The Safe Heating of Drywall

By David Hedman and Larry Chase

ThermaPure Building

In 1917, there were three major inventions brought to market that changed the way Americans would live in their homes forever. They were the invention of gypsum boards known as drywall, the light toggle switch that allowed you to flip one switch to turn lights off and on, and … marshmallow fluff.

While the marshmallow fluff might be delicious and the light switch is convenient, the invention of drywall changed the nature and simplicity of home and office construction, allowing for the easy partitioning of rooms and privacy for the occupants.

Most jobs in which the ThermaPureHeat method is used involve structures with drywall walls. The ThermaPureHeat method heats the ambient air inside structures up to 150 degrees for several hours in order to eliminate termites and other bugs, as well as mold, mites, allergens and other airborne pathogens. In water damage restoration, the method sanitizes the structure while it dries.

Many studies conducted during recent years show that the heating does not harm the composition of drywall, which is the basic component of so many structures. Change is hard in many industries, especially when a disruptive technology such as structural heating is used. As the ThermaPureHeat method has grown in popularity, many in the restoration industry have recycled old beliefs that high temperatures damage the gypsum in drywall. Extensive studies show that permanent temperature damage to gypsum occurs only when temperatures exceed 176°F. Temperatures fluctuating between 140°F and 176°F will experience dehydrating, but the studies indicate they will be restored to ambient levels, and the quality of the drywall will not be degraded.

The following are quotes and references from scientific studies on the relationship of ThermaPure-type temperature ranges (generally, 105°F to 150°F) and gypsum board:

  • “Calcination is a chemical and physical change in the nature of common GWB produced by heating to temperatures in excess of 80°C (176°F).” (Kennedy 2003)
  • “Gypsum board, depending on ambient air humidity, either gains or loses free water when continuously exposed to 140°F, and may be stable to occasional short exposures at much higher temperatures.” (Meyer 1982)
  • “The mass loss remains almost unchanged up to 100°C (212°F). Between 100°C (212°F) and 160°C (320°F), the mass loss of the different boards decreases between 15 percent and 17 percent as moisture is driven off. These results are reasonable as gypsum with no additives contains about 21 percent by mass of water.” (Benichou 2001)
  • “In a separate experiment, paperless wall board was exposed approximately four hours to a cool/sooty fire as a ‘ceiling’; the maximum temperature of the exposed surface was approximately 66°C (150°F). Hemp, polyurethane foam and asphalt paper were used as the fuel to produce the smoke … No dehydration of the wallboard occurred in this exposure.” (Mann 2009)

The warranties of several drywall manufacturers also bear out the evidence that the ThermaPureHeat method does not damage sheetrock. The warranty sheets warn against “continuous exposure” to high temperatures or high humidity.

The verbiage in the warranties implies some discretion. The warranties use language such as “exposed to sustained temperatures,” “for extended periods” and “prolonged exposure.” Elevated ThermaPure temperatures are typically used for only several hours and likely would not qualify as extended periods or prolonged exposure.

Some may believe that you cannot use air temperatures over 104°F to 125°F when drying gypsum. This would not only be impossible, but the impact on many industries, not just restoration, would be significant. Gypsum board will exceed both of these temperatures in many normally occurring situations. For example, here are a few instances where these temperatures are exceeded:

  • Transportation – Trailers, rail cars and pods in transit will exceed these temperatures. A 2001 study by the International Safe Transit Association measured trailer temperatures in excess of 140°F.
  • Storage – Many outdoor storage areas in the south or southwest will exceed 104°F during summer months as outdoor air temperatures exceed this regularly. Storage in facilities without air conditioning commonly exceeds these temperatures. Roof temperatures in a simulated structure in Madison, Wisconsin reached 168°F in a study by the USDA Forest Products Laboratory, resulting in a space temperature over 120°F (Winandy 1995).
  • Installation – During summer months in the southwest, drywall is installed before the air conditioning or ceiling insulation. This is normal building practice, and drywall temperatures regularly exceed 120°F in this scenario. Phoenix experienced 33 days in 2011 of outside temperatures in excess of 110°F.
  • After installation – Drywall installed in garages or other unconditioned areas will far exceed 104°F. In some areas, such as Arizona, outside temperatures will exceed 110°F for lengthy periods of time and can reach extreme temperatures over 150°F in unconditioned spaces. It is common in some southwest states not to have insulation in garage ceilings (with no livable space built over), leaving this drywall directly exposed to the high attic temperatures. Temperatures in unconditioned attics may approach 200°F during summer months in the southwest.

A number of studies validate the idea that ThermaPureHeat does not damage sheetrock. For copies of these specific studies, contact Jared Perez at 800-375-7786 or

In addition to the use of nine U.S. patents, the ThermaPure licensees receive extensive training on the safe heating of building materials. The training program uses a 300-page training manual and a test flood house for real-time experience.

This article was originally published in the February issue of C&R magazine and has been reprinted with permission from the Restoration Industry Association.