Should I run the HVAC to clear the smell?

No. Running the system pulls air across contaminated duct surfaces and delivers it to every register. Switch it off, seal the filter that ran during the event in a bag as evidence, and leave it off until the system has been sampled. Portable HEPA air cleaners in the rooms people are using are the interim measure.

Can ducts be cleaned, or do they have to be replaced?

It depends on the material. Sheet-metal duct can be mechanically cleaned and treated. Flexible duct and internally lined duct have porous interiors that hold residue, and when sampling shows contamination they are usually replaced rather than cleaned. The finding is made per section from the samples, not for the system as a whole.

What about the furnace or air handler itself?

The blower housing, the coil and the cabinet interior are sampled with the ductwork. A coil that ran through a smoke event carries residue in a place that is very difficult to clean, and the protocol will say whether cleaning is adequate or the component is replaced. Combustion appliances that were in the fire area also need a mechanical inspection before they are re-fired.

How is HVAC contamination proved to the carrier?

With the same laboratory evidence as the rest of the house: surface samples from the return plenum, supply registers and duct interiors, read by microscopy for soot, char and ash; the filter that ran during the event, photographed and dated; and air sampling from registers where odor persists. The hygienist's protocol then writes the duct scope from those results.

Is duct cleaning covered by insurance after a fire?

When the sampling shows the system carried the smoke, duct cleaning or replacement is part of the remediation scope and is billed through an approved claim like the rest of the work, subject to the policy and your deductible. Without the sampling it is the item most often left out.

HVAC and Ductwork Smoke Damage: Testing and Cleaning Scope

What this service is: sampling of the HVAC system — filter, return plenum, supply registers, duct interiors and the air handler — with accredited laboratory analysis; a hygienist's protocol that specifies cleaning or replacement per duct section; certified remediation; and clearance sampling at the registers. The system is the most commonly overlooked line in a smoke claim, and the most common reason odor persists after everything else is cleaned.

How one air handler contaminates a whole house

A forced-air system moves the building's entire air volume through itself many times an hour. If it ran while smoke was present — because nobody thought to switch it off, because the thermostat called for heat, or because the fresh-air intake was open to the plume — it pulled the fine particles the EPA classifies as PM_2.5 through the filter, past the coil and the blower, and into every duct run and every room they serve. The filter caught some of it. The rest settled on duct interiors, where it stays, and every subsequent cycle scours a little of it back into the airstream. The EPA's indoor air quality guidance for smoke events centres on the system for exactly this reason: filtration and recirculation settings determine whether the HVAC protects the occupants or exposes them.

This is why a house can be cleaned room by room, pass a visual inspection, and still smell like the fire when the heat comes on in October. The reservoir is inside the walls.

What we sample in the system

The filter. The single most useful object in the house after a smoke event. Photographed in place, dated, bagged and retained; its loading is direct evidence of what passed through the system.
Return plenum and return grilles. Where the contaminated air entered the system and where deposits are heaviest.
Air handler interior. Blower housing, coil face and cabinet, sampled for the residue that settled where it is hardest to remove.
Duct interiors. Accessible runs sampled by section, because the disposition — clean or replace — is made per section and per material.
Supply registers. Wipe samples at the outlets in occupied rooms, which show what the system has been delivering.
Air at the registers. Where odor persists, sampling of the volatile fraction with the system briefly running, against background.

Laboratory microscopy identifies soot, char and ash and separates them from the dust every duct system carries. The report reads section by section, which is what allows the protocol to be specific.

Clean or replace: how the duct scope is written

A licensed industrial hygienist writes the HVAC portion of the protocol from the section results. Rigid sheet-metal duct with confirmed contamination is mechanically cleaned — agitation under negative pressure with HEPA-filtered collection — and treated. Flexible duct and duct with internal fibrous lining are porous; residue is held in the material rather than on it, and when sampling confirms contamination these sections are replaced. The air handler's coil and blower are cleaned or replaced according to what the samples showed and how accessible the components are. Registers and grilles are removed and cleaned. Work is performed by certified professionals under methods aligned with ANSI/IICRC S700, and the system is not returned to service until clearance sampling at the registers comes back at background.

If suppression water reached the system — a common outcome when the air handler sits in an attic the fire department opened — the EPA's guidance on mold and HVAC systems applies as well: a system suspected of mold contamination is not run until it has been inspected, because operating it spreads the growth through the building.

Getting the system into the claim

Duct cleaning and replacement is the item most often missing from a smoke scope, because nobody sampled the system and the adjuster's walkthrough did not include the inside of the ductwork. The laboratory results per section, the retained filter, and the hygienist's protocol are what put it in. On an approved claim the HVAC work is billed through the claim with the rest of the remediation; you remain responsible for your deductible, and coverage depends on the policy and the facts. We coordinate the documentation so that the system is scoped with the house rather than argued about after the house is finished.

When the air handler is in the attic

Attic-mounted systems sit in the most contaminated space in a fire-damaged house and, if the fire reached the roof, possibly under a deck that has been cut or charred. The system assessment and the structural inspection happen in the same space, and the roof work has to be sequenced with the duct work — there is no point installing new flexible duct under a deck that is about to be replaced. Our page on the fire-damaged roof explains how the inspections fit together; the state directory below finds the licensed roofer.

The roof is a separate inspection

Find a roofer for the inspection

A smoke test documents contamination; it does not tell you whether the deck, rafters or trusses can carry a load. Pick your state to open the National Roofing Directory's licensed-contractor listings for it, then ask the roofer for a written inspection that names each opening and each charred member.

Your state Open the state directory →

HVAC and Ductwork Smoke Damage: The System That Spread the Smoke