The Takagi Mobius T-M1 water heater works with natural gas or liquid propane. It is rated for 25,000 to 235,000 btu for natural gas and offers a thermal efficiency of 82.3%. With liquid propane, the unit is rated for 25,000 to 225,000 btu with a thermal efficiency of 84.7%. In addition to instant water heating, the unit serves as a heat source for space heating and an air recirculation system, and up to 20 units can be linked together to increase capacity.