If you’re out on the road running long hauls, you already know how valuable comfort and fuel savings are during your rest breaks. That’s where an APU – auxiliary power unit –comes in. An APU powers your truck’s air conditioning, heat, and in‑cab electronics without running the main engine. APUs are becoming increasingly essential as anti‑idling rules tighten across the country and fleets seek ways to cut fuel costs.
What an APU Does
An APU keeps everything running in your sleeper when the truck is parked – HVAC, appliance outlets, lights, and more – all with the main engine turned off. This means a quieter truck, less fuel burned, and much less wear and tear on your engine. APUs are considered a leading Idling Reduction Technology (IRT) by the EPA because they help drivers rest comfortably while reducing emissions and noise.
Diesel/Combustion APUs
Diesel APUs are the most common, powering HVAC and appliances for long periods with minimal fuel use.
They do need regular maintenance, such as oil and filter changes, just like truck engines, to keep them running strong. You’ll see diesel options from familiar brands like Thermo King, Carrier Transicold, and Green APU, which are all well‑known names in the APU market.
Electric/Battery APUs
These have made huge leaps thanks to lithium iron phosphate battery technology. Newer electric APUs can now power your HVAC for a full 10‑hour rest period, even in tougher climates.
Electric APUs are silent, produce zero emissions, and require almost no maintenance. They charge while you’re driving via the alternator, and many support shore power or solar add‑ons. Cooling performance typically ranges from 6,000–12,000 BTUs, which is solid for sleeper‑cab comfort.
Benefits of Using an APU
Fuel Savings
Main engine idling burns significant fuel. Diesel APUs use much less, and battery APUs save even more. Annual savings can be substantial.
Reduced Engine Wear
Every hour of engine idling adds maintenance costs and reduces engine life. APUs help reduce unnecessary engine hours.
Anti‑Idling Compliance
Most states have idling rules, and California caps idling at five minutes for heavy‑duty diesel vehicles. The 2025 ATRI compendium shows updated state‑by‑state rules, making APUs even more important for avoiding fines.
Driver Comfort
APUs ensure consistent air conditioning or heat without engine vibration or noise, especially with newer lithium systems that are almost silent.
Environmental Benefits
Semi-truck APUs cut emissions and meet EPA recommendations for reducing long-duration idling.
Cost & ROI: When an APU Pays for Itself
Between diesel savings and reduced engine wear, many fleets see annual fuel savings of $3,500–$6,000, depending on hours idled.
Since diesel APUs burn only a fraction of the fuel that idling consumes – and battery APUs burn none – most drivers break even within 1–2 years. This is especially true if you spend nights in your truck, run regional routes with frequent breaks, or operate in states with strict idling laws.
APU Weight Exemption Rules
Under the federal MAP‑21 legislation, trucks with APUs get a 550‑lb weight exemption to help offset the added equipment weight.
But state rules vary:
- Some states fully honor the 550‑lb exemption (e.g., Wisconsin, Virginia).
- Others, like California, don’t officially recognize the exemption but may allow it at the officer’s discretion.
- Drivers should carry documentation showing the APU’s weight and specs in case of roadside inspections.
Things to Consider Before Buying an APU
Truck compatibility
Not all units fit all trucks; check frame space and mounting options.
Power needs
Think about HVAC load, electronics, and overnight appliance use.
Battery vs. diesel
Choose based on climate, duty cycle, and fuel-savings goals.
Installation space
Diesel APUs require more room than battery systems.
Maintenance preference
Diesel requires regular upkeep; lithium systems require very little.
The Value of APU for Trucks
An APU is one of the most valuable upgrades you can add to a truck. Whether you go diesel or electric, you’ll save fuel, reduce engine wear, stay compliant with idling laws, and get a quieter, more comfortable break. With diesel fuel prices always fluctuating, an APU is a solid long‑term investment in your comfort and your bottom line.
How the TCS Fuel Card + an APU = Big Savings
If you want to stretch those APU savings even further, the TCS Fuel Card helps you save big on diesel fuel right at the pump at more than 2,300 in-network discount locations, such as TA®, Petro Stopping Centers®, TA Express®, 7 FLEET Diesel Network – 7-ELEVEN®, Speedway®, Stripes, AMBEST®, Maverik, and more. The TCS Fuel Card is a smart way to keep operating costs in check while you’re out there doing the hard hauling work.
All truckers can save money at the diesel pump, with or without an APU. That’s what the TCS Fuel Card offers for owner-operators, small trucking companies, and large fleets at more than 2,300 in-network discount locations across the country. Are you ready to save on diesel? We are ready for you! Apply for the TCS Fuel Card today!
