Does a 12 Volt Swamp Cooler Work in an RV or Van?

A 12 volt swamp cooler does work in an RV or van, as long as the air outside is dry. A 750 CFM roof unit like the TurboKool 2B-0001 draws only 2.2 to 4.6 amps, so the battery is rarely the problem. Water is. At a 20 F temperature drop that cooler evaporates about 1.8 gallons per hour, roughly 22 gallons over a 12 hour day, which is about seven times the "approximately 3 gallons per day" printed on a retail listing.

What a 12 V RV cooler actually is

The best-known purpose-built unit is the TurboKool 2B-0001. It is a direct evaporative cooler: a fan pulls outdoor air through a wetted pad and blows it into the rig, the same principle explained in how evaporative coolers work, just shrunk to fit a roof vent.

The two sources disagree slightly on peak current (4.6 A vs 4.8 A) and on the humidity ceiling (75% vs 70%). The battery math below shows both currents; the humidity ceiling is too generous either way.

Homemade builds are the other option. BuildItSolar's DIY RV cooler draws about 18 watts at 12 volts and reports a drop of as much as 25 F; see our DIY swamp cooler guide for plans and limits.

Is 750 CFM enough for your rig?

The site sizes every cooler by air changes per hour: about 40 in hot desert, 30 in moderate dry climates. Apply that to two example interiors (use your own measured inside dimensions):

Rated airflow is a ceiling; delivered airflow through a wet pad is lower, as the portable cooler buying guide explains.

Battery: amp-hours at each speed

Amp-hours are amps times hours. At 12 V nominal, the listed currents are about 26 W on low, 38 W on medium and 55 W on high. BuildAGreenRV puts the TurboKool at about 50 W against roughly 1,000 W for a conventional rooftop air conditioner.

The usable capacity columns follow Victron's guidance: a 100 Ah AGM battery gives about 50 Ah of safe daily use, while a 100 Ah lithium battery gives about 80 to 100 Ah. If the cooler fills from your pressurized fresh water system, the coach water pump also runs briefly each time the float valve calls for water. That load is not in the table.

Water: 3 gallons a day or 1.6 gallons an hour?

Both numbers circulate, and they cannot both be right for the same cooling. Evaporation follows directly from how much heat the cooler removes. The site uses the same formula in bleed-off and water quality and swamp cooler water usage:

So the physics figure is right, and the 3 gallons per day figure only fits a cooler that runs briefly, runs on low airflow, or barely cools. The listing does not state the conditions behind it, and it is the only water number on the product page, which is why it gets repeated. The same page claims a 20 to 30 F drop, which takes 1.8 to 2.7 gallons per hour.

Water use scales with airflow too. If the unit only delivers two thirds of its rating, take two thirds of these figures. The water usage calculator runs the same arithmetic for any airflow and drop.

A fresh-tank budget

On a city water hookup none of this matters. Boondocking, the cooler competes with drinking, cooking and washing for the same tank:

The listing says the unit can draw from an external tank, so a dedicated container can protect your drinking supply. The reservoir also concentrates minerals as water evaporates; with hard water, see scale removal and prevention.

Where it works: the wet bulb cutoffs

A cooler can never drop the air below the outdoor wet bulb temperature, and in practice it only gets part of the way there. That puts a hard ceiling on the 20 to 30 F claim: the drop can never exceed the gap between dry bulb and wet bulb.

Compare that with the listings' "average relative humidity not over 70%" or "75%". At 95 F, 30% RH already gives a 72 F wet bulb and only a 23 F gap; 40% RH gives 76 F and a 19 F gap. At 60% RH the wet bulb is about 83 F. A 70% ceiling therefore allows conditions where the cooler can barely cool at all. Use wet bulb or dew point instead; the full reasoning is in do swamp coolers work in humidity, and the climate index lists typical conditions by city.

For RVers this makes it a Western dry-season tool: excellent in the high desert and Great Basin in early summer, weaker during monsoon surges, and close to useless on the Gulf Coast in August.

Give the air somewhere to go

A roof cooler pushes 750 cubic feet of damp air into the rig every minute. If it cannot get out, humidity climbs, the wet bulb inside rises and the cooling fades. The site's field rule is about 1 to 2 sq ft of opening per 1,000 CFM, so a 750 CFM unit wants roughly 108 to 216 sq in open: a 12 x 12 in window is 144 sq in. Open it at the far end from the cooler. The listing mentions a reversible motor for exhaust use, but while the unit is cooling it is your intake, so the exhaust opening has to be somewhere else. Details are in venting and relief air.

Where this answer stops applying

• Humid regions. Above about a 75 F wet bulb, no amount of amp-hours or water makes it a cooler.
• Large rigs. Past roughly 25 ft or with slides open, one 750 CFM unit falls short of the desert air-change target.
• Other models. The figures here are for a 750 CFM, 2.2 to 4.6 A unit. For any other cooler, use its own current draw and airflow in the same formulas.