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RV Air Conditioner Size Calculator: Find the Right Rooftop AC BTU

Size your RV air conditioner from the rig's real heat load - walls, roof sun, air leakage, and occupants - then get matched to actual rooftop unit sizes with short-cycling protection and full power guidance for shore, generator, and battery use.

RV Air Conditioner Size Calculator

Heat-balance load calculation matched to real rooftop unit sizes

Your RV

RV type and size
ft (exterior)

Where & How You Camp

Camping conditions

Recommended RV AC Size

Interior Area:208 sq ft
Design Temp Difference:25°F
Walls / Roof / Windows:5,404 BTU
Sun Through Glass:2,984 BTU
Air Leakage:913 BTU
People & Appliances:1,500 BTU
Total Cooling Load:11,880 BTU/hr

Buy this configuration

13,500 BTU rooftop unit

Delivers ~12,690 BTU in your climate (rooftop units lose ~6% capacity in this heat)

A ductless (non-ducted) unit is fine for a rig this size.

Power Requirements

Running Draw
1,450W
~12.6A @ 115V
Startup Surge
55-70A
per unit, no soft start
Min. Generator
3,000W
without soft start
With Soft Start
2,200W
surge drops to 25-35A

One 13,500 BTU unit runs fine on a 30-amp hookup (~12.6A running), but watch total load - the microwave or water heater running at the same time can trip the pedestal.

Load model: steady-state heat balance (envelope conduction + solar gain + infiltration + internal gains) with RV-specific U-values, sol-air roof temperatures, hot-ambient capacity derating, and a short-cycling guard.

What Size RV AC Do I Need?

RV rooftop air conditioners come in three practical sizes: 11,000 BTU low-profile (vans and height-restricted rigs), 13,500 BTU (the standard for rigs up to about 27 feet), and 15,000 BTU (27-32 foot rigs and hot climates). Past 32 feet, you need two units- not because of BTUs, but because one ceiling vent can't push air the length of the rig.

Bigger is not safer: an oversized unit short-cycles, never dehumidifies, and dies early. The calculator above computes your rig's actual heat load and picks the smallest configuration that genuinely covers it.

RV AC Size by Rig Length (Quick Reference)Assumes standard build in full sun. Hot/desert climates push each row up one step - use the calculator for your exact case.
RV Length / TypeApprox. AreaRecommended AC
Camper van / truck camper (under 20 ft)< 150 sq ft11,000 BTU low-profile
Travel trailer / Class C, 20-27 ft150 - 300 sq ft13,500 BTU
Large trailer / small Class A, 27-32 ft300 - 380 sq ft15,000 BTU
5th wheel / Class A / toy hauler, 32-38 ft380 - 480 sq ft2 × 13,500 or 15,000 + 13,500 BTU
Big rig, 38+ ft480+ sq ft2 × 15,000 BTU (3 zones on 40+ ft)

How RV AC Sizing Actually Works

House calculators start from square footage because houses are insulated. An RV is a thin aluminum-and-foam box (R-4 to R-9 walls versus R-13+ in a house) with a roof that sits in direct sun all day - so our calculator computes a real heat balanceinstead: conduction through the walls, roof, windows, and floor at your climate's design temperature; a sol-air temperature bump on the roof of up to 35°F in full sun; solar radiation through the glass; air leakage (RVs leak 1-2 full air changes per hour); and the heat your people and appliances put out. A 10% pull-down allowance on top covers recovering a rig that heat-soaked all afternoon.

The result is matched to real rooftop sizes with one more correction most guides skip: rooftop units lose 6-12% of their rated capacity when it's 100°F+ outside - exactly when you need them most. That's why the calculator sometimes recommends 15,000 BTU in Phoenix for a rig that gets by on 13,500 in Michigan. All the U-values, sol-air temperatures, and derating factors are published in our methodology.

The Short-Cycling Trap: Why Bigger Fails Sooner

The most common RV AC mistake is putting a 15,000 BTU unit on a 22-foot trailer. It cools the small space so fast the thermostat clicks off within minutes, then back on, then off - short cycling. Each restart is the hardest moment of a compressor's life, so the unit accumulates thousands of extra starts per season and dies years early. Worse, an AC only dehumidifies while it runs; short cycles leave the rig cold but clammy. A correctly sized 13,500 runs long, steady cycles that wring the moisture out and spread wear over far fewer starts. This is a big part of why some factory units fail in 3-5 years while a properly matched unit runs for decades.

Power: 30-Amp, Generators, and Soft Starts

Sizing the AC is only half the buying decision - you also have to start it. A 13,500 BTU compressor surges 55-70 amps for a split second at startup (65-85A for a 15,000), which is what actually dictates generator size: roughly 3,000W for a 13,500 and 3,600W for a 15,000. A soft start module (like the MicroAir EasyStart) ramps the compressor up gradually and cuts that surge to 25-35 amps - suddenly a 2,200W inverter generator, or even a solar battery bank, can run the AC. If you boondock, budget for the soft start as part of the AC purchase.

On shore power: one AC runs fine on a 30-amp pedestal; two units require 50-amp service (or an energy-management system that alternates them). For battery-powered camping, the new inverter-driven variable-speed units are the game changer - they modulate output instead of slamming on and off, roughly halving average power draw.

Ducted vs. Ductless, and the $15 Fix Worth Trying First

If your rig has ceiling vents in multiple rooms, buy the ducted version of the unit so cold air reaches the bedroom; short single-room rigs are fine with a ductlessunit that dumps air straight down from the ceiling assembly. And before replacing a unit that's "weak and loud": pull the interior shroud and inspect the plenum. Factory installs routinely leave gaps that let cold supply air leak straight back into the hot return. Sealing the plenum with foil tape and adding a foam divider between the hot and cold sides is a $15 job that owners report boosts vent airflow by 40%+ and noticeably drops the noise - often the difference between "needs replacing" and "works like new."

Sizing a whole house instead? Use our main AC tonnage calculator, or the mobile home AC calculator for manufactured housing. For a room unit, see the window AC BTU calculator or portable AC calculator.

Frequently Asked Questions

What size air conditioner do I need for a 30-foot travel trailer?

A 30-foot travel trailer (roughly 240 sq ft) camped in full sun in a hot climate needs about 13,000-14,000 BTU/hr of cooling, which means a 15,000 BTU rooftop unit. In a moderate climate or with regular shade, a 13,500 BTU unit covers it. Run your exact conditions through the calculator above - climate and shade move the answer more than a foot or two of length does.

Is 13,500 BTU enough for my camper?

For most rigs up to about 26-27 feet (under ~300 sq ft), yes - 13,500 BTU is the sweet spot. It handles travel trailers and Class C motorhomes in hot climates and runs long enough cycles to actually dehumidify the air. Where it falls short: rigs pushing 30+ feet, desert heat above 105°F, or full-sun parking with an older, poorly insulated rig.

Should I buy a 13,500 or 15,000 BTU RV air conditioner?

Buy the size the load calls for - not the bigger one 'just in case.' On a small rig, a 15,000 BTU unit cools so fast the compressor short-cycles: it slams on and off constantly, never runs long enough to pull humidity out, and wears out years early. The 13,500 runs longer, leaves the air drier, and lasts longer. Choose 15,000 only when the rig is 27+ feet, the climate is brutal, or the calculator's load lands above about 12,700 BTU.

Can I run my RV air conditioner on a 30-amp hookup?

One rooftop AC, yes - a 13,500 BTU unit draws about 12-13 amps running and a 15,000 BTU about 14-16 amps, well within a 30-amp (3,600W) pedestal. The catch is everything else: the AC plus an electric water heater plus a microwave will trip the breaker. Two AC units cannot run together on 30 amps; that requires 50-amp service or an energy-management system that alternates them.

What size generator do I need to run an RV air conditioner?

The startup surge decides it, not the running draw. A 13,500 BTU unit surges 55-70 amps for a split second, so plan on a 3,000W generator; a 15,000 BTU unit needs about 3,600W. Install a soft start module and the picture changes completely: the surge drops to 25-35 amps, and a 2,200W inverter generator will start a 13,500 BTU unit.

What is a soft start, and do I need one?

A soft start module (MicroAir EasyStart is the best-known) ramps the compressor up gradually instead of letting it slam on at 65-85 locked-rotor amps. It cuts the startup surge by roughly 60-70%. You need one if you run the AC on a generator under 3,500W, on batteries/solar while boondocking, or on a shared 30-amp circuit that keeps tripping. On full shore power it's a nice-to-have, not a must.

When does an RV need two air conditioners?

Past about 32 feet, one rooftop unit can't distribute air evenly no matter how many BTUs it has - the bedroom at the far end stays hot. Big travel trailers, 5th wheels, Class A motorhomes, and toy haulers in that range run two units (typically 13,500 or 15,000 BTU each, front and rear), and 40+ foot rigs sometimes run three. Remember: two units require 50-amp service to run simultaneously.

Why is my RV AC loud and barely cold even though it's the right size?

Very often it's the factory installation, not the unit. Manufacturers routinely leave gaps in the plenum (the air box between the unit and your ceiling), so cold supply air short-circuits straight back into the hot return - RV owners who seal the plenum with foil tape and add a foam divider between the hot and cold sides report airflow gains of 40% or more, plus a big drop in noise. Before replacing a unit that measures fine, pull the ceiling shroud and seal the leaks.

Can I run an RV air conditioner on batteries or solar?

Yes, with the right setup: a soft start (mandatory), an inverter sized for ~1,500-2,000W continuous, and a serious battery bank - a standard 13,500 BTU unit pulls roughly 120 amps per hour from a 12V bank. That's why boondockers favor the new inverter-driven, variable-speed rooftop units: instead of cycling at 100% power, they ramp down to match the load and roughly halve the average draw, doubling AC runtime per battery charge.