RV & Camper AC Sizing: How Many BTUs Does Your Rig Need?
Key Takeaway
Most RVs up to 25 feet need a 13,500 BTU rooftop unit; Class A motorhomes over 32 feet typically require two units totaling 28,000–30,000 BTU.
Editor's Picks
Top-Rated Cooling Units for US Homes
Matched to your calculated BTU range. Vetted for reliability, efficiency, and real-world performance.
Prices shown are estimates. We may earn a commission from Amazon links at no extra cost to you.
Expert Analysis
Shore Power Limits & Metal Skin Heat Gain: The RV Cooling Equation
RV cooling presents a unique combination of challenges not found in any fixed structure: a metal skin with minimal insulation, a roof exposed to direct solar gain, a small interior volume, and severe electrical power constraints.
An RV's aluminum or fiberglass skin typically provides R-5 to R-7 of total insulation — far below the R-13 minimum recommended for residential walls. On a 95°F day with full sun on the roof, interior temperatures can rise to 130°F+ within 30 minutes of parking in direct sun. The thermal envelope is also compromised by slide-out seals, window frames, and door gaskets that degrade with road vibration and UV exposure.
Electrical constraints shape equipment selection as much as BTU requirements. A 30-amp shore power pedestal provides 3,600W total — enough for one 13,500 BTU unit (1,500W running) plus limited other loads. A 15,000 BTU unit draws approximately 1,800W running and 3,500W+ at startup, potentially tripping a 20-amp pedestal breaker before the compressor even reaches steady state.
For boondocking or generator use, soft-start technology is essential. Standard AC compressor starting current is 45–65 amps; soft-start capacitor kits reduce this to 12–18 amps, allowing operation on a 2,000W portable generator.
Buying Guide
Soft-Start Technology: Non-Negotiable for Generator & 30-Amp Camping
Must-Have Features
Soft-Start Technology
A soft-start capacitor kit (MicroAir EasyStart or equivalent) reduces AC compressor starting current by 65–70%, from 45–65 amps down to 12–18 amps. This is essential for generator use and allows the AC to operate on 20-amp pedestals or a 2,000W portable generator — dramatically expanding your camping options.
Low-Profile Rooftop Design
RV rooftop AC units must clear overhead bridges and low-clearance campground facilities. Low-profile units typically sit 8–10 inches above the roofline; standard units add 14–16 inches. Verify height clearance against known obstacles on your routes before selecting a unit.
High Energy Efficiency Ratio (EER)
When running on a generator, every watt of AC inefficiency is a watt the generator must produce — burning fuel and adding noise. An RV unit with EER 11+ versus a baseline EER 8 unit reduces generator fuel consumption by approximately 27% for the same BTU output over a camping weekend.
Pro Tip
Park with the RV's longest side facing north when possible, and deploy an awning on any south or west-facing windows before leaving for activities. An RV parked in full afternoon sun with unshaded windows can reach interior temperatures of 140°F+ within an hour — a heat load your AC physically cannot overcome. Shade the roof and windows first; the AC manages the residual load. A reflective roof coating applied to an aluminum roof reduces roof surface temperature by 20–30°F, reducing the total BTU load by 10–15%.
Common Mistake
Don't Run Two High-BTU Units on a 30-Amp Service
A 30-amp shore power pedestal provides 3,600W total. Two 13,500 BTU units draw approximately 3,000W running — leaving only 600W for everything else. At startup, each unit can spike to 2,500–3,500W, and if both attempt to start simultaneously, you will trip the pedestal breaker immediately. If your rig requires dual AC units, ensure your campsite provides a 50-amp service (6,000W), use a load-management system that staggers compressor starts, and install soft-start kits on both units.
Expert Advice
“RV cooling is constrained from both ends: extreme heat gain through poorly insulated aluminum walls and roof, and strict power limits from a 30-amp shore power pedestal or generator. A 15,000 BTU rooftop unit draws roughly 12–14 amps at startup — on a 20-amp circuit, that leaves almost nothing for other appliances. Always verify your campsite's electrical service before selecting unit capacity.”
Industry Terminology
Terms You Should Know
- Soft-start capacitor
- Electronic module that reduces AC compressor starting current from 45–65A down to 12–18A, enabling generator operation.
- 30-amp service
- Standard RV shore power pedestal providing 3,600W total; limits which AC units can operate simultaneously.
- EER (Energy Efficiency Ratio)
- BTU/h of cooling per watt of electricity; higher EER means less generator fuel burned for the same cooling output.
- Boondocking
- Camping without shore power; relies on generator or battery/solar — soft-start and high EER are critical for viability.
- Reflective roof coating
- Elastomeric coating applied to an RV's roof, reducing surface temperature by 20–30°F and total BTU load by 10–15%.
- Low-profile rooftop unit
- RV AC design that sits 8–10 inches above the roofline vs. 14–16 inches for standard units; required for low-clearance routes.
- RV envelope R-value
- Total thermal resistance of RV walls; typically R-5 to R-7, far below residential R-13+, driving higher per-sq-ft BTU needs.
Quick Reference
BTU Chart by Room Size
| Room Size | BTU Required | Tonnage |
|---|---|---|
| 100 – 150 sq ft | 5,000 BTU | 0.4 ton |
| 150 – 250 sq ft | 6,000 BTU | 0.5 ton |
| 250 – 400 sq ftBest Seller | 8,000 BTU | 0.7 ton |
| 400 – 550 sq ft | 10,000 BTU | 0.8 ton |
| 550 – 700 sq ftMost Popular | 12,000 BTU | 1.0 ton |
| 700 – 1,000 sq ft | 14,000 BTU | 1.2 ton |
| 1,000 – 1,400 sq ft | 18,000 BTU | 1.5 ton |
| 1,400 – 2,000 sq ft | 24,000 BTU | 2.0 ton |
| 2,000 – 2,500 sq ft | 30,000 BTU | 2.5 ton |
Based on ASHRAE Standard 183 guidelines. Assumes 8 ft ceilings, average insulation, and moderate sun exposure. Add 10% for kitchens; subtract 10% for heavily shaded rooms.
Keep Exploring
Discover More Sizing Guides
Each guide uses room-specific load factors for a more accurate result.