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Flammable Vapor Ignition Resistant (FVIR) Water Heaters

The next gas hot water heater you buy will be a bit different than the one you have now, both in safety and, as with all "improvements", cost. That's because all tank-type gas water heaters with inputs of 75,000 BTU or less, manufactured after July 1st 2005 are being equipped with a safety device designed to prevent flashback fires. Models incorporating the new design feature are commonly referred to as Flammable Vapor Ignition Resistant (FVIR) water heaters.

According to the Consumer Product Safety Commission, a flashback fire occurs when vapors from a flammable liquid such as gasoline come in contact with an appliance's burner or pilot light and the vapors ignite. The commission estimates that there are 800 residential flashback fires a year in the United States, resulting in five deaths and 130 injuries.

How does an FVIR water heater work?

The technology prevents such fires by trapping and burning dangerous gas vapors inside the heater while preventing ignition of the vapors in the room.  The new water heaters incorporate new technology that helps accomplish the requirements of the new ANSI Standard. This technology consists of:

  • A device to prevent ignited vapors from passing out of the combustion chamber
  • A one way intake system to control the movement of makeup air into the combustion chamber
  • An inner door and burner assembly to create a sealed junction with the combustion chamber, preventing combustion air and flammable vapors from entering the chamber through the front of the water heater

While all manufacturers differ slightly in design and how to accomplish the desired outcome, they all have the same basic FVIR features in common. The Gas Appliance Manufacturers Association says the heaters are designed to keep burning vapors inside the combustion chamber until they burn out. The heaters also are designed to shut down automatically if they become clogged with dust and lint.

A flame arrestor, typically made of stainless steel, at the base of the heater prevents flammable vapors from igniting outside the heater's internal combustion chamber. The chamber is sealed so that the arrestor is the only way for combustive air to enter the unit. Should flammable vapors get through, they burn off harmlessly on the arrestor's surface.

If the heater becomes clogged with lint, dust or oil, a combustion temperature sensor will shut down the unit.

The new voluntary heater-technology standard was approved in two parts, the safety commission said. The first requirement, for flammable vapors ignition resistance, was approved in February 2000. The second requirement, for the heater to resist lint, dust and oil accumulation, was approved in November. The final standard, incorporating both parts, became effective July 1st. An industry research and development group came up with the technology to meet the requirements. Power-vented 30-, 40- and 50-gallon models will follow suit by July 1, 2004, the manufacturers' association said, and remaining models -- those with larger volumes and water heaters for manufactured homes -- will do so by July 1, 2005.

Depending on the model, the new technology will increase the price of gas-fired water heaters by up to 50 to 60%. For example, A.O. Smith, a major manufacturer of tank hot water heaters, has already introduced the technology, and it will raise the price of its basic 40-gallon model from about $410 to $485. Prices may differ among manufacturers and in different areas of the country, according to plumbers interviewed.

The water-heater standard follows another voluntary industry standard that calls for child-resistant packaging for gasoline cans, according to the safety commission. FVIR water heaters are no substitute for common sense. Never store flammable liquids or other combustible materials near any gas-fired appliance. Cleaning solvents, aerosols, paint thinner and vapor from gasoline can ignite if they come in contact with an open flame from a candle, match or pilot light.

You are not required to replace your existing gas-fired water heater with an FVIR model. But when you do need to replace it, only FVIR models will be available. Unlike with low-flow toilets, you will not be able to go to Canada to get a non-FVIR water heater. Implementation of the FVIR heaters in Canada will lag only six months behind ours. Existing models cannot be converted to FVIR.

More information is available from the appliance manufacturer, and from the Consumer Product Safety Commission at 1-800-638-2772.