RV Propane Calculator (Furnace, Fridge, Water Heater & Stove — Days per Tank)
Estimate how long an RV's propane lasts from the furnace duty cycle at your outdoor temperature, the absorption fridge, water heater cycles and cooking — gallons and pounds per day, days per 20 or 30 lb cylinder or onboard tank, and refill cost.
How it works
heat loss ≈ UA × length × ΔT (UA ≈ 6.5 / 10 / 15 BTU/h·°F per ft of rig for good / typical / poor insulation) · furnace duty = loss ÷ (rating × 0.8); BTU/day = rating × duty × 24 · fridge ≈ 1.5 lb/day; water heater = gal × 8.33 × 70 °F ÷ 0.6; stove ≈ 9,000 BTU/h · propane 21,600 BTU/lb, 4.24 lb/gal
RV propane goes four places, and in cold weather the furnace dwarfs the rest: an RV loses heat fast through thin walls and single-pane windows, so the furnace cycles on for a large share of every hour and each hour of burner time is about 1.4 pounds for a 30,000 BTU unit. The absorption fridge sips steadily, the water heater is a few cycles a day, and cooking is small. Turning the duty cycle into pounds per day and dividing into the cylinders tells you how many nights a fill lasts — and, since the blower runs whenever the burner does, how much battery the furnace is eating too.
Worked example
A typical 28 ft trailer at 35 °F outside and 66 °F inside loses about 8,700 BTU/h, so a 30,000 BTU furnace runs about 36% of the time — 12 lb of propane a day on its own. With the fridge (1.5 lb), 12 gallons of hot water (0.5 lb) and 45 minutes of stove (0.3 lb) the total is about 14.4 lb/day: two 20 lb cylinders last about 2.8 days, costing around $12 a day at $3.50 a gallon. The blower also uses about 74 Ah of battery.
Frequently asked questions
How long does a 20 lb propane tank last in an RV?
Running only the fridge and water heater, 2–3 weeks. Add a furnace in freezing weather and a single cylinder can go in a day or two — a 30,000 BTU furnace burns about 1.4 lb per hour of burner time. Weigh the cylinder (tare weight is stamped on the collar) to know what is left.
Why does my furnace seem to run constantly?
When heat loss approaches 80% of the furnace rating the burner never gets ahead. Skirting, window covers, closing off slides or rooms, and a catalytic heater as a base load all help; an undersized furnace in a big rig in deep cold simply cannot keep up.
Is a 30 lb cylinder worth it?
It carries 50% more (7 gal) for a modest weight and cost increase and halves refill trips in winter. Check the tongue weight and the cylinder cover fit; some hitches and covers only take 20 lb bottles.
Related calculators
RV figures are planning estimates. Your coach's data plates (GVWR, GAWR, OCCC), tyre load-inflation tables and appliance ratings govern; weigh the rig loaded at a CAT scale and adjust.