The short answer
Most Class 8 sleepers need 2,000–2,400 W (approximately 6,800–8,200 BTU/h) of cooling. In hot climates, size up rather than down: an undersized unit runs continuously, never reaches temperature, and flattens the battery. Oversizing wastes capacity and money but is easier to live with.
Sizing a parking air conditioner is four measurements: cab volume, heat load, system voltage, battery capacity.
Step 1 — Measure your sleeping space
Volume = berth length × cab width × interior height.
| Sleeper berth | Typical volume |
| 40–52 in | ≈ 4.5–6.0 m³ |
| 72 in | ≈ 8.3 m³ |
| 80 in | ≈ 9.2 m³ |
An 80-inch sleeper is only about 11% larger than a 72-inch, so it rarely justifies a jump in cooling capacity.
Step 2 — Apply a heat-load factor
Cooling demand per cubic metre depends on climate and sun exposure:
| Condition | BTU/h per m³ |
| Moderate (below 32 °C / 90 °F) | 550–700 |
| Hot (35 °C+ / 95 °F+, direct sun) | 800–1,000 |
| Extreme (desert, high humidity, poor insulation) | 1,000–1,200 |
A 72-inch sleeper at 8.3 m³ in hot conditions needs roughly 6,600–8,300 BTU/h, which matches the 2,000–2,400 W band above. Extreme conditions push toward 10,000 BTU/h or more.
Step 3 — Confirm your system voltage
This is where most sizing mistakes happen.
- 12V — North American Class 8 tractors, light trucks, most RVs. Battery banks are wired in parallel.
- 24V — European and Chinese heavy trucks, most construction equipment. Two 12V batteries wired in series.
Check the battery wiring to confirm. A 24V system draws half the current of a 12V system for the same cooling output, which means thinner wiring and less heat loss.
| System | Typical draw | 2,000–2,400 W class |
| 12V | ≈ 70 A at 850 W | 12V units |
| 24V | ≈ 35–42 A at 850–1,000 W | 24V units |
Step 4 — Size the battery bank
Running time = battery energy ÷ (unit draw × duty cycle). Allow for 50% depth of discharge (DoD) on lead-acid; 80% on lithium.
For a 10-hour rest period:
- 24V system: ≈ 417 Ah worst case, ≈ 292 Ah typical
- 12V system: ≈ 833 Ah worst case, ≈ 583 Ah typical
A 12V system needs twice the Ah of a 24V system for the same stored energy — halving the voltage doubles the current.
Choosing the format
| Type | Best for | Notes |
| Rooftop | Class 8 sleepers, fleet installs | Largest capacity, cleanest install, no cab floor space used |
| Split | Vans, day cabs, tight cabs | Condenser remote-mounted; more installation work |
| Portable | Occasional use, rentals | Lowest capacity, no permanent install |
What to check before buying
- Cooling capacity in W and BTU/h — verify both, as figures are sometimes quoted in only one unit.
- Voltage match — 12V and 24V units are not interchangeable.
- Refrigerant — R134a is being phased toward lower-GWP alternatives such as R454C and R32 under EU F-Gas rules and California CARB. Ask which refrigerant a unit uses and whether service is available locally.
- Current draw and wiring — confirm the alternator and cabling can carry the load.
Compliance: EPA SmartWay and DERA
The EPA's SmartWay programme maintains a Battery Air Conditioning Systems (BAC) category on its verified list of idle-reduction technologies for trucks. Note the scope: this list covers long-haul, Class 8 trucks equipped with sleeper cabs, plus school buses. Verified equipment must be able to provide idle-reduction service for no less than eight continuous hours.
Verified idle-reduction equipment is the reference point for anti-idling compliance programmes and for grants and rebates under the Diesel Emissions Reduction Act (DERA). Two points matter for buyers:
- For DERA eligibility, the technology must be specifically named on the EPA Verified Idle Reduction Technology List and specified for the vehicle application in the project. Confirm the exact make and model is listed before relying on funding.
- Battery Air Conditioning Systems and Fuel Operated Heaters are not categorised as APUs, and are therefore not subject to the APU restrictions that exclude equipment on 2007-or-newer model year vehicles.
The U.S. Department of Energy's Alternative Fuels Data Center uses the term "storage air conditioners" for the same class of equipment that EPA calls BAC. Argonne National Laboratory estimates that more than one million long-haul heavy-duty trucks idle during federally required rest periods every day — which is why this category exists.
FAQ
Can I run a parking AC all night on batteries? Yes, with a correctly sized bank. A 24V system needs roughly 292–417 Ah for a 10-hour rest period at 50% DoD; a 12V system needs roughly 583–833 Ah.
Will a parking AC void my truck warranty? Not when installed per the manufacturer's instructions. Rooftop units are self-contained and do not modify the engine or drivetrain.
Do I need a fuel-operated heater too? BAC systems typically pair with a fuel-operated heater for cab heating. Heating from battery power alone is impractical at these capacities.
12V or 24V for a North American truck? Almost always 12V. Confirm by checking whether the batteries are wired in parallel (12V) or series (24V).
About Changzhou Holicen New Energy Technology Ltd.
Holicen manufactures electric parking air conditioners, fuel-operated heaters, compressors and vehicle refrigerators for 12V and 24V systems. Products are sold through Alibaba.com and hlskaac.com, with export support for distributors and fleet customers in high-temperature markets.
Media contact: [email：holicen@hlskaac.com]
Post time: Sep-24-2026