By Norman Ford · Updated October 2026
Truck APU: what it is, types, and whether it pays
Long haul drivers rest in the truck, and the sleeper needs heat in winter and cooling in summer. Idling the main engine for 8 or 10 hours to do that burns fuel, adds engine hours and is restricted in many places. An APU does the same job far more efficiently. Whether it is worth buying depends on how you run.
Inside a truck APU
Tap each part to see what it does and what to maintain.
Tap a numbered balloon for the part's job, check and spec.
| ITEM | PART | WHAT IT DOES | CHECK |
|---|---|---|---|
| 1 | Power source | A small diesel engine and generator on a diesel APU, or a battery bank on a battery electric unit. | Diesel units: oil, filters and belts on the maker's schedule. Battery units: battery health and connections. |
| 2 | Climate unit | Heats and cools the sleeper. Often a heat pump or a separate air conditioner and fuel-fired heater. | Clean filters and condenser coils; check refrigerant performance at service. |
| 3 | Charging and alternator | Keeps the truck's starting batteries charged on diesel units; recharges the APU bank on electric units. | Charging voltage and battery condition. |
| 4 | Controls and thermostat | Lets the driver set temperature and run times; many units protect starting batteries automatically. | Low voltage cut-off settings and fault codes. |
| 5 | Mounting and exhaust | Diesel units mount on the frame rail with their own exhaust, often routed through the truck's aftertreatment or a filter. | Mount bolts, exhaust leaks and vibration damage. |
Diesel APU vs battery electric
Diesel APUs use a small diesel engine to run a generator and climate system, drawing fuel from the truck's tanks. They can run as long as there is fuel, handle extreme heat and cold well, and keep the truck's batteries charged. They add weight and need their own engine maintenance, and they make some noise and emissions.
Battery electric APUs store energy in a battery bank charged by the truck's alternator while driving, sometimes with solar panels or shore power. They run quietly with no fuel use while parked. Run time is limited by battery capacity and battery age (see how long a truck battery lasts), so very hot or cold nights and short driving days can leave the bank short. Our guide to the electric APU covers them in detail.
Both kinds depend on a healthy electrical system. Our truck battery guide covers battery types and checks.
| Factor | Diesel APU | Battery electric |
|---|---|---|
| Fuel while parked | Small amount | None |
| Run time | As long as there is fuel | Limited by battery capacity |
| Noise | Low engine noise | Quiet |
| Maintenance | Engine service: oil, filters, belts | Batteries, connections, climate system |
| Extreme weather | Handles long hot or cold nights | Can run short on very long or extreme nights |
| Weight | Added unit and mounting | Added batteries |
Why owners buy APUs
- Fuel. A heavy truck engine at idle is commonly estimated to burn around 0.8 gallons an hour. Over many hours a year, that adds up to thousands of dollars.
- Engine hours. Idling adds engine hours without miles, bringing hour-based service intervals sooner and adding wear.
- Rules. Many states and cities limit idling for heavy trucks, with exceptions that vary by place.
- Comfort and rest. Steady climate control without the noise and vibration of the main engine helps drivers sleep.
Weight exemption
An APU adds weight, which reduces payload. Federal law allows states to exempt the weight of idle reduction technology from vehicle weight limits up to a set amount, raised to 550 pounds. States apply the exemption differently, and some require proof that the unit works. Check the rules in each state you run.
Source: 23 CFR 658.17 (idle reduction weight exemption), checked October 2026
Cost and payback
APU prices depend on the type, brand and installation, and battery systems vary widely with battery capacity. The payback depends mostly on how many idle hours the unit replaces and the price of diesel. Our guide to semi truck APU cost covers price ranges and running costs, and the APU ROI and payback calculator works out your payback period from your own numbers.
A truck that idles many hours a night for most of the year pays off an APU much faster than one that is home most nights.
APU maintenance
- Diesel units: oil and filter changes, fuel filters, belts and coolant on the maker's schedule, plus the climate system.
- Battery units: battery health checks, clean connections, and the charging system.
- Both: clean cabin and condenser filters, check the thermostat and controls, and keep mounting hardware tight.
An APU that is not maintained fails on the hottest or coldest night of the year. Add its service to your PM schedule.
Which trucks benefit most
APUs make most sense on sleeper trucks that spend many nights on the road. Day cabs and trucks that are home every night rarely need one. For the truck classes and configurations where APUs are common, see our guide to the class 8 truck.
Choosing an APU
Before buying, answer a few questions about how you run:
- How many nights a year are you out? A truck that is home most nights rarely recovers the cost.
- Where do you run? Very hot or very cold regions put more demand on the climate system and favor units with longer run times.
- What do you power? A refrigerator, microwave, TV and laptops add electrical load on top of heating and cooling.
- How long will you keep the truck? The longer you keep it, the more time the APU has to pay for itself.
- Who services it? Check that dealers or shops in your area work on the brand.
Installation and warranty
APUs are installed on the frame rail, wired into the truck's electrical system and, on diesel units, plumbed into the fuel tanks. A poor installation causes electrical faults, fuel leaks and vibration damage. Use an installer experienced with your truck model. Check how the installation affects the truck's own warranty, and keep the installation paperwork. On diesel APUs, also check how the exhaust is handled; some states require diesel APUs on newer trucks to have their exhaust filtered.
Other ways to cut idling
An APU is not the only option. Some drivers use a fuel-fired heater for winter nights, which burns very little fuel. Insulated curtains, window covers and good bedding reduce how much heating and cooling the sleeper needs. Truck stops in some areas offer electrified parking spaces that supply power and climate control. Combining these with careful planning of where you stop can reduce idling even without a full APU.
Resale and the used truck market
A working APU can make a used sleeper truck easier to sell, especially to long haul buyers and in states with idling limits. A broken one can hurt, because the buyer prices in the repair. Keep service records for the APU along with the truck's.
APU and the truck's own batteries
Many diesel APUs also charge the truck's starting batteries while they run, which helps prevent a no-start after a long night. Battery electric units do the opposite: they draw from their own bank and rely on the truck's alternator to recharge it while driving. Either way, the APU and the starting system interact, so test both battery banks at each service and keep the low voltage protection set so the truck can always start.
Where we fit
We are a dispatch desk, not an equipment seller. We receive nothing from APU makers. We dispatch 26 ft box trucks and larger and plan loads around your rest and home time. Learn more about our dispatch service.