Propane vs Diesel vs Electric Heating Off-Grid: Cost Per BTU

Every heating comparison you’ll find publishes a cost-per-million-BTU table, and almost all of them are wrong for anyone heating a vehicle or an off-grid cabin. Not wrong in the arithmetic — wrong in the inputs.

They use the residential bulk price of propane, which is not what you pay to refill a bottle. They assume a furnace efficiency that RV furnaces do not achieve. And they price electricity at the grid rate, which is meaningless if you’re running on a battery bank.

Fix those three things and the ranking changes. Here it is, done properly.

Stated assumptions

We’re showing the working so you can substitute your own numbers, because fuel prices vary enormously by state and season.

Propane pricing deserves a flag. The national average conceals a spread from about $1.64 per gallon in Nebraska to $4.71 in Florida — a factor of nearly three. If you’re doing this calculation seriously, use your state’s number, not the national one.

Cost per million BTU delivered

“Delivered” means heat that actually ends up in the room, after efficiency losses. This is the only comparison that means anything.

Three things jump out.

Diesel wins among the fuels you can carry. It has more energy per gallon than propane, the heaters that burn it are more efficient than RV furnaces, and it costs less per delivered BTU than propane at bottle prices by better than two to one.

Heat pumps win outright when they work. The catch is in that clause, and it’s a large one — RV rooftop heat pumps stop being useful at outdoor temperatures where you most want heat. We’ve covered the temperature floor and why it’s a structural limitation rather than a tuning problem.

The propane furnace you already own is the most expensive option on the list. That deserves an explanation.

Why RV furnaces score so badly

A residential gas furnace is 80–96% efficient. An RV forced-air furnace is typically 60–75%.

The reason is design constraint rather than negligence. An RV furnace is a sealed-combustion appliance: it draws combustion air from outside, burns it in a sealed chamber, and vents the exhaust straight out through the sidewall. Cabin air passes over the outside of that chamber and picks up heat. It’s an inherently safe arrangement — no combustion products enter the living space — and it is inherently lossy, because a substantial fraction of the heat goes out of the exhaust before it can transfer.

There’s no fixing this. It’s the price of the safety architecture, and it’s the correct trade. But it means the appliance fitted as standard to nearly every RV in North America burns about a third more propane than the number on the tank suggests.

What a cold night actually costs

Assume a 24-foot trailer with average insulation, held at 65°F, with an outside temperature of 30°F. Heat loss lands around 10,000 BTU per hour. Over twelve hours that’s 120,000 BTU of delivered heat.

Two gallons of propane a night is why a 20 lb bottle — 4.7 gallons — lasts a little over two nights of hard furnace use in genuinely cold weather. If that matches your experience, your furnace is working correctly and you’ve simply been paying for a physics problem.

Now look at the electric row again: 35.2 kWh. A 400Ah 12V lithium bank holds about 5 kWh usable. Electric resistance heating off a battery is not expensive off-grid; it is impossible off-grid. One 1,500W space heater running eight hours consumes 12 kWh — more than double a large lithium bank, for one appliance for part of one night.

Electric resistance heat is a shore-power appliance. Full stop. Anyone who suggests otherwise hasn’t run the numbers, and running your own numbers on your own loads is exactly what a proper load calculation is for.

The hidden electrical cost of “propane” heat

Here’s the line item that never appears in cost-per-BTU comparisons and routinely wrecks winter boondocking.

An RV furnace blower draws 7–10A at 12V while running — roughly 100W. On a cold night at 40% duty cycle over twelve hours, that’s about 0.5 kWh out of the battery. Every night.

On a 200Ah 12V lithium bank holding around 2.6 kWh usable, that single appliance consumes nearly 20% of your storage per night, before the fridge, the lights, the water pump or anything else. In December, with four peak sun hours on a good day and the array angle working against you, it is entirely normal to run out of battery while the propane bottle is still half full.

By comparison, a diesel air heater draws 1–2A running — around 20W — with a brief 8–10A pull during glow-plug ignition lasting a couple of minutes. Over the same twelve hours, roughly 0.25 kWh including startups. Half the electrical cost of the propane furnace, or better.

This is the strongest practical argument for diesel that has nothing to do with fuel price, and it’s the one experienced cold-weather users make first.

Vent-free propane: cheapest per BTU, and the one that requires respect

Catalytic and blue-flame vent-free heaters score well on the table because nothing goes up a flue — close to all the heat stays inside. They also draw no electricity at all, which in a winter off-grid context is worth as much as the fuel saving.

They achieve this by releasing every combustion product into the space you’re breathing in.

Two consequences follow, and both are serious.

Water vapour. Burning a gallon of propane produces close to a gallon of water. In a sealed, cold vehicle, that condenses on every surface colder than the dew point — windows, walls, the underside of the mattress, inside cabinets. Persistent condensation in a winter rig is a mould problem within weeks and a rot problem within seasons.

Carbon monoxide. Any unvented combustion appliance can produce carbon monoxide, and the risk rises sharply if the burner is dirty, the appliance is faulty, or the space is inadequately ventilated. Two points that get confused constantly:

• An oxygen depletion sensor (ODS) is not a carbon monoxide detector. It shuts the heater off when oxygen falls below a threshold. It does not measure CO and cannot warn you about it.
• A working, in-date carbon monoxide alarm is not optional in any vehicle where an unvented combustion appliance is used. Alarms have a service life, typically five to ten years, and they expire whether or not they’ve ever sounded. Check the date on yours.

If you use one of these, follow the manufacturer’s ventilation requirement — usually a specified opening area — and treat it as a requirement rather than a suggestion. Most manufacturers explicitly instruct that these heaters are not to be left running while occupants sleep. We would go further and say don’t: the cost saving over a vented appliance is a few dollars a night, and the failure mode is not one you get a second chance at.

Our position: vent-free propane is a reasonable supplemental heater for a waking evening in a ventilated space. It is not a primary overnight heating system for a vehicle, whatever the cost table says.

The break-even on a diesel heater

A budget diesel air heater costs $150–250. A Webasto or Eberspächer unit runs $1,200–1,800. Installation — tank tap or standalone tank, exhaust routing, mounting, fuel line — adds $300–600 if you pay someone.

At the numbers above, switching from bottle propane to diesel saves about $4.30 per cold night. Call the total installed cost of a mid-range setup $700.

Break-even: roughly 160 cold nights.

For a full-timer who chases mild weather, that’s two or three winters. For someone doing forty nights of cold-weather camping a year, four years. For a summer weekender, never — and the honest recommendation in that case is to keep the furnace you already own.

The cheap-clone question complicates this considerably, because the economics that make a $200 heater attractive are exactly the economics that produce inconsistent build quality and exhaust components you should inspect before trusting. That’s a separate discussion and worth having before you buy one.

What we’d actually recommend

If you camp in the cold fewer than about forty nights a year: keep your propane furnace. The fuel cost difference doesn’t repay the installation, and the furnace is already there, already legal, already vented. Spend the $700 on the thermal envelope instead — insulation and ventilation improvements return more than any fuel switch, and they reduce your cooling load in summer as well.

If you’re a cold-weather full-timer or boondock through winter: fit a diesel air heater and keep the propane furnace as backup. The fuel saving is real, the electrical saving is larger than the fuel saving in practical terms, and having two independent heat sources in genuinely cold conditions is a safety margin rather than a luxury.

If you’re mostly in campgrounds with electricity included: use it. Nothing on the table beats a marginal cost of zero, and a heat pump or a plug-in resistance heater will preserve your propane for cooking and hot water.

If you’re building a cabin rather than a rig: the calculation changes completely, because a properly specified cold-climate heat pump can hold a COP well above 2 at temperatures where an RV rooftop unit has given up entirely. Different equipment class, different answer.

One closing note on where this sits in the wider budget. Heating fuel is a recurring cost that scales with how you use the rig, and it’s one of the line items most consistently underestimated by first-time buyers. It belongs in your five-year cost of ownership alongside insurance, storage and depreciation — not in the mental bucket marked “small stuff.”

Frequently asked questions

What is the cheapest way to heat an RV off-grid? A diesel air heater, on both fuel cost and electrical consumption, once you’re heating enough nights to repay the installation. Below about forty cold nights a year, the existing propane furnace is cheaper overall because the installation never pays back.

How much propane does an RV furnace use per night? In genuinely cold conditions, one to two gallons — roughly a 20 lb bottle every two to three nights. Milder conditions or a better-insulated rig can halve that.

Can I heat an RV with electricity off-grid? Not with resistance heat. Delivering a night’s heat requires around 35 kWh, which is many times a large lithium bank. A heat pump reduces that by more than half but still needs shore power in practice, and stops working at the temperatures where you need it most.

Is a diesel heater cheaper to run than propane? Yes, by roughly half per delivered BTU at typical 2026 fuel prices, and it draws about a quarter of the electricity that a propane furnace blower does.

Are vent-free propane heaters safe in an RV? They can be used safely with adequate ventilation, a working and in-date CO alarm, and strict adherence to the manufacturer’s instructions — which normally prohibit unattended or overnight operation. They also add significant moisture to the interior. We don’t recommend them as a primary heating system.

Why is my heat pump not working when it’s cold? Because it can’t extract enough heat from cold outside air, and below roughly 40°F its output collapses. This is normal behaviour, not a fault.