Strange Smell from HVAC
Quick Answer
Strange HVAC smells usually indicate specific problems. Musty = mold, burning = electrical/dust, rotten eggs = GAS LEAK (leave immediately!), chemical = refrigerant leak. Most can be addressed, but gas and burning smells require immediate action.
Safe Checks You Can Do
- 1Replace air filter - Dirty filters can harbor odor-causing bacteria and mold.
- 2Check condensate drain - A clogged drain creates stagnant water that breeds mold.
- 3Inspect accessible ducts - Look for visible mold, debris, or pest evidence.
- 4Check floor vents - Remove and look for debris, dead pests, or mold.
Smell Types & Causes
- Rotten eggs / sulfur
GAS LEAK! Leave immediately. Do not use light switches. Call gas company from outside.
- Burning / electrical
Could be dust at startup (normal) or overheating motor/wiring (dangerous). If persistent, shut off.
- Musty / moldy
Mold in ducts, on coils, or in condensate system. Replace filter and clean drain.
- Chemical / sweet
Refrigerant leak. Can be harmful. Open windows and call for service.
- Sewage
Dry P-trap, backed-up sewer line, or dead animal in ductwork.
When to Call a Pro
- Rotten egg smell - LEAVE IMMEDIATELY and call gas company
- Persistent burning or electrical smell
- Chemical or sweet smell indicating refrigerant
- Musty smell that doesn't improve with filter change
- Sewage smell that persists
Related Symptoms