Gas fired water heaters were required for many years to be elevated a minimum of 18-inches above the floor when installed in a garage, because of the possibility of the flame at the base of the water heater igniting gasoline vapors from a car parked in the garage or any of the other flammables that are commonly stored there. Gasoline vapor is heavier than air and tends to collect near the floor, so the requirement made sense. But there were still thousands of house fires attributed to water heaters each year.

    As a result, design changes were mandated by the Consumer Products Safety Commission (CPSC) and all 30, 40, and 50 gallon gas-fired water heaters manufactured after July 1, 2003 have been required to have Flammable Vapor Ignition Resistant (FVIR) technology. It’s also worth noting that a group of manufacturers helped develop the standards and began voluntary implementation of the technology before it was required.

     FVIR water heaters are specifically designed to prevent “flashback” vapor ignition fires in three ways:

1. Only one-way flow of air into the combustion chamber.
2. A flame arrestor plate to prevent any ignited vapor from passing out of the combustion chamber.
3. A sealed burner compartment door assembly.

    The American National Standards Institute (ANSI) established standard ANSI 21.10.1a-2002, effective July 1, 2005, that further defines the requirements and applies to all water heaters of 75,000 BTU or less.  Because FVIR water heaters have a closed combustion chamber, you can no longer open a panel at the base and reach in with a match to light the pilot.

    If any flammable vapors do manage to get into the combustion compartment, they are ignited in the sealed chamber, and the flame arrestor plate keeps any flames from escaping. Each manufacturer has their own slightly different design for FVIR safety, and they now have incorporated features that shut of the flow of gas and seal off the combustion air if a flammable vapor event occurs.

    Also, see our blog posts When is a water heater drain pan required? and Why is my water heater making strange (rumbling, gurgling, knocking or banging) noises?

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Here’s links to a collection of more blog posts about WATER HEATERS:

• Are water heaters required to be raised off the floor? 

• Can a Temperature and Pressure Relief (TPR or T&P) valve be mounted to discharge horizontally?

• Where are gas water heaters not allowed to be installed?  

• Is the minimum size water heater inlet pipe 1/2" or 3/4" according to the building code? 

• Can you use a light switch for a water heater disconnect? 

• Why is an older water heater an insurance problem?

• How can I tell if a water heater is HUD-approved for mobile/manufactured homes?

• Can the temperature and pressure relief (TPR) valve discharge pipe for a mobile/manufactured home water heater terminate under the home? 

• What is the purpose of a thermostatic mixing valve above a water heater? 

• Does a tankless gas water heater still work with no electricity during a power outage?  

•  Why do water heaters have a sacrificial anode? 

• What is the difference between a manufactured/mobile home water heater and a regular water heater? 

• Does a tankless water heater require a pressure relief valve? 

• Why is there water in my water heater drain pan?

• What does it mean when a water heater Temperature/Pressure Relief (TPR) discharge pipe is "trapped"? 

• Can I leave a gas water heater in place when remodeling a garage into a family room or bedroom? 

• Where do I find the water heater in a mobile home?

• Does a tankless water heater in an attic require a drain pan? 

• Does an electric water heater require a disconnect? 

• Is a catch pan and drain piping required for a replacement water heater?

 • What is the difference between a single element and dual element electric water heater? 

• What is a heat pump water heater?

• What is a dielectric union?

• What's that powdery crust on the pipe connections at the water heater? 

• What does it mean when a gas appliance (water heater, furnace, or range) has been "red tagged"?

 • What is the difference between a regular water heater and a direct vent water heater? 

• What is the difference berween a regular water heater and a power vent water heater? 

• What is backdrafting at a gas water heater? 

• How do I determine if a water heater is gas or electric?  

• What's the valve with the flip-up handle on the water heater for?

     Visit our WATER HEATERS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.