The gas heater will consume approximately one gallon of propane for each hour it runs. Keep in mind your heater doesn’t run 24/7 just because you have your system on. Like the furnace in your home, it has a thermostat and turns on intermittently to maintain the water temperature you have the system set to. Obviously the higher you have your thermostat set to, the colder it is outside, and the less the water is insulated from heat loss, the more time your heater will spend running. We recommend having at least a 120-gallon (aka 420 lb) propane tank. These tanks resemble an upright barrel and are about 4″6″ tall and 30″ in diameter. When full these tanks hold 96 gallons of fuel and typically will supply a hot tub’s need for at least a month. Keep in mind this can vary a lot and in extreme cases, this tank might be inadequate. However, for most scenarios, this tank size is adequate. Bigger tanks will simply give you more peace of mind and more time in between fillings.