Why Are My Air Ducts Popping? Normal Pings vs Sounds to Fix

Which popping sound do you have?

Expansion pings: normal

Sheet metal ducts are galvanized steel or aluminum (Trane). When the furnace sends warm air through ducts that have cooled off, the metal reacts to the fast temperature change. CenterPoint Energy describes this pinging or tapping as normal thermal expansion in a healthy system. You'll usually hear it as warm air starts flowing and again as the ducts cool after the heat shuts off.

Why it's louder in winter

CenterPoint Energy says that in cold places furnaces run more often and work harder, so you hear more pinging and popping as the ducts expand and contract (CenterPoint Energy).

Oil-canning bangs: check airflow first

The louder bang comes from air pressure, not heat. CenterPoint Energy calls this popping oil-canning and says it happens when the air pressure in the ducts changes quickly as the blower stops. The name comes from the way thin sheet metal snaps in and out, like the side of an oil can. CenterPoint also says that if the sound is very loud, the ducts may be too small or the filter may be clogged, and that a dirty filter can make ducts pop loudly because the system has to work harder to pull air in.

Start with the filter; our guide How to Tell If Your Furnace Filter Needs Changing walks through the light test. If you hear a similar bang when the blower starts, the same airflow checks are a sensible first step. Then work through the rest:

1. Replace the filter if it's dirty. Check the filter about every 30 days during heating season and replace it when it looks dirty, as CenterPoint recommends (CenterPoint Energy).

2. Open supply registers. Carrier notes that closing too many supply registers disrupts the airflow the system was balanced for (Carrier).

3. Clear return grilles of furniture, rugs and drapes.

4. Listen for where it's coming from. Note whether it's a trunk duct near the furnace or a branch run, and whether it happens at blower start, blower stop or both. That helps a technician find the panel.

If the bang continues with a clean filter and open vents, a technician can measure airflow and static pressure and check whether the ducts are undersized. Trane recommends calling a pro when vents rattle or whistle, since it can mean a duct sized incorrectly or too much airflow (Trane).

Some supply ducts also have dampers, small adjustable plates that control airflow to parts of the house (Trane). Closed dampers change duct pressure the same way closed registers do, so a technician can check them.

What you can do yourself, and what needs a pro

You can do the filter, register and return checks above. ENERGY STAR says some homeowners also seal accessible ducts themselves, using mastic sealant or metal tape and never duct tape, and insulate ducts in attics, crawlspaces, unfinished basements and garages (ENERGY STAR). Sealing and insulating won't stop oil-canning by itself, but leaky ducts are worth fixing while you are looking: ENERGY STAR estimates that in a typical house about 20 to 30 percent of the air moving through the ducts is lost to leaks, holes and poor connections.

Leave it to a pro if the bang persists with a clean filter and open vents, if the ducts may be undersized, or if a panel needs to be stiffened or a section replaced. ENERGY STAR notes that most heating and cooling contractors also repair ductwork.

When the noise isn't the ducts

A boom or bang from the furnace cabinet when the burners light is not duct noise. CenterPoint Energy lists a loud boom or bang at startup among furnace noises that may signal a problem. Trane says banging sounds alongside short cycling, soot or a metallic smell are reasons to call for furnace repair and to shut the furnace off in the meantime (Trane). Don't keep restarting a furnace that booms.

If you smell rotten eggs, leave the house and call your gas company from outside, as Trane advises.