Van Life 12 min read

Van in summer: ventilation or 12 V air conditioning?

By Azimut AI · September 21, 2026 · Our editorial policy

A van insulated for winter and parked in full sun in August is a very well-insulated oven. That is what the hot season makes brutally clear: insulation does not cool anything — it slows the heat coming in, it does not take it out. Only moving air, or a machine, removes calories. Here is the ladder of levers, with the watt-hours each one costs.

70–80 °C

dark roof exposed to full sun

0.1–0.3 kWh

roof fan over a full night

0.8–1.5 kWh

12 V air conditioning over a night of cycling

8–15 °C

indoor gap between full sun and shade

Where the heat gets in — and why insulation is not the answer

Insulation produces no cold: it slows a flow, in both directions. In the morning it delays the temperature rise — that is welcome. After midday it also delays the fall: the heat already inside stays trapped in the evening, when the outside air has become breathable again. It is the same wall that saves a February night and ruins an August one.

The hierarchy of entry points is counter-intuitive. The roof comes far ahead: it is the largest surface facing the sun and the only one receiving it almost vertically during the hot hours; dark sheet metal there routinely reaches 70 to 80 °C. Then come the windows, which slow nothing at all — radiation passes straight through and turns into heat inside, on whatever surfaces it lights up. The walls, which everyone insulates first, only come third. In other words: the insulation project that saves your winter changes almost nothing in August. What does change something is stopping radiation before it arrives, or removing the heat already inside.

The ladder of levers: shade, ventilation, air conditioning

0 Wh — shade and orientation

A van in shade can run 8 to 15 °C cooler inside than the same van in full sun, depending on the season and how long it has been exposed: no piece of equipment offers that return. Turning the smallest glazed side towards the afternoon sun costs nothing. External reflective covers stop radiation before the glass, which no internal curtain can do. And geography stays the most underrated lever: roughly -6 °C per 1,000 m of elevation, or a sea breeze that picks up after 4 pm.

0.1–0.3 kWh per night — ventilation

A roof fan moves roughly 600 to 1,000 m³/h at full speed, against a habitable volume of 6 to 8 m³: one to three air changes per minute. It draws 0.5 to 3 A depending on speed, so 6 to 36 W — a full night at the usual speeds fits inside 0.1 to 0.3 kWh, within reach of any bank, and full speed without a break costs more. One condition is non-negotiable: air must be able to get in. With a single opening the fan fights itself; two opposed openings create a through-flow.

0.8–1.5 kWh per night — 12 V air conditioning

A 12 V compressor unit draws 400 to 800 W while the compressor runs; over a night of cycling, expect 0.8 to 1.5 kWh depending on insulation, outside temperature and setpoint. That is five to ten times the fan — for genuinely better comfort, but only when the outside air stays above roughly 28 °C at night. Below that, ventilation does the same job for a tenth of the energy.

What 12 V air conditioning really requires — and when it is right

Running a 12 V air conditioner off-grid is not a comfort question, it is an energy problem posed upstream. The orders of magnitude to hold simultaneously:

• The bank — of the order of 200 Ah LiFePO4 to absorb a night of cycling without dropping into the zone where the BMS starts protecting. In lead-acid, the same night calls for double the nominal capacity.
• The recharge — of the order of 400 Wp of solar to put that night back into the bank during the following day. And this is a peak-season calculation: in July, solar is at its best. One night at a time, not two in a row under a hazy sky.
• The fridge, a second-order effect — it works far harder in heat: its consumption can nearly double at 35 °C ambient. The hot day therefore costs energy before anything has been switched on.
• The contradiction worth knowing — the shade that keeps you cool kills your solar. Parking under trees and counting on the panels to repay the night does not work: you choose, or you move the panels.

Air conditioning is the wrong call for a one-night stop, at an altitude bivouac, on a ventilated coastline: shade and a roof fan are enough there, and the mass, the price and the hole in the roof never pay themselves back. It is the right call for a stationary summer on a hot plain, when you work inside the van in full daylight, or when nights stay tropical for weeks. One last thing, said once: a closed van in the sun kills an animal or a small child within minutes. Ventilation does not make an unattended vehicle safe — no equipment replaces presence.

Key takeaways

Insulation does not cool: it slows heat in both directions. A van insulated for winter and parked in the sun is a well-insulated oven.
Hierarchy of entry points: the roof first (70 to 80 °C on dark sheet metal), then the windows, and the walls only third.
Shade is the highest-return lever: 8 to 15 °C of indoor difference without a single watt, plus roughly -6 °C per 1,000 m of elevation.
Ventilation: 6 to 36 W depending on speed, so 0.1 to 0.3 kWh over a night at the usual speeds — provided you open a second air inlet, otherwise the fan fights itself.
12 V air conditioning: 400 to 800 W while running, 0.8 to 1.5 kWh per night, so a bank of the order of 200 Ah LiFePO4 and 400 Wp — one night at a time.

FAQ

Roof fan or portable fan?

They do different jobs. The roof fan acts on the van: it extracts hot air from the volume and replaces it with outside air, so it lowers the actual temperature as soon as outside is cooler than inside. The portable fan acts on the body: it does not cool the cabin, it speeds up sweat evaporation and buys a few degrees of perceived comfort for 2 to 5 W. The logical order is to fit the first and add the second as a complement, not the other way round.

Can 12 V air conditioning run all night on battery?

Yes, with a bank of the order of 200 Ah LiFePO4 and around 400 Wp of solar — but one night at a time: the following day has to put everything back before the next night. Two consecutive tropical nights under a hazy sky, or a parking spot chosen in the shade precisely for the coolness, and the balance no longer closes. Air conditioning is self-sufficient only as long as tomorrow's sun pays for last night.

Should you insulate differently for mostly summer travel?

The lever that matters in summer is not thickness but the outer surface and its ventilation: a light-coloured roof rather than a dark one, a reflective cover fitted outside, and a ventilated air gap under the roof lining so the roof's heat does not radiate straight into the cabin. Stacking centimetres of insulation beyond the usual few adds mass and cost for a summer gain close to zero — it is winter that repays that thickness, not summer.