Why is my furnace making a banging noise?
A bang when the furnace starts is usually delayed ignition — gas builds up before lighting — or expanding ductwork. Delayed ignition deserves a technician soon: it stresses the heat exchanger. A bang when the blower stops is almost always duct metal flexing, which is annoying but harmless.
Likely causes
- Delayed ignition — Dirty burners light late; the small explosion of accumulated gas makes the boom.
- Duct expansion ('oil canning') — Thin duct metal pops as pressure changes — noise only, no danger.
- Failing blower motor or belt — Rumbling or squealing that changes with fan speed points here.
What you can check yourself
- Note when it bangs: at ignition, during the run, or at shutdown — that timing is the diagnosis.
- Replace the filter; restricted airflow makes several noises worse.
- Smell gas or see soot around the unit? Skip DIY entirely (see below).
Typical cost
Typical repairs in Richmond, VA: burner cleaning/ignition service $150–$400; blower motor $400–$800; heat exchanger issues usually mean replacement ($5,500–$10,000 installed).
When to call a pro
Gas smell, soot, a carbon monoxide alarm, or a bang at every ignition cycle — call now. Heat exchanger cracks are the serious end of this symptom.
HVAC pros in Richmond, VA
- Hungerford Heating & Cooling · 1604 E Broad St, Richmond, VA · 18046484703
- Armstrong Mechanical Services Inc · 1011 E Main St Ste 214, Richmond, VA · 8045412622
- Kelleher Hvac · 1301 School St, Richmond, VA · 18046497501
- Tuckahoe Heating and Cooling LLC · 1129 Gaskins Rd #202, Henrico, VA · +15402933975
- Booker Heating And Air Conditioning, LLC · 1723 Byron St, RICHMOND, VA · 8046525971
- Commonwealth Heating And Contractors Inc · 3200 Milburn Ave, Richmond, VA · +18042221365
- Samson Insulation · 1321 Maxie Ln, Richmond, VA · (804) 373-7196
- 1st Due Solutions, LLC · 4248 Oakley Ct Ste H, Richmond, VA · 8048522279
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Data by Servik — verified local pros from official license records and public sources. Cost figures are typical ranges, not quotes; a pro's written estimate is the real number.