Air Duct Sanitizing in San Mateo, CA

Does sanitizing a duct actually fix the smell?

Usually not by itself. Sanitizer kills what it touches. It does not remove the moisture that fed the growth. In San Mateo that moisture is almost always the crawlspace. Flex that sagged off its hangers pools in the belly. Uninsulated metal runs sweat in damp crawlspaces. Growth shows on duct exteriors and at boot connections. Spray the inside and the outside problem continues.

So the order matters. Clean first, mechanically. Supply and return, blower wheel, coil surfaces, registers and boots. Sanitizing goes last, on cleaned metal, and only where growth was actually found. Fogging a dusty duct just glues dust down.

Panned floor-joist and wall-stud returns are the hard case. Older Peninsula homes used the cavity itself as ductwork. Those were never sealed. They pull crawlspace and wall-void air straight to the blower. You cannot sanitize a wall cavity in any lasting way. Sealing and lining is the real answer there.

Ask what product is used and whether it is EPA-registered for HVAC surfaces. Ask to see photos before and after. If the duct jacket is torn from rodents under a raised foundation, sanitizing is the wrong purchase. Replace that run instead.