HVAC systems after water damage

In plain English

An HVAC system that gets wet can quit, run poorly, or push humid air through the whole house. If Category 2 or 3 water reaches it, it can carry that contamination into rooms the water never touched — and even a dry system, if it keeps running, can move humidity and contamination from the wet area to the rest of the building. Mold growing for other reasons can also build up inside the equipment and degrade it. Design, installation, operation and maintenance all decide whether the system controls growth or spreads it, and the S500 says owners and other interested parties should be told about conditions that put the building at risk.

The S500 says a contaminated HVAC system should not be run during water-damage restoration, and anyone servicing one has to follow the applicable laws (in Texas, HVAC work is licensed). Other things move air and change pressure in a house too — exhaust and plumbing vents, fuel-burning appliances, chimneys and fireplaces, air-exchange and energy-recovery systems, economizers, elevators, recessed lights and central vacuums — and they should be accounted for on the job.

Homes typically have up-flow, down-flow, split or horizontal systems. Down-flow and horizontal units often sit outside the living space — under the floor or in the attic — with ductwork running where no one sees it, so moisture can collect unnoticed for a long time, and wood and other organic materials nearby give mold something to feed on. Commercial systems are bigger and more varied (multi-zone, variable-volume, dual-duct and induction systems, with chillers, mixing boxes and VAV boxes) and may need a building engineer.

Before restoring the building or the HVAC, the cause of the contamination is found and the moisture source controlled; the S500 says an IEP should assess this. Sometimes the problem is the building's design or construction, putting more moisture in the house than a properly working system can handle — which raises real questions about scope and who is responsible. Restoration and remediation return a building to how it was designed; they don't redesign it or its mechanical systems.

Lined ductwork, duct board and flex duct that get wet are often better replaced than dried, and if mold has grown in them they should be removed and replaced. A full engineering evaluation of the system is outside the S500 — it points to qualified engineers or HVAC contractors — but affected systems should be inspected for cleanliness and brought back to an acceptable state, using the NADCA ACR standard for cleanliness levels and inspection methods.

HVAC cleaning or remediation usually comes after the rest of the restoration, so contaminants don't migrate into the system; if that isn't possible and the building is contaminated, the HVAC is sealed off from it. Components that could be recontaminated during drying and reconstruction are re-inspected, and cleaned if needed, after demolition and rebuilding — before containment and pressure controls come down. Temporary heating and cooling may be needed meanwhile, and any equipment used inside a containment is decontaminated or wrapped before it leaves.

Filtration slows the spread of spores from one part of a building to another. After Condition 3 mold (actual growth) or Category 3 water, the S500 says better filtration should be considered as part of preventing a repeat. Often the existing filter slot will take a better filter; if not, the system is modified to fit one — without cutting the airflow and pressure drop the system was designed for.

Once the system has been assessed and any mechanical fixes made, cleaning follows industry standards such as NADCA ACR. The minimum is a system that is visibly clean, checked by visual inspection, surface comparison or the NADCA vacuum test, and it may take more than one cleaning. HVAC equipment has plenty of hidden places for spores and growth to collect, so sampling inside the system should be done by an IEP trained in HVAC contamination. Coils are cleaned on both the upstream and downstream sides, and tightly packed coils may have to come out. A dirty coil restricts airflow and removes less moisture from the air. Because a coil can look clean and not be, the S500 recommends measuring the static pressure drop across it with a manometer or Magnehelic gauge before and after cleaning.

The bottom line: the HVAC moves the air everyone in the building breathes, during and after the work, so it belongs in the work plan. Clean (Category 1) water is drained or vacuumed out of the ducts and equipment as soon as practical and the system dried. When Category 2 or 3 water has gone directly into the system — especially internally insulated duct or fiberglass duct board — decontaminating it may not be possible or practical, and the mechanical parts are evaluated and cleaned to current industry standards.

Key points

• A wet or contaminated HVAC system can spread humidity and contamination through the whole house.
• Don't run a contaminated system during restoration.
• Attic, crawlspace and under-floor units can hide moisture for months.
• Find the cause first; an IEP assesses it.
• Wet lined duct, duct board or flex duct: often better replaced; moldy: should be replaced.
• Clean the HVAC last, to NADCA ACR; re-inspect before containment comes down.
• After heavy mold or Category 3 water, consider better filtration — without choking the airflow.
• Prove a coil is clean with a static pressure test, not just a look.

Official text

This topic is covered in our own words because the standard behind it is copyrighted; we cite it below rather than reproduce it.

Citations

• IICRC S500, ANSI/IICRC S500 Standard for Professional Water Damage Restoration — Secs. 13.1–13.2.3, the building and its HVAC system, residential and commercial systems, ductwork, pp. 72–73. Best practice
• IICRC S500, ANSI/IICRC S500 Standard for Professional Water Damage Restoration — Sec. 13.3, evaluating HVAC systems, p. 73. Best practice
• IICRC S500, ANSI/IICRC S500 Standard for Professional Water Damage Restoration — Secs. 13.3–13.4.1, filtration, HVAC assessment, cleaning and restoration, contamination considerations, p. 74. Best practice

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