After a fire, smoke residue enters the HVAC system. Metal ducts can often be cleaned and ‘encapsulated’ with a sealant to lock down microscopic particulates. However, flexible ducts (flex) and fiberglass duct board (plenums) are porous and cannot be effectively cleaned or sealed. The IICRC and NADCA recommend replacement of all porous HVAC components to prevent recurring odors and health risks.
“You can paint over soot on metal, but you can’t paint a sponge. If your ducts are fiberglass, the smoke is inside the material. It has to go.”
— HVAC Restoration Specialist
Encapsulation is a restoration process used primarily on non-porous surfaces like galvanized steel. Once the soot is physically removed through agitation and HEPA vacuuming, a specialized chemical sealant (often called “soot lock”) is sprayed throughout the interior. This coating traps any remaining microscopic odors and prevents them from off-gassing into your living space.
| Duct Type | Material | Smoke Remediation |
|---|---|---|
| Rigid Metal | Galvanized Steel | Clean & Encapsulate |
| Flex Duct | Plastic/Fiberglass | Replace |
| Duct Board | Fiberglass | Replace |
The plenum is the distribution box connected directly to your furnace or AC air handler. In many modern homes, this is constructed from fiberglass duct board. Because fiberglass is essentially a web of glass fibers, it acts as a filter for smoke particles. Unlike metal, you cannot “scrub” the inside of a duct board plenum without destroying the material integrity, and sealants cannot penetrate deep enough to neutralize the trapped odors. When smoke enters a fiberglass plenum, replacement is the only industry-standard solution.
No. The ridges and porous insulation trap soot permanently. Flex ducts should always be replaced after a fire.
Related Reading: Why Fiberglass Duct Board Cannot Be Cleaned
Next Steps: Schedule HVAC Smoke Inspect
