This one needs a licensed pro
Have it checked: a musty smell at the registers
A musty smell with a clean filter can mean mold or mildew in the ductwork or the coil. An HVAC technician can find out.
Why this happens
Trane says a musty smell from the registers can mean mold and mildew in the ductwork or the air filter, and that the problem will come back until the excess humidity behind it is dealt with. Carrier says a musty or moldy smell can point to mold or mildew in the ductwork or the furnace-mounted evaporator coil, and Lennox says bacteria can build up in places that are hard to clean.
What to do right now
- Call an HVAC company and say the smell is musty and that the filter is clean. Trane says they may offer duct cleaning or can recommend someone.
- Don't open the furnace or the cooling coil area, and don't try to clean inside the ducts yourself.
- Ask the technician about humidity in the house, since Trane says the smell can come back otherwise.
- If the smell changes to gas or rotten eggs, or you see smoke, leave the house now without touching any switch or the thermostat, and call 911 or your gas utility from outside. If it changes to a plastic or electrical smell, set the thermostat to Off and call an HVAC technician.
When to stop. If you smell gas or rotten eggs, leave the house and call 911 or your gas utility from outside. If a CO alarm sounds, or anyone has a headache, dizziness, weakness or nausea, get outside to fresh air and call 911.
What to tell the HVAC technician
- That the smell is musty, and when it started.
- That the filter is clean and when it was last changed.
- Whether the smell is strongest when the air conditioner runs, if you have central cooling.
- Whether the house feels humid or you see damp spots.
Build the full list: what to tell the HVAC technician.
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