Why Your HVAC System Smells Bad (and How to Fix It)
Musty, burning, chemical, or rotten smells from your vents — what each one means and what to do.
Different smells point to different problems. Here's how to decode what your HVAC is telling you.
Musty / mildew — moisture in the ducts, drain pan, or evaporator coil. Needs cleaning and possibly antimicrobial treatment.
Burning / electrical — turn the system OFF immediately and call a professional. Could be a motor, wiring, or capacitor issue.
Rotten eggs — likely a dead rodent in the ducts, or a natural gas leak (call the gas company first).
Chemical / formaldehyde — could indicate a coil leak (refrigerant) or off-gassing from recent construction.
Cigarette / smoke — trapped in the ducts from prior residents. Full cleaning + antimicrobial fog usually resolves it.
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