There are three practical ways to air-condition a van or RV today: a traditional 120V-class rooftop unit, a DC rooftop unit that runs straight from the battery bank, or a portable unit that sits inside and vents out. Each one wins in a different situation. This guide compares them using real products we carry: the Dometic Penguin II rooftop, the Nomadic Cooling X2 and X3 Helix DC rooftops and S1 Helix split, and the Zero Breeze Mark 3 and Cybertake S2 Pro portables. Specs come from each maker's figures as published on their own pages or our listings.
The three options in one table
| 120V rooftop (Dometic Penguin II) | DC rooftop (Nomadic X2 / X3 Helix) | Portable (Zero Breeze Mark 3, Cybertake S2 Pro) | |
|---|---|---|---|
| Power | 115V AC per Dometic: shore power, a generator or a large inverter | 12V or 48V DC straight from the battery bank, no inverter | Mark 3: 48V DC from its own Smart Battery. S2 Pro: 100–240V AC, 12V/24V vehicle, or 48V with a converter |
| Cooling | High-capacity rooftop | X2: ~8,950 BTU/hr Full AC planning average (12V). X3: ~12,893 BTU/hr (12V, provisional) | Mark 3: 5,280 BTU. S2 Pro: 5,100 BTU |
| Draw | Running load plus starting surge, through an inverter when off-grid | X2 12V: ~526 W ECO, ~871 W Full AC. X3 12V: ~899 W ECO, ~1,297 W Full (provisional) | Mark 3: 500 W rated, 150 W minimum once holding temperature |
| Install | 14 x 14 in roof opening, ducted or non-ducted | 14 x 14 in roof opening plus DC cable and fuse | No roof work; needs a vent kit or window/door venting |
| Best for | Rigs that camp on hookups or run a generator | Off-grid vans, truck campers and trailers with a large lithium bank | Tents, small vans, renters, or a second cool zone |
120V rooftop: the classic choice
The Dometic Penguin II is the kind of rooftop unit most RVs leave the factory with. It drops into a standard 14 x 14 in roof opening, works with ducted or non-ducted ceilings, and Dometic lists it as a 115-volt AC unit. On shore power or a generator that is ideal: big cooling capacity with no battery math.
The catch is off-grid. Running a 120V roof air conditioner from batteries means an inverter, a large bank and the starting surge on top of the running load. Our answer on whether lithium can run a roof A/C for 8 hours works through why that rarely adds up, and a soft start helps with the surge but not with the running load. If you camp mostly on hookups, a 120V unit is still the simplest answer. Installing one? See the Penguin II install guide.
DC rooftop: built for the battery bank
A DC rooftop unit takes the inverter out of the picture. The Nomadic X2 Helix Gen II runs straight from a 12V or 48V bank with a PWM compressor that ramps and holds temperature rather than hard on/off cycling. Nomadic says plainly that it does not need an inverter like a traditional 120V AC rooftop unit. It still uses the familiar 14 x 14 in opening, so the roof side of the job is the same as a classic rooftop.
Nomadic's planning averages for the X2 on 12V are about 526 W on ECO and about 871 W on Full AC. At 526 W, a 400 Ah 12V LiFePO4 bank (about 4,608 Wh usable at 90%) runs it for about 8.8 hours if it holds that average all night with no other loads. That is the kind of off-grid night a 120V unit through an inverter struggles to deliver from a bank that size. The larger X3 Helix gives more cooling for a bigger cabin, with provisional figures of about 899 W on ECO and 1,297 W on Full AC at 12V, so it needs a bigger bank. Full tables: how much battery to run a Nomadic air conditioner.
The trade-offs: the battery bank, charging and wiring have to be designed for a large DC load. A 12V X2 draws up to 64 A at its rated maximum, so cable, fusing and the battery's BMS limits all matter. See our 12V vs 48V guide.
No room on the roof?
The Nomadic S1 Helix is a DC split system: the condenser mounts on a rear wall and the evaporator inside. It keeps the roof free for solar and does not add height. Nomadic's planning figures put it at about 486 W on ECO and 879 W on Full AC on 12V. Its refrigerant connections need a licensed technician to evacuate and charge.
Portable: no roof work at all
Portable units sit inside the rig and vent hot air outside through hoses. They are the easiest to fit and take with you, but they cool a smaller space.
- Zero Breeze Mark 3: 5,280 BTU cooling for roughly 100–150 sq ft, 48V DC at 500 W rated and 150 W minimum once holding temperature, just under 22 lb. It runs from its own 1,022 Wh 48V Smart Battery, and a vent kit is required.
- Cybertake S2 Pro: 5,100 BTU cooling and 6,100 BTU heating for spaces up to 130 sq ft. It runs from wall power, 12V/24V vehicle power, or 48V from a power station with a converter, and Cybertake says up to 8 hours on 1 kWh in Eco+ mode.
Portables suit tents, small vans, people who cannot cut the roof, or a second cool zone in a bigger rig. Venting matters a lot to how well they work; see how to vent a portable air conditioner and our earlier comparison of portable vs rooftop units.
How to choose
- Mostly on hookups or with a generator: a 120V rooftop such as the Penguin II.
- Off-grid with a large lithium bank and solar: a DC rooftop, the X2 Helix Gen II for small to mid cabins or the X3 Helix for larger ones.
- Off-grid but no roof space, or a height limit: the S1 Helix split.
- No roof cut, a small space, or you want to move it between vehicles: a portable such as the Zero Breeze Mark 3 or Cybertake S2 Pro.
Whichever way you go, size the cooling to the space first with our BTU sizing guide, then check the power side with the solar and battery calculator.
Questions
Is a DC air conditioner as strong as a 120V rooftop unit?
Not the compact X2. Nomadic's X2 planning average is about 8,950 BTU/hr on Full AC at 12V, while conventional 120V rooftop units are commonly sold in 13,500 and 15,000 BTU sizes (Dometic's Penguin II line includes both). The trade is that the X2 runs from batteries without an inverter. The X3 Helix's provisional figures go higher, for larger cabins.
Can I replace my 120V rooftop unit with a Nomadic DC unit?
The X2 and X3 fit the standard 14 x 14 in opening, so the roof side often lines up. The electrical side is new work: heavy DC cable and a fuse from the battery bank, and a bank big enough to carry it. Check your existing opening, roof structure and ceiling ducting before you order. See our Nomadic install guide and the general RV air conditioner replacement guide.
Do portable units need an inverter?
Not always. The Mark 3 runs from its own 48V battery, and the S2 Pro can run from 12V/24V vehicle power or wall power.
Where do these ship from?
Everything here ships from our warehouse in Upland, California. Browse Nomadic Cooling, Dometic, Zero Breeze and Cybertake, or ask us which fits your rig.