Most US RVs cool well with an 11,000, 13,500, or 15,000 BTU/h rooftop air conditioner, chosen by heat load rather than length.
Pick the biggest unit and you can end up with a camper that feels clammy, cycles on and off every few minutes, and strains a 30-amp campsite hookup. Pick too small and the coach never reaches the thermostat setting on a 100°F afternoon in Arizona. The working number is heat load, and the three capacities above cover nearly every towable and motorhome on US roads.
Camper AC Sizing Basics: How Many BTU Does an RV Need?
There is no official square-footage-to-BTU chart for RVs. Dometic publishes product capacities but no universal sizing table, so the honest method is matching capacity to the coach’s actual heat load.
Start with the conditioned floor area, then adjust for what the square footage hides. Two 28-foot trailers can need different units if one has dual-pane windows, a light-colored roof, and good insulation while the other has single-pane glass, a dark roof, and slide-outs baking in full sun. Ceiling height, occupancy, and the outdoor temperatures you actually camp in all move the answer.
- Smaller units run longer and pull more moisture out of the air. That longer run time is why a slightly smaller unit can feel better than an oversized one.
- Oversizing cuts dehumidification. A unit that blasts cold air for four minutes and shuts off leaves humidity behind, and short cycling wears the compressor.
- Multiple zones change the math. A 40-foot coach with a bedroom and a living area often wants two units rather than one large one.
| Dometic FreshJet Model | Capacity & Cooling Draw | Listed Price |
|---|---|---|
| FreshJet 5 Mechanical High Efficiency (FJX5357MHE) | ~11,000 BTU/h, 8.56–13.9 A | $1,187.49 |
| FreshJet 5 Mechanical 13.5K (9620015930) | 13,500 BTU/h | $1,346.99 |
| FreshJet 5 Mechanical 15K (FJX5557M) | 15,000 BTU/h, 12.66–19.73 A | $1,449.99 |
| FreshJet 5 Electronic 15K with heat pump | 15,000 BTU/h plus heat pump | $1,864.99 |
| FreshJet 3 Mechanical 15K (R32) | 15,000 BTU/h | $1,059.99 |
| FreshJet 3 Mechanical 13.5K (R410A) | 13,500 BTU/h | $899.99 |
Prices are Dometic’s listed US prices and exclude installation, controls, air-distribution boxes, shipping, and tax. If you’d rather compare specific models side by side before committing, this roundup of the best camper AC units for RV cooling walks through tested picks.
What Your RV’s Electrical System Can Actually Run
A 15,000 BTU/h mechanical unit is not a drop-in upgrade for an 11,000 BTU/h unit. The electrical and physical differences decide whether the swap works at all.
The FreshJet 5 High Efficiency model draws 8.56 A to 13.9 A — meaningfully less, which matters on a 30-amp hookup or a small generator.
Check your shore-power rating, generator or inverter capacity, startup surge, and branch-circuit protection before buying. Startup demand is the piece most people miss: a unit that runs fine can still trip a breaker the moment the compressor kicks on. FreshJet 5 units are low-profile, with a 10.5-inch installed fit height, and Dometic describes them as direct replacements for Penguin II models — but compatibility still has to be confirmed by model, control system, roof opening, mounting arrangement, and wiring.
Installation Details That Decide Compatibility
Refrigerant type, air distribution, and controls each break a swap that looked fine on paper.
Refrigerant type must match your replacement and service requirements — an R410A system is not automatically replaceable with an R32 system, and mixing them up is a service problem, not a paperwork one.
For non-ducted installation, Dometic states an air-distribution box is required. For ducted installation, a return-air grille and control kit are required, and these may be sold separately. Buying the unit alone and discovering the air box is missing is a common and expensive mistake. Roof sealing, electrical work, refrigerant service, and structural installation should follow the manufacturer’s instructions and applicable US electrical codes.
One more gate: choosing by RV length alone ignores insulation, glazing, climate, and solar gain — the factors that actually determine whether 13,500 or 15,000 BTU/h is right. Dometic’s published installation requirements apply to every model, and skipping them voids both the fit and the warranty.
Common Questions
Does a bigger BTU rating always cool an RV better?
No. An oversized unit cools the air quickly and shuts off before it removes much humidity, leaving the coach feeling damp, and the repeated short cycling adds compressor wear. A properly sized unit that runs longer usually produces a more comfortable result. Match capacity to heat load rather than defaulting to the largest available option.
Can I replace a 13,500 BTU/h unit with a 15,000 BTU/h model?
Sometimes, but not automatically. The two are not interchangeable despite the modest capacity gap. Current draw, controls, dimensions, and compatibility differ between them. Verify your electrical supply, roof opening, mounting arrangement, and control system against the specific replacement model’s listed requirements before ordering.
Why do ducted and non-ducted installations need different parts?
Dometic requires an air-distribution box for non-ducted installation, while ducted setups require a return-air grille and control kit instead. These parts may be sold separately from the unit itself. Ordering the air conditioner without confirming which distribution style your RV uses is one of the most common installation delays.
Sources
- Dometic. “Dometic FreshJet 5 Series Mechanical 15K” Lists 15K electrical draw, weight, roof cutout, R32 refrigerant, and installation requirements.
- Dometic. “RV Air Conditioners” Source for FreshJet model capacities, cooling current, and listed US prices.