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Flammable Vapor Ignition Resistant (FVIR) Water Heater

August 9th, 2009

In 2003, a new standard for water heaters was developed and phased in.  It says, “The water heater should not ignite flammable vapors outside the water heater created by the spilling of gasoline onto the floor.”  The Consumer Products and Safety Commission found thousands of fires, injuries and deaths were related to water heaters.  Most of these cases were because of improper storage or handling/spillage of gasoline.

If the tank is in compliance with the FVIR standards, it does not have to be raised 18 inches in garages or similar locations, unless required by the manufacturer or local code authorities.

A FVIR water heater has the following components: 1) a device to prevent ignited vapors from passing out of the combustion chamber, 2) a one-way intake system to control the movement of makeup air into the combustion chamber, 3) 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.

All FVIR water heater tanks have things in common.  1) A flame arrestor plate.  Located under the burner, the metal plate is designed to allow combustion air into the combustion chamber but keep flames from escaping downward and igniting flammable vapors below.   2) Thermal cutoff switch.  It is designed to shut down the heater if it senses excessive temperatures caused by inadequate combustion air inside the chamber.  Inadequate combustion air can be caused by an explosion of flammable vapors, inadequate venting, inadequate makeup air or the accumulation of lint, dust, or oil on the screen.  3) A lint, dust, and oil screen.  The screen is designed to protect the combustion process from lint, dust, or oil.  The screen openings can become clogged, especially when the tank is located in a basement or utility room.

FVIR System on a Bradford White Defender Water Tank
During normal operation, air for combustion is drawn into the water heater through the openings in the jacket.  This air travels down and around the combustion chamber and enters through holes in the very bottom of the corrosion-resistant combustion chamber.  The air then travels up through the oriented flame arrestor plate louvers, where the velocity of the air is increased and its direction altered.  The air then mixes in a normal manner with the supplied gas and is efficiently combusted, producing very low NOx emissions (nitrogen oxides).

In the case where trace amounts of flammable vapors are present in the air flowing into the chamber, the vapors are harmlessly ignited by the burner/pilot flame.  If flammable vapors are in sufficient quantity to prevent normal combustion, the burner/pilot flame is shut down.

Should the flammable vapors continue to the burner, the flame arrestor plate prevents the flames from traveling backwards and igniting vapors outside of the combustion chamber.  The calibrated, multipurpose thermal switch recognizes this and shuts down the pilot and main burner.  This switch also deactivates the burner and pilot in the unlikely event of restricted airflow caused by severe lint, dust, or oil accumulation on the arrestor plate.

“Hot to Properly Inspect a FVIR Hot Water Tank” – Online training video for property inspectors.  http://www.nachi.org/advancedcourses.htm

This blog entry was posted by Ben Gromicko.

Water Leak Catch Pan

August 9th, 2009

A water heater tank should be installed inside a pan in locations in a dwelling where a leak from a conventional hot water tank could cause damage to the structure or property.  The pan is intended to catch water leaks from the tank or associated connections, or condensate from the tank.

The pan should be galvanized steel or other listed material for that use, with a minimum thickness of 24-gauge (0.016 inch) (0.4 mm).  Prefabricated aluminum and plastic pans are common and widely used.  Aluminum and plastic pans may not be allowed by the authority having jurisdiction (AHJ) or code official, because they are not galvanized steel.  Some tank manufacturers require the use of a metal pan only.

A relief-valve pipe terminating into a water leak catch pan is not permitted, because the pan is not an indirect waste receptor.  Most pans have only a ¾ inch-diameter (19 mm) drain outlet, which is not capable of gravity draining the pressurized discharge of the relief valve at full flow.

The pan should not be less than 1.5 inches (38 mm) deep.  The pan should be of sufficient size and shape to catch all dripping water or condensate leaks.  The pan should be drained by an indirect waste pipe having a minimum diameter of ¾ inch (19 mm).  The pan drain must not be reduced in size over its entire length, because a reduction will act as a restriction and will impede the discharge.

The pan must not connect directly to the drainage system.  The pan should terminate over a suitably located indirect waste receptor or floor drain or extend to the exterior.  An air gap must be provided to prevent backflow when the pan drain terminates into an indirect waster receptor or a floor drain.

When the pan terminates to the exterior of the dwelling, it should terminate at least 6 inches (152 mm) and at most 24 inches (610 mm) above the adjacent ground surface.  This makes the pan low enough not to be a nuisance and high enough to prevent the pan drain from becoming blocked by vegetation, snow, and ice.

“How to Properly Inspect Hot Water Tanks” – An online training video for property inspectors.  http://www.nachi.org/advancedcourses.htm

This blog entry was posted by Ben Gromicko.

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