Auxiliary Heating Systems 101

Anti-idling laws, high fuel prices and unnecessary engine wear are causing fleet operators to look for alternative ways to keep drivers in a comfortable environment when temperatures drop. The use of auxiliary heating systems is one method for heating the truck cab and sleeper without having to run a truck's engine.

While an idling engine maintains a comfortable environment for drivers, it wastes energy. Even though diesel engines are efficient when idling, constantly running high horsepower engines at low rpm combusts fuel incompletely. What's more, continually operating the engine at low speed causes additional wear on internal parts compared with road speed rpm, and that increases maintenance costs and shortens engine life.

By using an auxiliary heating system to heat the cab, a truck's engine can be shut off, so far less fuel is used and fewer diesel emissions emitted. Since the engine isn't running as much, there is reduced the wear on the engine and other related mechanical components.

On average, heavy duty diesel truck engines consume 1 to 1.5 gallons of diesel fuel per hour while idling. When operating on the road, these engines consume around 6 or more gallons per hour.

The amount of operational savings that can be realized from auxiliary heaters will depend, naturally, on how well the system is matched to requirements and needs. That is no small feat, as there is a very wide variety of designs and models to pick from.

There are auxiliary cab and sleeper heater systems that come with engine heating capability, and full auxiliary power units (APUs) that come with added functions as well. APUs are offered by truck OEMs as original equipment and from a variety of manufacturers for new and aftermarket installation.

APUs come in various styles and arrangement. There are models that are powered by diesel or propane. The typical major components are a small engine, an alternator and the heating, ventilating and air conditioning (HVAC) system.

There are hybrid and electric APUs for which batteries and an inverted charger are important components. One hybrid system, introduced earlier this year, combines the Bergstrom NITE Plus System no-idle climate control system with a Kohler DC power unit.

With this hybrid system, when the power levels of the four deep-cycle AGM batteries decrease to low voltage levels, the low-battery indicator is triggered and the Kohler DC power unit begins to recharge the batteries while keeping the Bergstrom NITE Plus System operating uninterrupted, explains Stacy Peshkopia, marketing manager, Kohler Power Systems. Should the truck's batteries also be depleted, the power unit is able to recharge them with the use of the specified bi-directional separator, and at no risk of overcharging either bank of batteries.

In heating mode, 0.05 gallons per hour are consumed, she says, while 0.10 grams per hour is used when the hybrid power system is in recharge mode. When the system is in the air-conditioning mode, it uses no fuel because it operates solely on the Bergstrom system.

Some vehicle APUs can also use an external shore power connection for their heating and cooling functions. Fuel-cell powered APUs as a way to reduce idling on large trucks is under development and has been demonstrated.

Another alternative heating solution is the Autotherm Energy Recovery System (ERS). It automatically continues operation of the vehicle's heater every time the engine is turned off.

By circulating the same amount of hot water to the cab heater as the engine pump and keeping the fan operating, the Autotherm ERS keeps the cab interior warm for hours whether the operator is in the vehicle or out of it, says Frank Perhats of the Autotherm Division of Enthal Systems.

The cooling system of any vehicle that has been driven on the road for a half hour or longer has reached optimum operating temperature and is, therefore, a storehouse of useable energy, he explains. In most trucks, this energy is slowly dissipated to the vehicle exterior when the engine is off.

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.

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."

Carrier Transicold's Lande also advises looking at the manufacturer's recommended maintenance intervals. "Some units, such as Carrier's ComfortPro APU, provide service intervals of 1,000 hours of operation, which provides plenty of flexibility for synchronizing service with the truck's service schedule," he says. "In typical long-haul operations, 1,000 hours of APU use equates to about six months, so at that rate, service will be needed twice a year."


"The more complex the unit is to install, the more time and, consequently, cost for putting it in," says Lande. "Likewise, it's worth checking the accessibility of the unit's components for ease of service and repairs."

"The robust nature, construction, proper assembly and professional installation of any unit is very important," Shikany adds. "My suggestion is look around, check the options and most importantly, put your eyes on the unit before you make a purchasing decision."

Poor installation has a major impact on the operation, performance and reliability of any unit. With some auxiliary heating system manufacturers, installation by anyone other than an approved installer could void the system's warranty.


Reliability is yet another key factor in making a decision to purchase one auxiliary heating system rather than another.

This is especially the case for tractors traveling across the country, points out Carriers Transicold's Lande. A large dealer network and nationwide service support is critical for such applications so there is the ability to have work performed nationwide.

The stability and reputation of the manufacturer is also important, adds Tridako Energy Systems' Tolstedt, and "service needs to be reliable, available and convenient."

"You expect that the solution you buy will have the utmost quality and durability," says Lupu of Webasto. "But what if something unforeseen happens where you need service or repair? If you're on the road, you want to be able to find an authorized dealer or repair facility and get back on the road quickly with as little downtime as possible.

"With rising fuel prices and the demand for idle reduction devices, new companies are popping up every month," he continues. "Make sure the solution you buy is backed by company with a history rooted in heating and cooling, and that the company will be there if you need service."


Warranty coverage, both in terms of the length and major component coverage, is one more matter to keep in mind, recommends Lande. Extended warranty service plans are sometimes available and could be a good insurance policy to help protect the investment in an auxiliary heating system.

"Large interstate and national carriers should strongly weight the availability of parts and service through a dealer network that spans their entire operating region," he suggests.

"Make sure you fully understand the warranty," adds Lupu. "In the event that a problem does occur, you want to be covered. Check the length of the manufacturer's warranty and make sure you're not being short changed."


The return on an investment in an auxiliary heating system depends on a number of variables, including type of system, its capacity, length of time in use, cost of fuel and how the system will affect overall truck performance.

Figuring cost savings in fuel usage is a common calculation when considering an APU, says Tridako Energy Systems' Tolstedt. Instead of idling the truck engine all night for heating or cooling and other power needs, an APU can do the job and consume less fuel.

The U.S. EPA SmartWay Transport program estimates that long-haul trucks outfitted with an APU save an average 8 percent in fuel costs each year.

In addition to these savings and the reduction in diesel emissions, there is the reduced hours on the truck engine.

"For a truck with a preventative maintenance schedule of 10,000 miles between servicing, the addition of an APU can reduce actual hours on the engine by over 38 percent," Tolstedt says. "This can translate into an additional 3,800 miles of operation on the truck engine between servicing. Over the course of a year, the owner can save $550 on engine preventative maintenance alone."

There is also the savings from truckers not incurring fines for violating the ever-spreading anti-idling laws, says Lande of Carrier Transicold. Plus, units like the company's ComfortPro APU "can significantly help to reduce wear and tear on the truck engine and allow for extended maintenance intervals, which also results in a savings."

He cites oil changes as an example, using a truck that idles roughly 50 percent of the time, is driven 120,000 miles annually and has the oil changed at a typical 20,000-mile interval. "That truck will require six to seven oil changes yearly at a cost exceeding $1,100," he says. "Eliminate the idling and you could cut the need and cost for engine oil changes by nearly half."

Another factor is engine life. "Engine rebuilds are typically done at 800,000 miles," observes Lande. "At that point, a typical engine with roughly 50 percent idle time will have about 32,000 operating hours - driving and idling combined. At $15,000 for a typical engine rebuild, the cost per engine-hour is about $0.49, which can translate to more than $1,000 a year just for the idling hours.

"Holding down engine hours through idling reduction generally extends the life of the engine, allowing a longer trade cycle and a higher resale value," he goes on. "Consider two trucks, each driven 650,000 miles. The one without an APU racked up 24,000 engine hours, while the other accrued only 12,000 engine hours because an APU was used during idling situations.

"Everything else being equal," says Lande, "it's clear which one would likely have the higher resale value."

It bears mentioning that auxiliary heating systems are not just for heating truck cabs and sleepers. There are units available to protect temperature-sensitive cargo from cold damage as well.