RV Propane Runtime Calculator

Inputs

Supply

Cylinder size Number of cylinders Fill level (%)

Furnace

Furnace in use Furnace input rating (BTU/h) Average outside temperature (°F) Thermostat setting (°F) Hours per day furnace is enabled Insulation

Other appliances

Absorption fridge on propane Water heater (minutes of burner per day) Water heater input (BTU/h) Stove and oven (minutes per day) Other (BTU per day: grill, fire pit, generator)

Furnace duty cycle is estimated from the indoor–outdoor temperature difference, assuming a typical trailer needs its full furnace rating at about a 70 °F difference. Real duty cycle depends on wind, sun, and how often the door opens. Fridge consumption uses 1.2 lb/day, a typical figure for a 6–8 cu ft absorption unit on propane.

Constants used

Item	Value
Energy in propane	91,500 BTU per gallon; 21,500 BTU per pound (HD-5 grade, nominal)
20 lb cylinder, full (80% of water capacity)	about 4.6 gal, about 430,000 BTU
30 lb cylinder	about 7.0 gal, about 645,000 BTU
40 lb cylinder	about 9.4 gal, about 860,000 BTU
Absorption refrigerator on gas	about 1,500 BTU/h burner, roughly 1 to 1.5 lb per day in practice
Stove burners	5,200 to 9,000 BTU/h each; 7,000 used for a single burner on medium-high

The furnace estimate, explained

A furnace sized for a trailer runs flat out at design conditions, roughly a 70 °F difference between inside and outside for a typical build. At smaller differences it cycles: 35 °F outside with the thermostat at 65 °F is a 30 °F difference, which this calculator treats as about a 43 percent duty cycle on a typical trailer, and more on a thin-walled one. Multiply duty cycle by the furnace's input rating and by the hours the furnace is enabled and you have BTU per day. The furnace guides cover ignition failures and the cold-air-then-shutdown symptom; how much all of this burns in a week, with tables, is in how much propane an RV uses.

Cold-weather limit

A cylinder can only vaporize propane so fast, and the rate falls with temperature and with how empty it is. A single 20 lb cylinder below about 20 °F struggles to feed a 30,000 BTU furnace continuously, which shows up as a furnace that lights, runs weak, and locks out while the gauge still says there's gas. The calculator flags that combination; the fix is a larger cylinder, two cylinders on an auto-changeover regulator, or a lower furnace duty cycle.