There are two types of gas water heaters used in Sun City. Up until about 2003, an open combustion-chamber water heater was used. Starting in 2003, the sealed combustion-chamber unit, aka Flammable Vapor Ignition Resistant (FVIR), was used. The purpose of the new safety standard is to prevent the ignition of any flammable liquids spilled or stored near a water heater. In the older open-combustion chamber water heaters, the combustion air entered directly into the combustion chamber.
