How Much Propane Does a Camper Furnace Use on a Cold Night

It's 2 a.m. in late October, the furnace has kicked on again, and you're lying there wondering whether that 20 lb tank will make it to Sunday. Most camper furnaces burn about 1 to 2.5 gallons of propane on a cold night. A mild night with the furnace cycling now and then can use about 1 gallon. A night near freezing with a big furnace running most of the time can reach 3 gallons. Here's how to work out your own number and how much to bring.

01The short answer

For a typical travel trailer, motorhome or camper van, figure on 1 to 2.5 gallons per night when it's properly cold. On a cool fall night when the furnace only kicks on now and then, about 1 gallon is common. When temperatures sit well below freezing and a 35,000 or 40,000 BTU furnace barely shuts off, plan for around 3 gallons.

A standard 20 lb tank holds about 4.7 usable gallons. That gives you a simple rule of thumb:

• Mild nights: about 4 nights of furnace use from one 20 lb tank.
• Cold nights: only about 1 to 3 days.

Two things decide where you land: your furnace's BTU rating and the weather outside. A small furnace on a 40°F night and a large furnace on a 10°F night are very different.

02The math in plain language

You don't have to guess. You can work out your own number with one label and some division.

Step 1: Find the BTU rating. Look for the label on the furnace itself, usually behind the access panel on the outside wall or in the owner's manual. RV furnaces typically run from about 16,000 to 40,000 BTU per hour. That rating is what the furnace burns while the flame is on.

Step 2: Divide by 91,500. One gallon of propane holds about 91,500 BTU. So a 30,000 BTU furnace running nonstop burns about 30,000 ÷ 91,500 = 0.33 gallons an hour.

Step 3: Multiply by how often it actually runs. A furnace cycles on and off, and the share of time it's actually burning is called the duty cycle. A typical duty cycle runs 30% to 60%. On a very mild night it can be much lower. One worked example has a furnace firing 4 times an hour for 2 minutes each, which is only about 13% of the time. In that case a gallon lasts about 23 hours. Owners on RV forums have estimated that with lows in the 30s and the thermostat at 68, a furnace may run 50% to 75% of the time.

Here's what that works out to over an 8-hour night:

• 20,000 BTU furnace: about 0.5 gal at 30%, 0.9 gal at 50%, 1.75 gal at 100%
• 30,000 BTU furnace: about 0.8 gal at 30%, 1.3 gal at 50%, 2.6 gal at 100%
• 40,000 BTU furnace: about 1.05 gal at 30%, 1.75 gal at 50%, 3.5 gal at 100%

Keep in mind that those figures cover only the 8 hours you're asleep. On a cold trip the furnace also runs in the morning and evening, so a full day can use well more than one night's worth.

03What real campers report

The math gives you a range. Campers on RV forums show what that range looks like on actual trips. Treat these as single reports, since they come from different rigs, furnaces and setups, and not as rules.

• 25°F nights, 50°F days: On a Winnebago owners forum, one owner estimated that heating only with propane in those conditions would use about 2 to 3 gallons per day.
• Same temperatures, one weekend: Another owner with a 31-foot coach said a Friday and Saturday night at those temps burned about a quarter to a third of their tank. That was while using electric heat as much as possible.
• 8°F: One camper in a smaller RV reported about 3 gallons in 12 hours. That was with a small electric cube heater also running and the tanks winterized.
• 18°F: The same camper reported about 1.5 gallons in 12 hours, again with a cube heater helping.
• Big furnace, nonstop: One owner worked out that a 35,000 BTU furnace running continuously would empty 18 gallons in about 48 hours. That's math, not a measurement, but it shows how quickly a furnace that never shuts off uses up a large tank.
• 20 lb tanks in the cold: Another forum owner described a friend's trailer going through a tank about every two days.

On the milder end, one propane-planning guide estimates that a 20 lb tank lasts about 5 to 7 days on a mild fall weekend with light furnace use, and 3 to 5 days in winter with heavy use.

04What changes the number

Why do reports differ so much? These are the factors that move your number up or down:

• Outside temperature. This is the biggest one. The colder it gets, the longer each furnace cycle runs.
• Thermostat setting. Holding 72° overnight uses a lot more than holding 60°.
• Wind. It pulls heat through every seam, vent and window frame.
• Insulation and window covers. Single-pane windows and an uncovered roof vent leak heat fast. Reflective window inserts and a vent cushion help.
• Heated vs. unheated underbelly. Some rigs send furnace heat to the tank and plumbing bay. That protects the pipes, but you're also heating space you don't live in.
• Other propane appliances. A 6-gallon water heater uses about 0.3 gallons a day, and the stove less than that. Both add up over a long trip. Even so, a week of cooking uses less propane than one cold night of furnace heat.

The fuel itself matters too. In deep cold, a tank can't turn liquid into gas as fast, so the usable output drops. Some forum owners also note that propane sold in southern states can contain more butane, which carries less energy per gallon and doesn't vaporize well below freezing.

05How much to bring

Start with your tanks. A 20 lb tank is only filled to 80%, which leaves about 4.7 usable gallons. Many travel trailers carry two. Motorhomes usually have a larger built-in tank, and the same 80% rule applies to it: an 18-gallon tank really holds about 14.

Then plan with a margin:

• Take your nightly estimate and double it. Cold snaps come early in fall, and a forecast low of 35° can turn into 25°.
• Bring a spare tank, or plan a refill stop. On a two-tank trailer, run one tank until it's empty and keep the other full as your reserve.
• Weigh your tanks instead of guessing. Many 20 lb cylinders don't have a built-in gauge. A hanging scale or an inline gauge tells you what's really left. A full tank weighs about 20 lbs more than the empty weight stamped on the collar.
• Don't let tanks run low in the cold. One propane guide suggests keeping them at least 30% full in cold weather.

To use less propane:

• Set the thermostat lower at night. Somewhere in the low 60s or high 50s is common.
• Sleep warm with a good sleeping bag, extra blankets or an electric mattress pad, so the furnace isn't heating the whole rig to living-room temperature.
• If you have an electric hookup, run a small electric heater for most of the heat and let the furnace cover the rest. Many campers say this is the biggest single saving.

Cold-night propane checklist

• Furnace BTU rating noted
• Nightly estimate worked out (BTU ÷ 91,500 × hours × duty cycle)
• Estimate doubled for the trip
• Tanks weighed or gauged before leaving
• Spare tank or refill stop planned
• Window covers and vent cushion packed
• Warm sleeping bag or extra blankets on board
• Small electric heater, if you'll have hookups

If you're planning a fall trip, maybe the long Thanksgiving weekend, do the math before you go. One spare 20 lb tank costs a lot less than a cold drive to the nearest propane fill in the middle of the night.

Sources (6)

• U.S. Energy Information Administration: British thermal units
• Suburban Propane: How many BTUs in a gallon of propane
• CamperFAQs: How much propane does an RV furnace use
• Fogatti: RV propane management calculator
• Winnebago Owners forum: Winter camping propane usage
• RV Forum: Propane question