This is a 6 gallon heater and heats on LP Gas or 110 volt AC or both. The new Atwood XT RV water heaters use Exothermal technology to deliver more hot water from standard size water heaters. They provide the equivalent of 9 gallons of hot water from a 6 gallon heater. This is accomplished by heating cold water to a hotter temperature and then mixing it with more cold water through an already installed mixing valve on the rear. The result is 50% more hot water.