Your HVAC After a Houston Flood: What Can Be Cleaned, What Has to Go

Everybody in this city knows the drill for drywall: cut it four feet up, haul it out, dry the studs. Far fewer people know what to do with the HVAC system, and it is the part that quietly determines whether the house smells right a year later.

We have put cameras into a lot of post-flood ductwork in Houston. Here is what the footage teaches, sorted into what we can genuinely clean and what an honest company tells you to replace.

First, the thing nobody wants to hear

Flood water is not water. Even a foot of street water in a Houston neighborhood carries sewage, fuel, lawn chemicals, and whatever came out of the bayou. Category 3 contamination, in the restoration industry's language. Once it has been inside a porous material, cleaning does not restore it — it just makes it look better.

That distinction drives every decision below.

What has to be replaced

Flex duct that was submerged. Flex is a plastic inner liner over a wire helix wrapped in fiberglass insulation inside an outer jacket. Water gets between the layers and stays there. There is no cleaning method that reaches inside that assembly. Submerged flex comes out. Every foot of it.

Duct board, wet, anywhere. Duct board is compressed fiberglass with a foil facing, and it is everywhere in Houston homes built from the seventies through the nineties. It absorbs water like a sponge, holds it, and grows mold from the inside out. Wet duct board is a demolition item, not a cleaning item.

Insulation and the interior lining of the air handler. The lining inside the cabinet is porous. If water reached it, it goes.

Anything that stayed wet more than about 48 hours, regardless of material. That is the general threshold at which microbial growth is established rather than possible.

Electrical and gas components that were submerged. Furnace burners, control boards, blower motors, contactors, capacitors. This is a licensed HVAC contractor's call, not a duct cleaner's, and it is a safety call — a submerged gas furnace should be evaluated before it is ever fired.

What can genuinely be cleaned and kept

Bare sheet metal trunk lines. Galvanized duct is non-porous. If a metal trunk took water and the insulation on it can be removed and replaced, the metal itself can be cleaned, sanitized with an appropriate product, and returned to service. In many Houston homes the metal trunk survives while everything branching off it does not.

Registers, grilles, and boots. Metal, non-porous, cleanable.

The evaporator coil and drain pan, usually. If water did not reach the air handler, these need the same attention as always. If it did, the coil often cleans up but the cabinet lining under it does not.

Any duct in the attic that stayed dry. This is the good news in most single-story Houston floods: attic ductwork frequently never got wet at all. The problem there is different — the system ran during or after the event and pulled contaminated, humid air through clean ducts. That is a cleaning job, not a replacement job.

The mistake that costs the most: running the system too early

The most damaging thing we see is a homeowner turning the AC back on to help dry the house out.

If the return, the plenum, or any duct took water, running the blower distributes contaminated material through every clean part of the system and every room in the house. A localized problem in one wet duct becomes a whole-house problem in about an hour.

Leave the system off at the breaker until someone has inspected it. Dry the house with rented air movers and dehumidifiers, which is what restoration crews use anyway. Then, once the system has been cleared or repaired, run it — Houston humidity after a flood is the other half of the problem, and a house that sits closed and damp for two weeks in August grows things independent of the flood water.

Documentation, because there is an insurance claim

This is where the camera work earns its keep. What we produce on a post-flood inspection, and what you should insist on from anyone:

1. Dated camera stills or video from inside the ducts, with the location of each shot recorded.
2. A high-water mark record relative to each component — the air handler base, the return plenum, the lowest duct run.
3. A written scope separating replace from clean, with the reason for each.
4. Post-work imagery from the same access points.

Adjusters approve what is documented and argue about what is described. A folder of labeled before-and-after footage is worth more than any amount of explaining. Keep your own copy; do not rely on the contractor to retain it.

While you are putting the house back together

One item outside our trade that we mention on almost every post-flood job, because homeowners consistently forget it: think about who has had keys to your house. After a flood, that list usually includes a restoration crew, a mitigation subcontractor, a plumber, an electrician, a flooring crew, and possibly an adjuster — plus whatever keys were left in a hide-a-key or floated out of a kitchen drawer. Rekeying is a ten-minute-per-door job and it is the cheapest closure you will buy that month. HTX Locks has a solid rundown of when to rekey versus replace after a flood or a break-in that covers what water does to lock hardware too.

Also worth doing while walls are open: have your ducts sealed properly before the drywall goes back. Access will never be this good again.

When you are ready

We inspect and clean across the metro Monday through Saturday — Houston, Katy, Cypress, Spring, Humble, Kingwood, Atascocita, Friendswood, League City and more.

The first thing we do is put a camera in the system and show you the footage, so the replace-versus-clean decision is one you make looking at the same evidence we are. If it turns out to be growth rather than debris, that is a different scope — see air duct mold removal and our piece on when duct mold is real and when it is a sales script. Otherwise, air duct cleaning is where most post-flood homes land.