“Idle reduction is a cost saving strategy and a driver comfort issue.”

A large U.S. fleet

Executive Summary

Fuel-operated or diesel-fired heaters allow fleet owners to provide heat to truck cabs. They are inexpensive to purchase and maintain and some models eliminate engine cold start. However, they have limited functionality and don’t address cooling or AC power requirements. 

Fuel-operated or diesel-fired heaters use diesel fuel to blow heated air (or circulate heated coolant) into the cabin (or engine) to improve the environment during cold weather conditions.

There are two kinds of fuel-operated heaters:

  • Fuel-operated air heaters1
  • Fuel-operated coolant heaters2
  • 1. Also know as bunk heaters, fuel-operated air heaters act like small furnaces with a heating element and blower providing cab heat via direct ducting or via the truck’s factory-installed HVAC ducting. Heating capacities range from 6,800 to 13,600 Btu/hour. The units draw 0.7 to 11.2 amps of battery power when in use.
  • 2. Fuel-operated coolant heaters provide engine pre-heat, and act like hot water furnaces. They use the truck’s supply of diesel fuel to produce the needed heat. Heat output ranges from 17,100 to 45,000 Btu/hour. Electrical consumption ranges from 1.9 to 7.5 amps.
Introduction to Idle Reduction
Common Fleet Strategies
  • Fuel-operated air heaters were found to be one of the anchor technologies fleets use as part of their idle-reduction strategy.
  • Using a fuel-operated air heater as the anchor technology, and focusing on setting engine-operating parameters, driver training, and driver incentives is the least costly way to keep drivers warm. 
  • A fuel-operated air heater coupled with a diesel APU and an inverter for HVAC will result in using the least amount of fuel to meet idle-reduction goals. The diesel APU is the anchor technology here.
  • A fuel-operated air heater coupled with a battery HVAC and additional insulation will most efficiently cover all climate zones. The battery HVAC is the anchor technology here.
  • A fuel-operated air heater and an inverter/battery charger along with truck stop electrification provide heat and AC power to run hotel loads, but do not provide cooling. Truck stop electrification is the anchor technology here.
What Others Are Saying
Decision-Making Tools

There are already a wide variety of payback calculators for any given type of idle-reduction system. In an effort to meet the industry’s need for more information, we have also developed a high-level payback equation to aid fleets in choosing the right combination of technologies.

Decision-Making Tools


Every truck manufacturer offers optional fuel-operated heaters. Here is a breakdown of who offers what:

  • Freightliner offers Espar
  • Western Star offers Espar and Webasto
  • Peterbilt and Kenworth offer Espar
  • Volvo and Mack offer Webasto
  • International offers Espar and Webasto

Fuel-operated heaters are relatively inexpensive both to purchase and maintain. They are offered as factory-installed options and integrate with other idle-reduction technologies.

Coolant heaters are often required in trucks operating in colder climates and are sold in conjunction with other idle-reduction technologies.