The Bradford White Defender FVIR (Flammable Vapor Ignition Resistant) System is by far the best available on the market today. Other Manufacturers have struggled with design and reliability problems including one that resulted in a class action settlement. FVIR is a safety system for gas water heaters that prevent the water heater from becoming an ignition source for vapors from spilled flammable liquids. As of July 1, 2003, 30, 40, and 50-gallon, gas-fired water heaters built for sale in the United States were required to have FVIR protection with others phased in over time.
A simplified description of how FVIR Technology works is that older designs had an open combustion chamber where combustion air is drawn in at the base of the water heater. When a flammable liquid was spilled or used in the area of the water heater flammable vapors would accumulate along the floor and if the vapors reached the pilot or burner flame in the correct proportions they could ignite and burn back to the area where the flammable liquid was spilled or, being used, causing an explosion and or, fire. The FVIR technology encloses the combustion chamber of the water heater and draws the combustion air through a flame arresting device where it is used for the pilot and burner. There is also a device that senses if the flame is too tall or, overheating either from a lack of proper combustion air or, too much fuel caused by flammable vapors entering the unit. Improper flue venting may also affect the temperature in the burner area. In any case when an unsafe burner condition, or FVIR event is noted the sensor shuts off the gas supply to the burner and pilot flame preventing ignition of the flammable vapors.
Virtually every water heater manufacturer other than Bradford White has had problems in one form or another that result in their customers either having to face excessive maintenance and repair costs, unreliable operation, or even replacement of the water heater in some cases.
One manufacturer had a thermocouple with a thermal fuse built in that had a reverse thread. This thermocouple when tripped was required to be replaced and was unavailable except through the manufacturer requiring a wait for the replacement parts, and if you wanted it faster there was a substantial cost for expedited shipping. This resulted in a class action lawsuit and a fix involving replacement of the burner assembly to one which used a thermal device with a reset switch and a design change for the new production units.
Some of the manufacturers have the combustion air drawn in through a small screen on the bottom of the water heater only a small distance above the floor. This design has faced problems with the screen clogging with dust and lint causing a lack of proper combustion air and tripping the sensor. This problem was amplified by the fact that water heaters are typically installed in laundry areas, closets and basements which are typically high lint and dust areas and the fact that the screen is located under the unit near the center and is difficult to access to clean when the water heater is set in the code required pan.
Another manufacturer has the combustion air inlet on the side of the unit but it is low between the bottom of the water heater and the combustion chamber door this is only slightly better than the bottom of the unit in terms of getting it away from the high dust area at floor level. It also requires replacement of the pilot assembly once the FVIR sensor has tripped.
Yet another manufacturer has a design which I consider to be second best as it has the combustion air inlet up on the sides which is good but does not have a reset for the FVIR sensor. Tripping of the FVIR sensor requires replacement of the pilot assembly. Fortunately for their customers the likelihood of dust and lint clogging the flame arrestor is greatly reduced by the height of the combustion air inlet and the pilot assembly is readily available.
Only the Bradford White Defender FVIR System brings all the right stuff to their design. They have the combustion air inlet high on the side of the unit where cleaner air is drawn into the unit keeping the flame arrestor from clogging with lint and dust. The design of the flame arrestor has larger openings that rely on velocities of the air flow and changes in direction to provide the flame arresting function giving less likelihood of lint and dust clogging over the screen design. A reset button is provided for the FVIR sensor so no parts replacement is required if there is an FVIR event. This combination of features makes Bradford White Defender FVIR Water Heaters my pick for the best FVIR water heaters. They are by far the lowest maintenance, highest in reliability, & lowest in repair frequency among the FVIR gas water heaters available. Whether or not you have hot water in the morning should be the last thing on your mind, yet sadly for many people, it is something they have to worry about.