Most of the Coleman-Mach range comes in 13,500 or 15,000 BTU, and the two cost within $150 of each other. Sizing is about three things: length, sun and ducting.
Rule of thumb by RV length
| RV | Mild climate (highs under 90F) | Hot climate (FL, TX, AZ, Gulf Coast) |
|---|---|---|
| Travel trailer 20 to 26 ft | 13,500 | 13,500, or 15,000 if dark exterior |
| Travel trailer 26 to 32 ft, single AC | 13,500 | 15,000 |
| Travel trailer or fifth wheel 30 to 36 ft, ducted | 15,000 | 15,000, consider a second unit |
| Fifth wheel or motorhome over 36 ft | Two units, 15,000 front | Two 15,000, or three |
Under 20 ft (teardrops, pop-ups, vans): the smallest unit we stock is 13,500 BTU, which is more than most rigs that size need. Coleman-Mach makes smaller units, but we do not sell them, so we do not size them here.
Why ducted rigs want 15,000
Ducting loses cooling to the ceiling cavity and the duct runs, so a 13,500 unit that cools a 28 ft non-ducted trailer fine will feel undersized pushing air through 30 ft of duct. If the ceiling has vents along it, buy the 15,000.
Why bigger is not always better
An oversized unit short-cycles: it hits set point fast, shuts off, and never runs long enough to pull humidity out. In Florida that means a cold, clammy trailer. For a small trailer in a humid climate, the 13,500 running longer is the better result. Oversizing also matters on a generator; see the generator guide.
Replacing an existing unit
If the old unit kept up on the hottest days, replace it with the same BTU. If it ran all day and never got the trailer under 80F, step up one size, or add a second unit if the rig is over 32 ft. Going from 13,500 to 15,000 in the same Coleman-Mach family changes nothing about the install: same opening, same ceiling assembly, same controls.
Shop by output: 13,500 BTU, 15,000 BTU, 18,000 BTU.