Auxiliary Heating Systems 101

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

For a driver that will be spending a night in his truck every other night or so, a battery-powered auxiliary heating system that can provide up to 8 hours or so of operation might suffice, he says. On the other hand, a driver who will have to do his 34-hour Hours-of-Service reset in his truck will need a much larger capacity system.

Trucks running in the arid Southwest will have different heating and cooling requirements that those operating in the Northwest Territories, he adds.

It is also advisable to compare the airflow of auxiliary heating systems, measured in cubic feet per minute (cfm), as well as their fuel consumption, measured in grams per hour (gph).

Driver-friendly controllers with temperature display and the ability to have on-board diagnostic code display are good features to have on an auxiliary heating system, says Espar Product's Dennehy.

"The whole idea behind idle reduction is to reduce fuel consumption by using engine-off heating and cooling products instead of idling the engine for bunk comfort," states Josh Lupu, marketing specialist-commercial vehicle market, Webasto. "Check the specifications of the heater or cooling system you choose to make sure you are choosing one with low fuel consumption."


Deciding upon where to mount an APU is another essential consideration. Typically, APUs are mounted on the frame rails. A favored location is between the fuel tank and the rear wheels. They may also be mounted under the step.

One of the potential problems to be aware of is that the underside of the chassis is a location that is constantly bombarded with dirt and grime. During winter, the chassis is subjected to de-icing chemicals that road crews use on roadways to help make them passable. These chemicals tend to accelerate vehicle corrosion.

Because APUs typically hang low to the ground, road de-icing chemicals can get into their electronics and cause problems with their electrical systems, Greer of Pony Pack points out. His company is working to develop an all-mechanical APU to eliminate this issue

Where the unit is placed on a vehicle will impact accessibility of the unit for daily checks and serviceability. The more difficult it is to get to a unit, the greater the likelihood that routine maintenance checks, especially by drivers, won't be done as often as they should be.

System placement also has an affect on vehicles aesthetics.


One of the chief maintenance issues that factors into the buying decision is ease of serviceability and straightforward maintenance.

"Make sure you know up front what is required to keep the idle reduction solution functioning properly," Webasto's Lupu says. "Replacement belts, pulleys, oil changes, etc., add to the cost and length of time that you see a return on investment."

Routine fluid and maintenance checks should be easy to complete, adds Tolstedt of Tridako Energy Systems. Its Power Cube APU, for instance, has two lid options. The standard lid has a couple removable straps and the whole lid comes off for access to the unit. The fleet maintenance service hatch has an easy-open lid for routine fluid checks.

"Basically, if you follow the manufacturer's suggested maintenance schedules you should expect the proper performance from your unit," Mike Shikany, director of sales and marketing, Willis Power Systems, notes. Its unit is designed so that the routine maintenance can be done alongside maintenance on the truck, thereby eliminating extra downtime.

"The most important part of keeping any auxiliary component running as designed is appropriate inspection and follow up," he emphasizes. "Keeping the unit properly serviced and inspected at appropriate intervals is essential."

So is keeping the unit clean. If the components, especially filters, are clean and unobstructed, they will perform as designed.

"Loose bolts, nuts, connections and components are a common problem on any machine working several thousand hours a year and all such items should be inspected regularly to determine their condition," says Shikany. "In addition, all combustion-driven APUs have belts that need to be inspected regularly."

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