to the system's heat exchanger. If you suspect that the burners are clogged, you need to fix the situation as soon as possible.
The solution to this problem is to have a professional come out to inspect and clean the burners. If you have an annual inspection of your home's heating and cooling system, make sure the technician inspects the burners as part of the service.
If you have any furnace noise or duct noise that you can't identify, call in the heating and cooling professionals at Thermacon Service Company. We provide air conditioning, heating and refrigeration services in Beaumont, Orange, and Port Arthur, Texas, as well as surrounding areas.
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