How Your Caravan Gas Heater Works and How To Use It

If your van came with a gas heater, chances are it will keep you warm through most of a big lap. This guide explains how a caravan gas heater actually works, the flued versus unflued distinction that matters for your safety, its tiny power draw, and how to run one efficiently on the road.

Flued vs Unflued: The Distinction That Matters

Before anything else, you need to know which kind of gas heater you have, because the two behave completely differently when it comes to safety. This is not a technicality. It decides whether your heater is safe to run while you sleep.

A flued heater is a fixed unit, permanently installed in the wall of your van, like a Truma or a Dometic. It burns gas inside a sealed chamber and pipes the exhaust straight outside through a flue. The air it heats never touches the flame, so no combustion by-products, and no carbon monoxide, ever reach your living space. This is the type that is safe to run overnight in a closed van.

An unflued heater is a portable unit, the sort you buy off the shelf and stand on the floor. Radiant heaters with a glowing ceramic panel and catalytic heaters both fall into this group. They have no flue and no exhaust. Every by-product of combustion, including water vapour and carbon monoxide, goes straight into the room you are sitting in. They also burn the oxygen in that room.

How a Flued Gas Heater Works

A fixed flued heater is a genuinely clever bit of kit, and once you understand the layout it is easy to trust. The whole thing is built around keeping the burnt gas and the air you breathe completely separate.

Inside the unit sits a sealed combustion chamber. The heater draws its combustion air from outside the van, burns the LPG in that sealed chamber, and vents the exhaust back outside through a flue in the wall or floor. At no point does the flame have access to your cabin air. Separately, a 12V fan pulls cool air from inside the van, passes it over the hot outside of that sealed chamber, and blows the warmed air back into the living space through ducting. The heat transfers through the metal wall of the chamber, but the gases never mix.

That sealed design is why a Truma or similar can run all night without a second thought. It is pulling its air from outside, dumping its exhaust outside, and only circulating clean, dry, warmed air through the van. A wall thermostat cycles the burner on and off to hold whatever temperature you set.

Power Draw, LPG and Moisture

The two things that surprise most owners about a flued gas heater are how little electricity it uses and how it compares with diesel on moisture.

Barely Touches Your Battery

All the heat comes from the gas, so the only thing drawing 12V power is the fan and the electronic ignition. That means a flued gas heater sips power, typically well under an amp once it is running. You can run one all night off a modest battery and solar setup without making a dent, which makes it a strong option for free camping where you have gas but no mains.

LPG Use and a Little Moisture

A flued heater runs off your standard LPG bottles, the same 4kg or 9kg bottles that feed your cooktop and hot water. Consumption is modest, and a 9kg bottle will see most people through plenty of cold nights, though heavy use in genuinely cold country will have you swapping bottles more often than you might expect.

There is one honest trade-off against a diesel heater. Burning LPG produces water as a by-product of combustion. In a properly flued unit, most of that moisture goes out the flue with the exhaust, so it is nothing like running an unflued heater indoors. But a gas heater still tends to add a touch more humidity to the van than a diesel heater does, because a diesel unit’s combustion is entirely sealed off and vented. If you are fighting condensation on frosty mornings, that small difference is worth knowing.

How To Use It Efficiently

A gas heater rewards a bit of thought. The van is a small, poorly insulated box, so the trick is to keep the heat you make rather than burning gas to replace what leaks out.

Set the thermostat and leave it. A flued heater on a thermostat cycles the burner to hold your target temperature, so there is no benefit in cranking it to maximum then turning it off. Somewhere around 18 to 20 degrees is comfortable for most people and stingy on gas. Take the chill off in the evening rather than trying to run a tropical climate in the middle of a cold snap.

Manage your ventilation sensibly. You need some airflow to keep condensation down, but a window cracked wide open is heat straight out the gap. Small and deliberate is the goal. Insulating your windows with reflective screens or thermal blinds makes a bigger difference to gas use than most people realise, because glass is where most of your heat escapes.

Time your heating. Rather than running the heater through the whole night, many people warm the van before bed, let good bedding do the work overnight, and fire it up again for fifteen minutes before they get out from under the doona in the morning. A warm van at 6am costs a lot less gas than a warm van at 3am when you are asleep and would not notice either way.

Servicing and Safety

A fixed LPG heater is gas appliance and plumbing combined, which means it is not a DIY job. In Australia, a fixed LPG heater must be installed and serviced by a licensed gas fitter. That is a legal requirement, not a suggestion, and it is also what keeps your insurance valid if anything ever goes wrong.

Have the unit checked as part of your regular gas system service, and get any fault, a burner that will not light cleanly, a strange smell, or sooting around the flue, looked at by a licensed fitter rather than pulling it apart yourself. Between services, keep the external flue clear, keep the return-air grille inside the van unobstructed so the fan can breathe, and run a carbon monoxide alarm as a non-negotiable backstop.