Auxiliary Heating Systems 101

Essential considerations for choosing reliable, easy-to-maintain units

In a few minutes, the cab interior becomes too cold to occupy comfortably because the engine driven pump is no longer running and circulating hot water to the heater. Autotherm ERS captures this heat and puts it to use warming the cab.


Choices of auxiliary heating systems range from dedicated heaters to auxiliary power units. These can provide not just heating, but air conditioning and other benefits, such as power for "hotel loads" (electricity for in-cab appliances, computers, TVs and personal devices), battery charging and engine warming.

The Pony Pack 200 APU has its own compressor and alternator. If the truck's compressor and/or alternator fails, the APU's compressor and alternator provide enough engine support to allow the truck to continue to function until it can be repaired at a preferred shop, says Rex Greer, president of Pony Pack.

There are APUs that have the ability to provide a combination of engine, cab and fuel pre-heating, John Dennehy, Espar Products' vice president of marketing and communications, says. These effectively remove fuel gelling issues from winter operation.

"Pre-heated engines start easier and dramatically reduce cold start engine wear and cranking system stress for maintenance cost savings," he notes. "Cold start white smoke is eliminated extending the life and regeneration cycles of diesel particulate filters for lower cost of ownership."

"While heating-only units are less costly, an APU with cooling may be a more practical option for truck operators whose routes go through warmer climates," observes Dean J. Lande, manager of business development, Carrier Transicold. "Fuel savings and greater versatility when complying with anti-idling regulations are also benefits with APUs."

Making the appropriate selection of an auxiliary heating system involves a range of considerations. These include such factors as capacity needed based on the climate where the vehicles operate; size of the cab and sleeper compartment; placement, mounting and installation of the system; how the system is integrated into the vehicle; system weight; desired features; and maintenance requirements.


A good starting point for selecting an auxiliary heating system is to figure the expectations of the unit and the operational requirements. Among the types of questions that need to be answered: Will the APU to be used to supply additional power for hotel loads? How much heating and cooling is wanted? What is the heater's capacity?

High BTU (British Thermal Unit) output is important for both heating and cooling, observes Jill Tolstedt, sales and marketing manager, Tridako Energy Systems. The heater's capacity and the outside temperature determine how long it will take a system to heat or cool the environment. The higher the BTU rating, the more fuel that will be burned.

As a rule of thumb, maintaining a comfortable inside temperature when the outside temperature is 32 degrees Fahrenheit requires 20 BTUs for every cubic foot of space.

BTU is a standard unit of measurement used to denote both the amount of heat energy in fuels and the ability of appliances and air conditioning systems to produce heating or cooling. One BTU is the amount of heat required to increase the temperature of a pint of water (which weighs 16 ounces) by one degree Fahrenheit.

A truck sleeper with an 80-inch double bunk sleeper has a volume of 320 cubic feet. Therefore, it would require a heater with 6,400 BTUs. For larger sleepers, or for trucks that operate in extreme cold climates, heaters with much higher BTUs would be needed.

A vehicle's insulation also needs to be considered as well. The poorer the insulation, the more heating/cooling required.

Insulation can be improved by insulating the floors with foam under the carpet, installing extra insulation in the cab and sleeper and adding heavy duty or thermal curtains to separate the sleeper compartment from the cab. These things will also reduce the amount of time it takes for the auxiliary heating system to warm things up or cool things down.


Vehicle application and operation must be analyzed in order to determine how often and how long the truck idles to heat or cool the cab or sleeper, says Pony Pack's Greer.

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