Drywall dust contamination in an air handler (C) Roger Hankey Drywall Dust Contamination of HVAC

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Dust-contaminated HVAC systems:

This article describes drywall dust or construction dust contamination of air conditioning or heating system air handlers.

Minnesota home inspector Roger Hankey describes the causes and effects of dust contamination in HVAC systems that occurs particularly when the air handler is operated during construction such as as a space heater or as an air conditioner during drywall installation and taping.

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Wallboard Joint Dust and Forced Air Heating & Cooling Systems

Roger Hankey

Drywall dust contaminated air handler (C) Roger Hankey at InspectApedia.comResidential forced air heating, ventilating, and cooling systems (HVAC) are not intended to be used during construction, especially during sanding of the gypsum wallboard joints. We have inspected new houses where the system was contaminated with wallboard dust. We have also found this condition in remodeled older houses.

In the photo at page top as well as shown here we see thick drywall dust deposits inside the air handler of a new forced-warm-air furnace.

[Click to enlarge any image]

Wallboard joint dust contains fine particles and is airborne unless special joint compound and ventilation measures are used. If the HVAC system is not completely sealed during construction, dust can coat the blower, heat exchangers, cooling coil, and ducts, since most furnace filters (if present) either don’t capture the fine particles, or collapse from excessive dust.

Wallboard dust is an eye and lung irritant. Material safety data sheets caution workers to protect their eyes and lungs against exposure to the dust. HVAC equipment manufacturers warn dust can adversely affect their equipment, including reducing efficiency and life span. Cleaning wallboard dust from HVAC equipment is difficult, costly, and cannot restore equipment to new condition.

Also, HVAC equipment manufacturers warn against using the system during construction as equipment may be subjected to abnormal operating conditions. Continuous furnace operation to cure wallboard joint compound can heat stress equipment. Also, if the filter is clogged, air flow for proper heat transfer will be limited. This causes the high temperature limit switch to cycle equipment on and off, placing abnormal stress on the heat exchanger. Further, dust can damage blower motor bearings.

Canadian gas heating equipment manufacturers have put Canadian home builders on notice that as of May 2017 their installation instructions will prohibit use of their equipment as construction heaters.

Canadian manufacturers explain their decision on pages 2-3 of a document at:

US manufacturers have not banned use of their equipment during construction, but most US installation instructions are similar to the following: (author’s highlights)

Use of Furnace as Construction Heater

Lennox does not recommend the use of SL280UHV units as a construction heater during any phase of construction.

Very low return air temperatures, harmful vapors and operation of the unit with clogged or misplaced filters will damage the unit.

SL280UHV units may be used for heating of buildings or structures under construction, if the following conditions are met:

The vent system must be permanently installed per these installation instructions.

A room thermostat must control the furnace. The use of fixed jumpers that will provide continuous heating is not allowed.

The return air duct must be provided and sealed to the furnace. Return air temperature range between 60°F (16°C) and 80°F (27°C) must be maintained.

Air filters must be installed in the system and must be maintained during construction.

Air filters must be replaced upon construction completion.

The input rate and temperature rise must be set per the furnace rating plate.

One hundred percent (100%) outdoor air must be provided for combustion air requirements during construction. Temporary ducting may supply outdoor air to the furnace. Do not connect duct directly to the furnace. Size the temporary duct following these instructions in section for Combustion, Dilution and Ventilation Air in a confined space with air from outside.

The furnace heat exchanger, components, duct system, air filters and evaporator coils must be thoroughly cleaned following final construction cleanup.

All furnace operating conditions (including ignition, input rate, temperature rise, and venting) must be verified according to these installation instructions.” - source cited at REFERENCES

Drywall dust in metal ductwork (C) Roger Hankey at

Above: drywall dust is also visible inside the metal ductwork of the system shown here.

Installations of new or replacement furnaces are required to be permitted and inspected in Minnesota jurisdictions that enforce the State Mechanical Code.

The authority for requiring the system to be clean comes from the Minnesota State Mechanical code which reads as follows:

1346.0103 MAINTENANCE.
Mechanical systems, both existing and new, and parts of those systems, shall be maintained in proper operating condition in accordance with the original design and in a safe and sanitary condition. Devices or safeguards which are required by this code shall be maintained in compliance with the code edition under which they were installed.

The owner or the owner's designated agent shall be responsible for maintenance of mechanical systems. To determine compliance with this provision, the building official shall have the authority to require a mechanical system to be re-inspected.

The 2012 International Mechanical Code section 304 Installation, states:

304.1 General
“Equipment and appliances shall be installed as required by the terms of their approval, in accordance with the conditions of the listing, the manufacturer's installation instructions and this code. Manufacturer's installation instructions shall be available on the job site at the time of inspection.”

Recommendation for new house purchasers:

1. If the purchase contract is to be signed PRIOR to construction, have a qualified attorney review the contract and include language to state that the purchaser is entitled to a HVAC system that was NOT used during construction and is free of construction dust and debris. Similar legal review is recommended prior to signing a purchase agreement for a recently completed new home including steps 2 & 3 below.

2. Have a qualified independent inspector or HVAC contractor examine the system prior to the closing to determine if the system was in use during construction and if it is free of dust and debris.

3. If the system has dust and debris, or has other signs of use during construction, have the attorney take steps to enforce contract provisions to replace all contaminated and/or used system components.

Buyers and inspectors are advised to obtain the furnace installation manual. Read the section on use during construction and the limitations section of the warranty. These provisions will be your support for objecting to any dust found in the furnace.

The same approach is recommended for purchasers of remodeled existing houses, or “flipped”, if the HVAC system is coated with drywall dust.

Similar agreements and provisions are recommended for home owners working with remodeling contractors to protect the HVAC system prior to remodeling or additions.

©2017 & (used with permission) All rights reserved.

Generalizing: dust contamination of HVAC systems

Dirty air filter (C) Daniel FriedmanDrywall-dust contamination inside of an air handler in new construction is a specific case of a more general problem with sources of contamination in HVAC systems, air handlers, ductwork and related components.

For example operating air handlers for either heating or cooling during a mold remediation project (or before a mold remediation project if the situation is bad) can produce other contamination and health hazards, and depending on the type of ductwork the cleaning or repair cost in both cases can be quite high.

Roger Hankey is principal of Hankey and Brown home inspectors, Eden Prairie, MN. Mr. Hankey is a past chairman of the ASHI Standards Committee. Mr. Hankey has served in other ASHI professional and leadership roles. Contact Roger Hankey at: 952 829-0044 - Mr. Hankey is a frequent contributor to


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