A few times a month, I run across gas water heaters that has been installed either on the floor, or a few inches off the floor. Mechanical codes state that for fuel burring units such as gas and oil, the combustion chamber and ignition source should be a minimum of 18 inches above the floor. This requirement is intended to minimize the possible ignition of flammable vapors that may accumulate in the area of the unit.

The potential for this hazardous condition can occur with the dispensing or accidental spillage of gasoline, paint thinners or other combustible products commonly used in the home. Flammable liquids can quickly vaporize, and being heavier than air, remain near the floor and are subject to instantaneous ignition from a  spark or open flame like a pilot light.

This type situation has resulted in numerous injuries and deaths over the years as the ignited vapor flashed, covering anyone or anything within its path. This can happen in any enclosed area, but is more common in garages where gasoline and other flammable liquids are stored.

Studies have shown that above a point of 18", the specific density of vapors that result from accidental spills is not at a readily ignitable level. Positioning the source of open combustion above this level lowers the risk of a flashover - or can give anyone additional time to vacate the area before vapors are ignited.

This height requirement has been in effect for most municipalities since the 1970's when the code was first introduced. Some municipalities are now requiring electric water heaters to be mounted at this height as the lower element is below the 18" level, and the thermostat contacts are considered an ignition source.

This posting and the continents written here are the intellectual property of Michael Thornton of Complete Home Inspections, Inc. providing Nashville home inspections for Brentwood and the Davidson and Williamson Counties of Middle Tennessee. The views and opinions expressed are just that - views and opinions of Michael Thornton and those who comment.  This post is part of the ActiveRain Real Estate Network, which is a social network highlighting the best of Web 2.0.  Information and is provided with the intent of educating and assisting home owners, home sellers, home buyers and real estate investors with information the can be used to make better real estate decisions. 

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