RV propane usage calculator

How to use the calculator

1. Pick your propane supply Choose a 20, 30, 40 or 100 lb tank, or Motorhome tank and type its usable gallons. Built-in tanks have an 80% stop-fill: Manchester Tank lists a 26.2 gallon (water capacity) tank as holding 21 gallons of propane.
2. Set the number of tanks Enter 2 to count two cylinders, or leave 1 to see how long the tank you are on lasts.
3. Tick what burns propane Change the BTU per hour to the input rating on your appliance’s label or in its manual.
4. Enter burner hours per day This is the time the flame is actually lit, not the time the thermostat is on. The hours already in the boxes are example values, not maker figures. Replace them with your own estimate.
5. Read the result You get days of propane, gallons and pounds burned a day, and the biggest user.

How the calculator works

The math has three parts. First it turns your tank into gallons, using Manchester Tank’s figures for its 20, 30, 40 and 100 lb cylinders (4.7, 7.1, 9.5 and 23.8 gallons). For pounds it uses 4.2 lb per gallon, the figure from the Propane Education & Research Council (PERC). Then it adds up the heat you use in a day: each appliance’s BTU per hour times its burner hours, with each one capped at 24 hours. Last, it divides that daily heat by 91,452 BTU per gallon, the U.S. Energy Information Administration (EIA) figure, to get gallons a day. Gallons in the tank divided by gallons a day gives you days.

Here is the default setup: one 20 lb tank with four appliances ticked.

• Furnace (Suburban NT-30SP, 30,000 BTU/h): 30,000 × 6 h = 180,000 BTU
• 6 gallon water heater (Suburban SW6D, 12,000 BTU/h): 12,000 × 1 h = 12,000 BTU
• Fridge on propane (Norcold Polar N7/N8, 1,750 BTU/h): 1,750 × 12 h = 21,000 BTU
• Stove front burner (Greystone range, 8,000 BTU/h): 8,000 × 0.5 h = 4,000 BTU

That adds up to 217,000 BTU a day. 217,000 ÷ 91,452 = 2.37 gallons a day, and 2.37 × 4.2 = about 10.0 lb a day. A 20 lb tank holds 4.7 gallons (Manchester Tank’s figure), so 4.7 ÷ 2.37 = about 2.0 days. The furnace is 180,000 of the 217,000 BTU, or 83% of the propane you burn.

The answer assumes you burn the tank to empty, which a cold tank may not allow (see below).

Propane burn rates for common RV appliances

Gallons per hour = BTU per hour ÷ 91,452. Pounds per hour = gallons × 4.2. These rates apply only while the burner is lit.

Onan rates its generators in gallons per hour, not BTU. Its spec sheet gives 0.6 gallons an hour at half load for the 3,600 W LP version of the QG 4000, and the tool turns that into 0.6 × 91,452 = about 54,900 BTU/h. Load matters: the same Onan burns 0.4 gallons an hour at no load and 0.7 at full load, so size it with our RV generator size calculator.

How much propane does an RV use, and how long does a tank last?

With the furnace running, an RV uses a lot: our example day burns 2.37 gallons (about 10 lb) and empties one 20 lb tank in about 2 days. Take the furnace out and the same tank lasts close to 12 days, because the water heater, fridge and stove only add up to 37,000 BTU a day (0.40 gallons). At the default 2.37 gallons a day, the tank sizes compare like this:

• 20 lb tank: 4.7 gallons, 429,824 BTU, about 2.0 days
• 30 lb tank: 7.1 gallons, 649,309 BTU, about 3.0 days
• 40 lb tank: 9.5 gallons, 868,794 BTU, about 4.0 days
• 100 lb tank: 23.8 gallons, 2,176,558 BTU, about 10.0 days

The weak spot of any propane calculator, ours included, is the furnace hours. No furnace maker publishes how much of each hour the burner stays on. Atwood’s furnace training manual says only that “a furnace should cycle 5-6 times an hour,” which tells you the burner turns on and off, not how long each burn lasts. So furnace hours are your estimate.

How we would pin it down: start a cold stretch with a full tank, note the date, and count the days until it runs dry. Then change the furnace hours until the tool matches. The furnace blower also runs on 12 volt power, so check that side with our RV battery calculator.

Why a tank can quit before it is empty in the cold

Propane leaves the tank as vapor, and a cold, part-empty tank makes vapor slowly. In Atwood’s furnace training manual, a 20 lb bottle that is 40% full can supply about 14,400 BTU an hour at 0°F, less than half of what a 30,000 BTU furnace needs. Atwood says to multiply the 20 lb figures by 1.4 for a 30 lb bottle. Its example for a 65 lb under-mounted tank: at 40% full and 0°F it supplies about 38,500 BTU an hour, which is why a 40,000 BTU furnace in that RV would not fire.

In a cold snap, we would switch to a full tank early rather than run one down to the last few pounds. If the furnace lights and then drops out, our guide to an RV furnace that keeps shutting off covers low gas pressure and the other causes. If it never lights at all, start with RV furnace not working.

Common questions