APU ROI and payback calculator

This APU ROI and payback calculator returns the yearly savings from replacing engine idling with an auxiliary power unit, the payback period in months and the five-year result after the purchase price.

Idling a big diesel engine for heat or air conditioning is one of the most expensive ways to keep a sleeper comfortable. An APU does the same job with far less fuel, but it costs money up front and needs its own upkeep. Whether it pays off depends on how much you idle.

How it works

• Idle fuel avoided = idle hours replaced per year x engine idle burn x diesel price
• APU fuel = the same hours x APU burn x diesel price (zero for a battery electric unit)
• Net yearly savings = idle fuel avoided + optional engine wear avoided - APU fuel - APU upkeep
• Payback = APU price / net yearly savings x 12 months
• Five-year result = net yearly savings x 5 - APU price

The default idle burn is a commonly cited estimate, and the APU price is an EXAMPLE. Use your quote and your truck's numbers.

A worked example

An owner idles about 1,800 hours a year for heat and cooling. The engine burns about 0.8 gallons an hour at idle and diesel costs $3.90. A diesel APU quoted at $12,000 installed burns about 0.2 gallons an hour and costs about $600 a year to service.

• Idle fuel avoided: 1,800 x 0.8 x $3.90 = $5,616
• APU fuel: 1,800 x 0.2 x $3.90 = $1,404
• Net yearly savings: $5,616 - $1,404 - $600 = $3,612
• Payback: about 40 months
• Five years: $18,060 - $12,000 = about $6,060 ahead

At 900 idle hours a year, the same APU would take about twice as long to pay off. Hours are everything.

What changes the answer

• Idle hours. Count real hours: overnight, waiting at docks and during breaks. The idle cost calculator helps estimate them.
• Diesel price. Higher prices shorten payback.
• APU type. Battery electric units burn no fuel but have limits on run time; diesel units run longer but need engine service. Our guides to the electric APU and the truck APU compare them.
• Upkeep. Filters, belts, oil and repairs for a diesel unit; batteries and charging for an electric one.
• Engine wear. Idle hours count toward hour-based service intervals. If you value that wear, add it in the optional line.

Idling rules

Some states and cities limit how long a truck may idle, and some require an APU or another approved system to run climate control while parked. California, for example, limits idling for heavy diesel vehicles in most situations. If you run in areas with idling limits, an APU may be less of a choice and more of a requirement. Check the rules where you park.

Counting your idle hours

Most estimates of APU payback go wrong on idle hours. Guesses tend to be low. Many engines record idle time, and a shop or your engine maker's software can read it. If you cannot get the data, keep a simple log for two weeks: when you start idling, when you stop, and why. Overnight climate control is usually the big number, but dock waits and breaks add up too. Multiply the two-week total by the weeks you work in a year.

Resale and financing

An APU can add value when you sell the truck, especially in markets with idling limits, though how much varies. If you finance the unit, include the interest in the price, or the payback will look faster than it is.

When an APU may not pay

If the truck is home most nights, idles little, or you plan to sell it within a year or two, payback may never arrive. Leasing, used units or a smaller battery system may make more sense. Run the numbers for the time you expect to keep the truck.

Fitting it into the bigger picture

An APU changes your fuel cost, your maintenance and the truck's resale value. To see what each load leaves after costs, the load profitability calculator brings fuel, wear and trip costs together.

Where we fit

We are a dispatch desk, not an equipment seller. We find and negotiate loads for 26 ft box trucks and larger, you say yes, counter or no, and the broker sends the rate confirmation to you to sign. Our page for owner-operators explains how we work with single trucks.