Idling feels free at 2 a.m. — it isn't. Enter how much you idle and at what diesel price to see the cost per day and per year, the gallons you're burning, and whether an APU pays for itself.
A truck idling its main engine burns about 0.8 gallons an hour — about $3.66/hour or $7,300+/year at $4.57/gal diesel (2026); a diesel APU (~0.25 gal/hr) cuts that roughly 75% and usually pays back in 1.5–3 years above ~1,000 idle hours a year.
Source: DOE/Argonne National Laboratory idle-burn data; U.S. EIA diesel price (~$4.57/gal, week of July 6, 2026). Updated July 2026.
Fuel only — this doesn't count the extra maintenance and engine-hour wear idling adds (often another $1,000–$3,000/yr), or idling-law fines. Adding paid miles shows what idling adds to your cost per mile.
The main engine burns roughly 0.8 gallons an hour at idle — DOE/Argonne and fleet data put it between 0.6 and 1.0 gal/hr depending on A/C, heat, and accessory load. At a 2026 diesel price near $4.57/gal (EIA, week of July 6, 2026), every idle hour is about $3.66 in fuel. Idle 8 hours a night, five nights a week, and you'll burn around 1,600 gallons — roughly $7,300 a year in fuel alone. Add maintenance and the engine-hour wear (idling is often cited as equal to about 200,000 extra miles), and industry estimates land at $4,000–$7,000+ per truck per year.
Annual fuel cost of idling the main engine at 0.8 gal/hr, 5 nights/week, 50 weeks/year — by idle hours per night and diesel price:
| Idle hrs/night | $4.50/gal | $5.35/gal | $6.50/gal |
|---|---|---|---|
| 4 hrs | $3,600 | $4,280 | $5,200 |
| 6 hrs | $5,400 | $6,420 | $7,800 |
| 8 hrs | $7,200 | $8,560 | $10,400 |
| 10 hrs | $9,000 | $10,700 | $13,000 |
A diesel APU (~0.25 gal/hr) cuts the fuel side ~75%; a bunk heater cuts overnight heat idling for far less. Both are usually exempt from idling laws.
Idling the main engine is the most expensive way to keep the cab livable. Here's how the common alternatives stack up on fuel — per 10-hour night at $4.57/gal diesel, and per year at 1,000 idle hours:
| Option | Fuel use | Cost / 10-hr night | Fuel cost / yr (1,000 hrs) |
|---|---|---|---|
| Idle main engine | ~0.8 gal/hr | ~$37 | ~$3,660 |
| Diesel APU | ~0.25 gal/hr | ~$11 | ~$1,145 |
| Battery-electric APU | 0 gal (charges while driving) | ~$0 fuel | ~$0 fuel* |
| Bunk heater (heat only) | ~0.05 gal/hr | ~$2 | ~$230 |
| Truck-stop shore power | plug-in, ~$1–2/hr | ~$10–20 | varies by stop |
*Battery-electric APUs burn no fuel but add battery replacement (~every 3–4 years) and a higher install price, and are capped by battery capacity on long, hot nights. Diesel APU: 0.25 gal/hr × 10 hrs × $4.57 ≈ $11/night. Planning estimates — your climate, HVAC load, and equipment move them.
About $3.66/hr at 0.8 gal/hr and $4.57 diesel. A full 10-hour break idling is ~$37 in fuel — every night.
Idling ~8 hrs a day, 5 nights a week burns roughly 1,600 gallons a year — about $7,300 at 2026 diesel. Counting maintenance and engine-hour wear, all-in estimates run $4,000–$7,000+ per truck per year.
Usually yes if you idle more than ~1,000 hrs/yr. At 0.25 gal/hr it saves several thousand dollars a year vs main-engine idle; with ~$8,500–$13,000 installed cost, payback is typically 1.5–3 years. Run your own numbers above.
Many states and cities cap idling (often 3–5 minutes when parked) with fines from the low hundreds into the thousands. APUs and bunk heaters are generally exempt.
For heat only, a diesel bunk heater burns ~0.05 gal/hr — about $2 a night — and is the cheapest fix. For heat and A/C, a diesel APU (~0.25 gal/hr) or a battery-electric APU pays back fastest if you idle heavily; truck-stop shore power works where it's offered. Idling the main engine is almost always the most expensive option per night.
Idle fuel burn (~0.8 gal/hr main engine, ~0.25 gal/hr APU) from DOE/Argonne National Laboratory and NACFE idle-reduction research; 2026 diesel price from the U.S. EIA (~$4.57/gal, week of July 6, 2026). All-in idle cost ($4,000–$7,000+/yr) and the ~200,000-mile engine-wear equivalence are industry estimates. Sources: Argonne idle-reduction research, NACFE diesel APUs, U.S. EIA. Fuel-only estimate for planning. Last updated July 2026. Built by TruckMargin.
Idle fuel is one line in your operating cost. See your full cost per mile, compare fuel-card savings and cost per mile by truck type, then check what's actually left after the load with the owner-operator take-home pay and factoring cost calculators.