If you have just started using your heating system and you notice loud, banging noises when the system turns on and off, don't be alarmed. While you may need a thorough cleaning of your ductwork and air filters, the cause of your loud noises is likely nothing more than the expansion and contraction of the ductwork as the air within heats and cools rapidly. Improving the air flow in your ductwork should help lessen the amount of bangs that you hear, which is done in a variety of ways. If you aren't familiar with your heating system, it's time to call a professional HVAC contractor to service your heating system for the season.

Your Fan Isn't Working Properly

There is a fan in your heating system that blows air through your ductwork and up into your home to warm it. If the fan is dirty and clogged or it is no longer working, you will hear loud noises when the system turns on and off. A malfunctioning fan will need to be replaced. You can try cleaning out a dirty fan using a vacuum cleaner to see if that helps solve the problem; otherwise, call for help if the noises continue.

Try Opening Air Vents

Ductwork also contains a number of air vents throughout the system. When the air can't flow freely through your ductwork, you will get the loud banging noises from expansion and contraction of the metal. Air vents can be opened to help improve the air flow within the ductwork, so try opening one at a time to see if that fixes the problem. While you should still have your ductwork cleaned and your system serviced, you can probably decrease the volume of the banging by opening up some air vents.

Look for Air Leaks

Sometimes a piece of ductwork will become loose, and this causes problems with the air flow. You can try walking along your ductwork feeling for a leak or try using a stick of incense to see if the smoke blows away from any areas of ductwork. Check the creases, and if the smoke blows away quickly, you know you have an air leak.

There Could be Critters

Small animals can get into your ductwork, making a little nest of all kinds of materials. This is another reason that airflow in your ductwork can be disturbed, causing the ductwork to bang and clang when it is turned off and on.