How much diesel does a bunk heater burn overnight compared with idling the truck

A driver on Reddit's r/Truckers asked this week how much diesel a Webasto bunk heater uses per hour to keep the cab warm at about 20°F (minus 7°C). Webasto rates its Air Top 2000 STC cab and bunk heater at 3,100 to 7,000 BTU an hour and 0.03 to 0.06 gallon of diesel an hour, with a battery draw of 14 to 29 watts. The company has stopped building the 2000 STC and now sells the Air Top Pro 25, and it says parts for the older heater will stay available after Dec. 31, 2026.

Idling costs far more. The EPA's SmartWay program puts idle burn for a typical long-haul truck near 0.8 gallon an hour, Heavy Duty Journal reported. The Energy Information Administration's national on-highway diesel average for Nov. 9 was $6.127. Over a 10-hour break the heater burns 0.3 to 0.6 gallon, or $1.84 to $3.68, while idling burns about 8 gallons, or $49.02. In California, where the EIA average was $7.897, the same night at idle costs about $63.18.

California also limits idling. Its rule, 13 CCR 2485, bars diesel trucks over 10,000 pounds gross weight, sleeper cabs included, from idling the main engine for over five minutes anywhere, and caps diesel APU use at five minutes when the truck is parked less than 100 feet from a restricted area. Violators face fines, and the state DMV will not register or renew a vehicle until the violation is cleared, according to the Energy Department's Alternative Fuels Data Center.

A bunk heater warms the cab only. A coolant heater, a separate fuel-fired unit, keeps the engine warm and cuts warm-up idling, the Energy Department says.