Winter warmth
Staying warm without idling: bunk heater vs APU vs 12V blanket
Short answer: a diesel bunk heater wins for most drivers — it sips a tenth or two of a litre per hour and keeps the whole sleeper warm. An APU does more but costs far more. A 12V electric blanket keeps you warm for a few amps, not the cab. Idling works too, at roughly 30 litres of diesel a night.
Research-based. We did not test these hands-on. Scores come from published specs and driver reviews.
Key takeaways
- Idling burns roughly 30 litres a night. About $40–50 at current pump prices, plus soot, oil dilution, and possible idling fines.
- A diesel bunk heater sips 0.1–0.2 litres per hour. It holds the whole sleeper through a −30°C night for a rounding error next to idling — the standard answer for a reason.
- A 12V blanket warms you, not the cab. Roughly 45–50W (about 4 amps) on a timer: the backup and the supplement, never the whole strategy.
- Test the heater in October. A heater that dies in October is a service call; in January it is an emergency. And never heat a sealed sleeper with unvented combustion — carbon monoxide kills.
The baseline
Idling: the expensive default
A heavy truck burns roughly 0.8 gallons of diesel per hour at idle — about 3 litres. Over a 10-hour rest that is roughly 30 litres, or on the order of $40–50 at current pump prices, every single night. Across a winter, that is thousands of dollars converted directly into noise and exhaust.
It also wears the engine: extended idling builds soot, dilutes oil, and shortens service intervals — the engine is designed to work under load, not to lope all night. And many cities and jurisdictions restrict idling outright, with fines that make the fuel look cheap. Idling is the fallback every driver should have, and the plan no driver should rely on.
The favourite
Diesel bunk heater: the driver’s favourite
A diesel-fired air heater (Webasto and Espar are the names you will hear) is a small furnace plumbed into the sleeper: it burns diesel from your tanks through a heat exchanger and blows warm air into the bunk. Fuel use is tiny — roughly a tenth to two-tenths of a litre per hour, a rounding error next to idling.
It runs off the truck’s batteries for the fan and glow plug, drawing only a couple of amps once started, and it will hold a sleeper at a comfortable temperature through a −30°C night. The catch: it has to be installed and maintained. The number-one winter rule from the winter cab comfort checklist applies here — fire it up for a full night in October. A heater that dies in October is a service call; a heater that dies in January is an emergency.
The upgrade
APU: heat plus power, at a price
An auxiliary power unit is a small diesel engine mounted on the truck that generates electricity and heat without running the main engine. It charges your batteries, runs the HVAC, and powers cab appliances — the full hotel load. Fuel use is a fraction of idling, and it solves the battery-drain problem from our overnight cooler guide at the same time.
The catch is the price tag: several thousand dollars installed, plus its own maintenance schedule. APUs make sense for owner-operators running year-round and for fleets spec’ing trucks — they are rarely something a company driver chooses. If your truck has one, learn its controls before the cold; if it does not, you are not buying one off Amazon.
The backup
12V electric blanket: personal warmth, small draw
A 12V heated blanket draws roughly 45–50W — about 4 amps — and warms the person under it, not the cab around them. On a night when the bunk heater is struggling or you are caught without one, it is the difference between sleeping and shivering. Run it on a timer so it is not pulling all night.
Two rules, both non-negotiable: one high-draw 12V heater at a time on a circuit you trust, and never leave a heating element unattended. Blankets, seat heaters, and 12V kettles each pull serious amps — stack them and you are hunting blown fuses at midnight. And a blanket does nothing for the cab itself: your drinks, electronics, and food still face the full cold (see what freezes in a parked cab).
Layering
The layering play: when the heater is not enough
Every veteran winter driver layers heat the way hikers layer clothing. A sleeping bag rated for −30°C over the bunk mattress. Bunk curtains closed to shrink the heated space. A mylar emergency blanket as a final layer — ugly, crinkly, and shockingly effective. Heavy socks and a toque for the 3 a.m. bathroom run.
None of this replaces a working bunk heater. All of it together can carry you through the night the heater picks to die — which, per Murphy, will be the coldest night of the year, forty kilometres from the nearest town.
Head to head
Head to head
Diesel bunk heater
Heats the whole sleeper for ~0.1–0.2 L of diesel per hour. The standard answer for a reason — if your truck has one, this is the plan.
12V electric blanket
Warms you, not the cab, for ~4 amps. The backup plan and the supplement — never the whole strategy on a −30°C night.
The bunk heater is the plan; the blanket is the insurance. In a straight fight for keeping a sleeper livable at −30°C, the heater wins walking away — the blanket wins the only contest it enters: cheapest backup warmth you will ever buy.
Safety
The carbon monoxide warning
Never run an unvented combustion heater — propane buddy heaters, catalytic heaters, candles for warmth — in a sealed sleeper. Carbon monoxide is colourless, odourless, and it kills drivers every winter. A diesel bunk heater is vented to the outside by design; a propane heater from the camping aisle is not. If your heat source has a flame and no exhaust pipe leaving the cab, it does not belong in the cab. No exceptions, no “just for a few minutes.”
FAQ
Cab heat questions, answered
How much fuel does idling use overnight?
Roughly 0.8 gallons (about 3 litres) per hour — around 30 litres over a 10-hour rest, or roughly $40–50 a night at current diesel prices. A diesel bunk heater does the same job on a tenth to two-tenths of a litre per hour.
Can I use a propane heater in my truck sleeper?
No. Unvented combustion heaters produce carbon monoxide, which is colourless and odourless and kills drivers every winter. Only use heaters vented to the outside — a diesel bunk heater is designed for this; a camping propane heater is not.
How much power does a 12V electric blanket use?
Roughly 45–50W, about 4 amps at 12V. That is manageable for a truck battery bank overnight, but run one high-draw heater at a time, on a circuit you trust, and never leave it unattended.
Will a 12V blanket keep the cab warm?
No — it warms the person under it, not the air. Your drinks, food, and electronics still face the full cold. Pair it with a real heat source, and see what freezes in a parked cab for the rest of the plan.
When should I test my bunk heater?
October, for a full night, before you need it. A heater that fails in October is a service call; a heater that fails in January is an emergency. This is the single highest-leverage item on the winter cab comfort checklist.
How this guide was made
Research-based. We did not test these hands-on. Scores come from published specs and driver reviews.
We worked from manufacturer specifications for diesel-fired bunk heaters and 12V heated blankets, published driver-review aggregates, and standard diesel consumption figures at idle, as of September 2026. Nothing here was tested hands-on — the comparisons reflect published specs and what working drivers report.
Keep reading
Keep reading
Winter cab comfort checklist
The full cold-weather cab setup — test the bunk heater in October.
Read the guide →
Winter
What freezes in a parked cab overnight
What the cold does to everything the heater is not protecting.
Read the guide →
Winter
12V cooler overnight battery drain
The amp-hour math for everything else you run overnight.
Read the guide →