September 25, 2026 Colby Hill

Winter Camp Heat: Carbon Monoxide, Propane, and What Freezes First

The mistake happens in the first ten minutes of setting up camp

You get to the trailhead late, it's already below freezing, and the fastest way to feel human again is to zip the tent or the camper shell closed and light a heater. That instinct is the whole problem. A winter camp setup doesn't fail because people bring the wrong gear. It fails because they treat heat, air, and cold-soaked electronics as one problem, when they're three separate ones that break in a specific order, and the failure mode for the first one is not "you're cold" — it's carbon monoxide poisoning while you sleep.

This isn't a sleeping-bag or tent article. R-value, condensation, and ground insulation are their own subject and worth reading on their own. This one is about the systems around the sleep system: what's burning fuel or drawing current in camp, what stops working first when the temperature drops, and what order things actually fail in so you can plan for it instead of finding out at 2 a.m.

Carbon monoxide is the one that kills, not the one people worry about

Most people worry about the tent catching fire. The real risk with a fuel-burning heater in an enclosed space is carbon monoxide, and it's more dangerous specifically because it doesn't announce itself. CO is odorless, it doesn't trigger a smoke detector, and by the time you're symptomatic — headache, drowsiness, confusion — you're already impaired enough that acting on it gets harder, not easier. It kills campers in enclosed tents, truck canopies, and rooftop tents every winter, and it's almost always a heater that was working exactly as designed.

A few things that trip people up specifically because they sound like solutions:

"Indoor safe" doesn't mean "seal it up." Portable radiant and catalytic heaters rated for indoor use are tested and rated with a minimum ventilation requirement in the manual — usually a specific window or vent opening left cracked. That rating is conditional, not unconditional. Zip the tent fully closed with one of these running and you've voided the assumption the rating was built on.
Cracking a window is not the same as meeting the spec. A couple inches of gap in a big canvas tent and a couple inches of gap in a truck canopy with a quarter of the air volume are not equivalent. Go by the manufacturer's stated ventilation opening, not by what feels like enough air.
Altitude changes combustion. Thinner air means less oxygen per breath of fuel burned, which increases CO output from the same heater compared to sea level. A lot of winter wheeling happens above 7,000 feet, where this actually matters.
Running the vehicle for cabin heat has its own version of this. If you're using the truck itself as the warm box, snow packed or drifted against the tailpipe can push exhaust back into the cabin through the underbody. That's a driving and trail-recovery scenario, not a static camp one, and it's covered from that angle in our winter wheeling guide.

The fix is not complicated: use a battery-powered CO detector independent of the heater itself, keep the ventilation opening the manual specifies, and never treat a fuel-burning heater as safe to run while everyone's asleep unless the manufacturer explicitly rates it for that with the vent configuration you're actually using.

Matching the heater to the setup

Catalytic and radiant propane heaters

These are the small portable units most people already own. They're simple, don't need power, and produce real heat from a small canister. Their limitation is exactly the ventilation issue above — they're unvented, meaning combustion byproducts go into the same air you're breathing, by design. They belong in a space sized and vented the way the manual says, not in whatever tent you happen to own.

Forced-air propane and diesel parking heaters

Vehicle-mounted parking heaters (the diesel- or gas-fired bunk heaters used in overland builds) draw combustion air from outside and vent exhaust outside, then blow warmed air into the cabin or canopy through a sealed duct. Properly installed, this is the safer category for sleeping through the night, because the combustion loop never touches your breathing air. The tradeoffs are installation complexity, a fixed mount, and a constant (if small) parasitic draw on the battery for the fan and glow plug, even though the heat itself comes from fuel and not electricity.

Electric heaters

No combustion, no CO risk, but the math rarely works. A small electric space heater draws enough current that even a healthy dual-battery setup runs dry in a few hours unless you're plugged into shore power or running a generator, and running a generator overnight brings its own carbon monoxide exhaust-placement rules right back into the conversation. Electric heat is realistic for short bursts — warming the cab before you get moving — not for holding a tent at temperature through an eight-hour night.

What freezes first (and what actually happens when it does)

Cold doesn't hit every system in your rig at once. In practice it goes roughly in this order.

Exposed water lines and pumps, first

Any water sitting in a hose, a pump housing, or an exposed fitting freezes well before a full tank does, because thin-walled lines have almost no thermal mass. A frozen pump housing can crack from ice expansion even if the tank behind it is fine. If you're running an on-board water system in freezing conditions, drain the pump and exposed lines when you're done for the day rather than leaving them charged, and if the system stays in service, look at heat trace tape or pump insulation rather than assuming "it's inside the canopy" is enough protection. Jugs and jerry cans are actually more forgiving here — a sealed jug freezes from the outside in and gives you time to notice, where a pressurized line can split before you'd ever see it.

Propane, rarely all the way frozen, but the regulator can ice up

Propane itself doesn't fully stop vaporizing until you're deep into sub-zero territory, well past what most people are camping in. The more common failure is a regulator icing internally from trace moisture in the gas or the humidity in the air around the regulator body, which drops output pressure and starves the appliance right when you're pulling the most flow — lighting a heater on a nearly empty tank in cold weather is the classic way to trigger it. Keeping tanks more than a quarter full through winter and keeping the regulator itself shielded from direct wind and precipitation avoids most of this.

Batteries and the fridge, on their own timeline

This is the one that surprises people who've done the CO and water math and think they're covered.

Lithium (LiFePO4) house batteries generally will not accept a charge below freezing. Most battery management systems on LiFePO4 packs cut off charging around 32°F (0°C) to protect the cells from lithium plating, even though the same battery will happily discharge in the cold. That means your solar panel or alternator can be putting out full current and the battery still won't take it — a battery monitor showing a flat state of charge on a sunny cold morning isn't a wiring fault, it's the BMS doing its job. Some packs include internal heating pads specifically to work around this; if yours doesn't, an insulated battery box helps it hold residual heat from the day's charging longer into the night.
Lead-acid and AGM batteries lose usable capacity in the cold rather than refusing to charge, which is a different failure mode and the one covered from the vehicle-starting-battery side in our winter wheeling guide — this is about the house/auxiliary side of the system, running the fridge and lights, not cranking the engine.
Fridge compressors don't like being cold-soaked either. Compressor lubricant thickens in low ambient temperatures, and a fridge mounted in an unheated bed or trunk can struggle to cycle normally overnight. The counterintuitive result: people lose food to freezing, not spoiling, because the thermostat is reading a cold ambient and the compressor behaves erratically trying to compensate. A thermometer inside the fridge, not just trust in the dial, catches this before your food does.

A working order for setting up a winter camp

Park and level before your hands get cold enough that it becomes hard to do carefully — this is a small thing that gets skipped and makes everything after it worse.
Set the CO detector first, before any heater goes on, and confirm it's independent of the heater's own power.
Run any fuel-burning heater with the ventilation opening the manual specifies, not by feel.
Drain or protect exposed water lines and the pump if you're not actively using the system.
Check propane level before committing to an overnight burn; top off or swap a tank under a quarter rather than pushing it.
Put a thermometer in the fridge and check it before bed, especially in an unheated bay.
If you're relying on solar to recover battery charge overnight losses, understand that a cold lithium pack may not accept it until the pack warms up the next day.

Five mistakes worth avoiding

Running an unvented catalytic or radiant heater fully sealed up "just for a little while" while people are asleep.
Assuming a cracked window is equivalent across every tent size and shape.
Lighting a heater off a nearly empty propane tank in cold weather and blaming the appliance when output drops.
Leaving a charged water pump and lines pressurized overnight in freezing temperatures because "it's inside the canopy."
Trusting a battery monitor's percentage instead of understanding that a cold lithium BMS may be refusing the charge entirely.