At this site, the homeowner has an outside wood furnace to preheat the water entering the water heater. Perry's Plumbing, LLC replaced the gas water heater and installed the radiator and expansion tank. The radiator is used to cool the water entering the water heater to prevent it from triggering the pop-off valve. The expansion tank is used for the incoming cold water. It helps prevents thermal expansion that can trigger the pop-off valve.