Can you use a diesel heater in a tent?

Yes, but only one way: the heater and its exhaust stay outside the tent, and a duct carries the warm air in. Put a carbon monoxide alarm inside. Never set the burner unit on the tent floor, even with its exhaust pipe pushed out through the door. Every maker's manual checked here says the exhaust goes outside, and Webasto's says the heater and exhaust system must not sit where people live.

What a diesel heater is, and the two air paths inside it#

A diesel heater, also sold as a diesel air heater or a parking heater, is a small diesel burner that warms air. It was built to heat a parked truck cab, van or boat. It runs on a 12 volt battery and burns diesel from a small tank.

The key to the tent question is that it has two separate air paths, and they never mix while the heater is sound.

• The combustion path. A small intake pulls in air for the flame. The burnt gas leaves through a metal exhaust pipe. This gas holds the carbon dioxide, water vapour and any carbon monoxide.
• The heating path. A fan pulls in a second stream of air. It passes over the hot outside of a heat exchanger, a metal chamber with the flame inside it, and leaves through the hot air outlet. This is the air you feel. Vevor's manual describes it the same way: fresh air "is heated to hot air through the heat exchanger".

In a van, a fitter bolts the heater through the floor. The burner's intake and exhaust sit under the van, outside. Only the heating air is inside. Webasto's manual asks for the casing to rest "only on the base" with "the base seal" fitted, and Espar's asks for an "air tight seal" at the mounting and every exhaust joint. That seal is what keeps the two paths apart from the people.

A portable or "all in one" unit puts the burner, fan, fuel tank and battery leads in one box with a handle. The box has no floor to bolt through. Set it on a tent floor and the seal the makers rely on does not exist. Every exhaust joint, every gasket and the exchanger itself now sit inside the space you breathe.

What the makers and regulators actually say#

No manual checked mentions tents by name. But four documents from three makers, plus one UK regulator, rule on every part of the setup.

No maker approves a tent. Webasto lists cars, trucks, caravans, motor homes, boats and machinery. And the regulator's complaint was not a faulty burner. It was a box sold without the warnings that would keep a buyer from setting it up inside.

Worked through: one heater outside a family tent#

Take a family tent of about 8 cubic metres, the larger tent used in the Mr. Heater Buddy page. Suppose the night is 0 degrees C with a light breeze of 2 m/s. Put a heater of the Espar Airtronic D2's size on the ground outside, upwind of the door. Its published output is 0.85 kW on Low and 2.2 kW on Boost.

Where the air comes from. Run the heater in what Webasto calls fresh air mode. The fan pulls in outside air, heats it and blows it through a duct into the tent. Webasto's 2000 STC uses a 60 mm duct. Espar lists 19 cubic feet a minute of air on Low and 48 on Boost. That is about 32 and 82 cubic metres an hour. In an 8 cubic metre tent that works out at 4 air changes an hour on Low, and 10 on Boost.

What it does to the oxygen. Nothing burns inside the tent. The flame draws its air outside and its exhaust leaves outside. Compare the Buddy on HI in the same tent. It burns about 510 litres of the tent's oxygen an hour, and it needs about 27 cubic metres of fresh air an hour to stay above its sensor's trip point. The outside heater uses none of the tent's oxygen and pushes in more fresh air than that.

How hot the air is. Each cubic metre of air takes about 1.3 kJ to warm by one degree. At 32 cubic metres an hour, that is about 11.7 W for each degree. So 850 W lifts the air about 73 degrees C before it enters the duct. Boost gives about the same. That is why Webasto wants duct material rated to 130 degrees C, and says not to blow hot air "directly onto living creatures".

How warm the tent gets. Use the heat budget from how much warmer a tent is than outside. Suppose the tent has 18 square metres of fabric, losing 2.7 W per square metre for each degree in a light breeze, or about 49 W per degree in all. The duct air leaves through the vents, taking another 11.7 W per degree on Low.

• On Low: 850 W divided by 61 W per degree is about 14 degrees C above outside.
• On Boost: 2,200 W divided by 78 W per degree is about 28 degrees C above outside.

So on a 0 degree night, Low alone puts the tent in the low teens. The heater's thermostat will spend most of the night near its lowest setting. Over 10 hours, Espar's figures give 1.0 litre of diesel on Low and 2.8 on Boost, with 7 to 28 amp hours from the battery.

Why "safe inside a tent" keeps circulating#

The claim has a true half, which is why it survives.

A well tuned burner makes little carbon monoxide. Espar sets the D2 to 7.5 to 12.5 percent carbon dioxide in the exhaust, and a soot number under 6. A clean flame like that makes mostly carbon dioxide and water, and that is the half the sellers quote.

But the exhaust is not harmless. At Espar's setting, 7.5 to 12.5 percent carbon dioxide is 75,000 to 125,000 ppm. NIOSH sets the level that is immediately dangerous to life at 40,000 ppm. So undiluted exhaust is about two to three times that line before it contains any carbon monoxide at all. The same gas, in a different form, is why dry ice stays out of a tent.

And "well tuned" is the assumption that fails. Webasto's manual lists the signs of a defective unit: "prolonged heavy smoke development", "unusual burner noise", "smell of fuel". It warns that a blocked intake or exhaust "can cause unsafe status of the heater". Espar says the fuel supply needs adjusting for long stays above 1,500 metres. None of that wakes a sleeper. With the burner outside, it happens outside.

The exhaust pipe through the wall is not the van setup. Pushing the exhaust out through a door zip gets the gas outside. It does not give you the sealed base, the clamped and sealed joints or the fixed exchanger mounting the makers require. And it leaves the burner, the fuel tank and a hot casing on a floor of nylon and sleeping bags. The Vevor manual says to keep the heater away from "clothes, or other flammable objects". Espar asks for 2 inches (5 cm) of clearance from anything flammable or heat sensitive.

So the sellers are right that a sound heater with its exhaust outside does not fill a tent with gas. Their error is to treat a box on the floor as sealed, and put it where any leak lands on people.

How to set it up: burner out, warm air in#

1. The heater goes outside, on a firm level base. Not in the porch or vestibule, which shares the tent's air.
2. Point the exhaust away, down and downwind. Vevor says the pipe "cannot be placed upward, but must be placed horizontally or downward". Webasto says the outlet must not be next to window openings or the heating air inlet. In a tent, the door and vents are your windows. Fit the silencer and extend the pipe so the outlet ends well away from both.
3. Feed the heater clean air. In fresh air mode, the heating air intake must draw from "a clean area with no exhaust gases", in Webasto's words. On a portable box the intake and exhaust are a hand's width apart, so this is the step people skip. Put the exhaust on the downwind side and the intake upwind.
4. Duct the warm air in. Pass the duct through a door or a vent opening. Use a duct rated for the heat, since the air leaving the heater can be 70 degrees C hotter than outside. Keep the duct clear of bags and walls, and aim the outlet across the floor, not at anyone.
5. Choose the air mode on purpose. Fresh air mode brings in outside air and pushes stale air out. Webasto says it "renews the cabin air and reduces humidity". Recirculated mode takes air back from the tent through a second duct. It heats faster, but "the humidity is not reduced or the room air not renewed". In a tent full of breathing people, fresh air mode is the better choice. If you recirculate, keep the tent's vents open as tent condensation describes.
6. Power it properly. Vevor asks for a 12 V supply of 15 A or more at start. Espar's D2 draws 8.3 A to start and up to 2.8 A running. Use a battery sized for the night, as 12 volt power and fridges explains. Switch off with the controller, never by pulling the power. Webasto says the fan keeps running after switch-off, and Vevor says the heater takes 3 to 5 minutes to stop completely.
7. Put a carbon monoxide alarm inside. At head height near where people sleep, tested before the trip.

The CO alarm, and sleeping with it running#

The burner is outside, but the hazard can still come in. Exhaust can blow back toward the door when the wind shifts. A drifting cloud can reach the heater's own intake and go straight into the duct. A cracked exchanger would put combustion gas into the heating air. You cannot smell carbon monoxide, and the heater does not measure it. The alarm is the only thing in the tent that does.

CPSC lists the symptoms as headache, dizziness, weakness, nausea, vomiting, sleepiness and confusion. It warns that poisoning "is often detected too late". Each of those only warns someone awake. CPSC says not to use "fuel burning portable heaters or lanterns while sleeping in enclosed areas such as tents". In its 2003 and 2004 estimates, tents, campers and other temporary shelters accounted for about 14 percent of non-fire carbon monoxide deaths, "mostly associated with gas or LP gas heaters". CPSC knows of at least 12 deaths since 2020 from camping equipment including grills, lanterns and stoves.

So our line is this. With the burner and exhaust outside, nothing in the tent burns fuel, and the CPSC warning about heaters inside does not describe the setup. That does not make a night with it running risk free. Run it overnight only with a working CO alarm in the tent and after you have watched it run for an hour while awake. Without an alarm, warm the tent, switch off before sleeping and rely on the bag and pad, as why you sleep cold sets out.

Which alarm? EN 50291-2 covers alarms for "recreational vehicles and similar premises including recreational craft", and adds to the base standard, EN 50291-1. That is the setting closest to a tent. Neither standard is written for tents, so treat either as a backstop, not as permission.

What this page does not cover#

This page covers 12 volt diesel air heaters set up outside a fabric tent. It does not cover heaters fitted into a van, truck or boat by a trained installer, which follow the installation manuals in full. It does not cover wood stoves in hot tents, propane or butane heaters, or petrol versions of the same heaters. The petrol Air Top 2000 STC shares its operating manual with the diesel one.

The setup above applies the makers' rules to fabric. It is not their sign-off, because no maker approves a tent. The heat figures are a model with a breeze and a tent size we chose. Duct losses will make a real tent cooler. The page did not check campground or park rules on fuel-burning heaters. Check those before you arrive. And a heater bought without a manual, or with one that leaves out the ventilation warnings, is the product the UK regulator turned back. Find its maker's instructions before using it at all.

Check it before the first night#

1. Run it outside at home for an hour. Watch for the Webasto signs of a defective unit: heavy smoke, unusual burner noise or a smell of fuel. Any of them means stop.
2. Hold a strip of tissue at the exhaust outlet and at the heater's air intake. The exhaust should blow away from the intake. If the breeze carries one toward the other, move the heater or turn it round.
3. Check the duct's path. Nothing touching it should be meltable, and the tent door should close around it without crushing it.
4. Test the CO alarm, then sit inside for the first hour, awake. The alarm should stay quiet and the tent should smell only of warm air.

Common mistakes#

Pushing the exhaust out and calling it outside. The burner, joints and fuel tank are still inside. Webasto wants the heater and exhaust system out of living areas, not just the pipe.

Pointing the exhaust at the intake. On a portable unit the two are close together. Exhaust drawn into the fresh air intake goes straight down the duct into the tent.

Buying the biggest unit. Vevor's manual lists 2, 5 and 8 kW units. On our model, 0.85 kW already holds a family tent about 14 degrees C above outside in a light breeze.

Skipping the alarm because nothing burns inside. The alarm is there for the night the wind turns.

Frequently asked questions#

Can you use a diesel heater inside a tent?#

Not with the burner unit inside. Webasto says not to install "heater and exhaust system in accommodation areas", and Vevor says not to use its heater "in closed and/or unventilated places". Set the heater outside, send the exhaust away downwind, and duct only the warm air in. Keep a carbon monoxide alarm inside the tent.

Is it safe to sleep in a tent with a diesel heater running?#

Only with the heater and exhaust outside and a working carbon monoxide alarm inside. Exhaust can drift back to the door or the heater's intake when the wind changes, and a sleeper cannot notice the symptoms. Without an alarm, warm the tent before bed and switch the heater off before you sleep.

Can I put a diesel heater in the tent and run the exhaust outside?#

No. The makers' manuals rely on a sealed base and sealed exhaust joints, which a box on a tent floor does not have. Any leak at a joint or gasket then lands in the tent. The burner, fuel tank and hot casing also sit among bags and nylon. Keep the whole unit outside.

Do diesel heaters give off carbon monoxide?#

They can. A well tuned burner makes mostly carbon dioxide and water, but carbon monoxide rises when it runs short of air or goes out of adjustment. The UK regulator says diesel heaters without ventilation expose users to "potentially fatal concentrations of carbon monoxide". Even clean exhaust holds 7.5 to 12.5 percent carbon dioxide.

What size diesel heater do I need for a tent?#

Smaller than the 5 and 8 kW units Vevor lists. On our model, 0.85 kW holds an 8 cubic metre family tent about 14 degrees C above outside in a light breeze, and 2.2 kW about 28 degrees C. A small unit on a low setting, with a thermostat, covers most tents. Duct losses make real results a little lower.

How much diesel does a heater use in a night?#

A heater of the Espar Airtronic D2's size uses 0.10 litres an hour on Low and 0.28 on Boost. Over a 10 hour night that is 1.0 to 2.8 litres. It also draws 0.7 to 2.8 A from a 12 volt battery, plus 8.3 A at start, so 7 to 28 amp hours over the same night.