Living out on the road can become grueling. Over the road truckers will do just about anything to be as comfortable as possible while out on the road. That’s where APU come in. An APU can help drivers stay comfortable while helping keep fuel consumption at a minimum.  In this blog, we’ll explore what an APU is on a truck and how it works.

What Is an APU?

An auxiliary power unit, also known as APU, is a small yet efficient motor that allows drivers to use their HVAC without continuously using their truck’s fuel. While homes have power generators, trucks have APUs that work as inverters for their heat & AC system.


Example of an APU. (Source)

As previously stated, an APU allows drivers to use their HVAC while resting without idling the motor. This way, they can preserve fuel through their trips. Aside from keeping the HVAC functional, APUs can also allow drivers to run interior appliances like micorwaves and refrigerators while parked. 

What Are the Benefits of APUs?

APUs have several benefits, including reduced fuel consumption, lower emissions, and improved driver comfort and safety. To explore these benefits in more detail, let’s look at each one closely:

Fuel Economy

According to the Department of Energy, heavy-duty trucks such as those Class 7 and above consume about 0.8 gallons of fuel/hour when placed on idle mode. A typical vocational hauling trip requires truck drivers to leave their trucks idle for up to 10 hours, which converts into 8 gallons of fuel lost while drivers are resting. With APUs, truck drivers will save gallons of fuel and prevent engine damage caused by continuous idling.


Contrary to popular belief, idling can be as dangerous as a moving truck to the environment. According to North Carolina Environmental Quality, idling releases harmful chemicals, gasses, and particles called “soot,” significantly contributing to air pollution. Every gallon of gas burned produces more than 20 lbs. of greenhouse gasses, contributing to regional haze, the deterioration of the ozone, and global climate change.

While some APUs still use fuel, they help heavy-duty trucks produce less carbon footprint compared to continuous idling. 


Sample of a truck ready for APU

Protection Against Anti-Idling Law

Due to the harmful effects of idling on the environment and public health, numerous major cities worldwide have also implemented anti-idling policies. In New York City, being idle for 3 minutes is considered illegal, and vehicle owners would be fined $250. The restrictions, fines, and penalties vary from city to city. So, to reduce inconvenience in your trucking services, it’s best to have an APU ready. 

Increased Driving Productivity

A driver can only remain efficient and productive with proper rest–this is one of the major reasons why sleeper cabs were introduced to the market. While utility trucks provide drivers plenty of space to rest, harsh weather conditions, especially in the countryside, can be detrimental to the riding experience of drivers. Having an APU helps ensure that drivers can safely and productively hit their hauling targets whenever and wherever they may be assigned.

How Does an APU Work?

To understand how an APU works, it’s essential to look at its categories and installation process. 

Kinds of APUs

As of this writing, various APUs are available on the market today. However, they can be generally classified as Combustion APUs and Electric APUs.

Combustion APUs

Combustion APUs are the most common kind of APUs for vocational hauling. These kinds use fuel to generate electricity for a sleeper cab. Most combustion APUs run on diesel, but some run on natural gas or propane. 

Compared to electric APUs, combustion APUs are more economical and efficient, as they generate enough electricity to warm up or cool down large sleeper cabs. They also have enough power to run other temperature-based appliances, such as microwaves or compact fridges. However, combustion APUs are very high maintenance, as they require frequent oil and fuel filter changes, among other preventive maintenance.

Electric APUs

Electric APUs are mostly used for regional hauling and delivery services, as they can only generate electricity for 12 hours of use. This consumption rate can be further decreased depending on the HVAC size of your cab.

A standard electric APU can be fully charged for approximately 10 hours by plugging it into a truck engine or electric outlet. While it may be less efficient than a combustion APU, an electric APU requires less maintenance as it works like a heavy-duty battery for your truck.


APU for trucks, ready for installation. (Source)

Using Your APUs

APU installation and usage vary depending on the unit of your truck. In most cases, a combustion APU is usually mounted on the frame rail of the truck, behind the fuel tank, and in front of the first axle. Your APU will be connected to the truck’s fuel supply, compressor, alternator, and generator, so you can easily switch from fuel to your APU when powering your HVAC.

Aside from installing the unit, your APU should also be programmed, depending on your truck model. The APU should be properly connected to your ignition with an integration switch, as this would allow the unit to function when the engine is turned off. It’s also essential to sync your APU to your engine, which will automatically charge when running low on power.

An additional set of temperature dials would also be installed when connecting your APU to your HVAC unit. These controls would be different from your standard auxiliary controls. 

Using your APU can be pretty tricky, especially if it’s not installed properly. A single connection mistake between your APU, engine, and compressor may cause damage to your truck’s overall power use. We highly recommend getting professional installation services to ensure it’s properly and safely installed.

What to Look for in a Good APU

There are major factors that you should consider when getting a good APU, including the truck model, driving routines, features, maintenance costs, and materials used. To learn more about them, let’s discuss each factor:

1. Truck Model

In most cases, the truck model would determine the APU you could use. Your APU’s size, capacity, features, installation techniques, and programming process should be based on your truck unit. While there are many ways to configure your APU based on your liking, you must ensure its full compatibility with your truck unit.

2. Driving Routines

As mentioned a while ago, APUs have various power generation capacities. To determine which APU you’d need, it’s essential that you determine your driving routine. This includes identifying your resting time, the length of your trip, the weather conditions at your usual destination, and more. Having a low-capacity APU for long hauls may be useless. At the same time, having a high-capacity APU when you’re only used to short drives can cost you a hefty amount in operational and maintenance costs.

3. Features and Functionalities

Most APUs can be fully connected to a truck’s HVAC unit, so it can warm up and cool down the cab when needed. However, some brands of APUs only have cooling features, as warming up a cab requires more fuel and electricity. These APUs are perfect for trucks that mostly travel to warm destinations or have short-term rides. Identifying the features and functionalities you need will allow you to maximize the benefits of your APU.

4. Maintenance and Installation Costs

Your APU will require regular and expensive maintenance procedures. Additionally, APU installation can be pretty costly, too. 

Most business owners and truck drivers validate that an APU is a worthy investment for hauling services. However, it’s still imperative to account for these operational costs when getting an APU.

The APU body/shell is typcially one of the parts that go quickly, particular for drivers that drive in the salt belt. These steel shells will rust out, at the minimum, they become an eyesoar, and it’s worst a road hazard that exposes your APUs motor to the elements.  That’s why Shoreline Truck Parts has started building stainless steel APU parts.


Premium APU steel cover

5. Premium Materials

To ensure that you can fully enjoy the benefits of your APU, you must find one made of premium materials. This doesn’t just include the motor itself but also the housing that protects your APU. If you want to proactively beat the rust or you need to replace your rusty APU shell, check out our stainless steel APU cover/panels. 

Prioritize Your Driving Experience Today with a Functional APU

No truck can be productive and profitable without a comfortable driver. And having an excellent APU will ensure that you get to have enough rest to fulfill your trucking services without sacrificing that much money due to continuous fuel use.

My cart
🎁 Only $50.00 away from free shipping to
Your cart is empty.

Looks like you haven't made a choice yet.