Solar & Battery Electrical Calculator for Campervans | VanPowerCalc

Leo

Here's the uncomfortable truth about van climate control: heating is basically free electrically (0.5-1A for a diesel heater running), but cooling will destroy your battery bank. A 12V rooftop AC unit pulls 40-60A sustained — that's 480-720W continuously, draining a 200Ah LiFePO4 battery in 3-4 hours. I spent two summers in southern Spain figuring out what actually works without a 400Ah bank and 800W of solar.

Let's break down the real numbers. A diesel heater (like a Chinese 2kW or Webasto): 0.5-1A running draw, but the glow plug startup hits 5-6A for 2-3 minutes. Over a cold night (10 hours), that's roughly 8-12Ah — trivial. A MaxxFan or Maxxair on medium speed: 1-3A, so 10-30Ah overnight. Totally manageable. Now the pain: a 12V compressor AC unit (like the Dometic RTX 2000) pulls 40-60A. Running it for 6 hours on a hot day = 240-360Ah consumed. You'd need a 400Ah LiFePO4 bank minimum and at least 600W of solar just to partially offset that. Most van builds can't support real AC — that's the honest answer nobody wants to hear.

Park facing north (in the northern hemisphere) and put Reflectix on your windshield and side windows. Combined with a MaxxFan exhausting hot air from the ceiling, this setup drops interior temps by 10-15 degrees versus a sun-facing unshielded van — and draws just 2A.

I've tried pretty much everything over five years of full-time van life across different climates. Here's what I've learned the hard way.

For heating, a diesel heater is the only sane choice in a van. Propane works but adds moisture inside (about 1 liter of water per liter of propane burned), and electric ceramic heaters need a massive inverter and battery bank. My Chinese 5kW diesel heater cost 120 euros and runs all winter on 0.8A. The fuel consumption is about 0.1-0.3L/hour depending on the setting. My 200Ah LiFePO4 doesn't even notice it.

For cooling, accept that you have three tiers. Tier 1 is a good roof fan (MaxxFan Deluxe) pulling hot air out while cracking a window for intake — 1-3A, works down to about 5 degrees above outside temperature. Tier 2 is a portable evaporative cooler — 2-5A, only works in dry climates (below 40% humidity), drops temperature 5-10 degrees. Tier 3 is real AC — 40-60A at 12V, works everywhere, but demands a serious electrical system.

The part most guides skip is insulation. I've seen people spend 3,000 euros on batteries and solar to run AC in a van with zero insulation. A well-insulated van (3M Thinsulate or closed-cell foam on walls, floor, ceiling, plus reflective window covers) drops your interior temperature by 8-12 degrees compared to bare metal. That's free — no power draw.

My setup after years of iteration: 5kW diesel heater for winter (8Ah/night), MaxxFan Deluxe for spring/fall (15Ah/night), reflective window covers + MaxxFan for summer, and I simply don't park in direct sun during heat waves. If I truly need AC, I go to a campsite with shore power. The electrical cost of real van AC is so extreme that it changes your entire system sizing — 400Ah batteries, 800W+ solar, 50mm² cable runs. Build for it from day one or don't bother.

A diesel heater draws 0.5-1A while running at 12V, so just 6-12W. The startup phase is higher at 5-6A for 2-3 minutes while the glow plug heats up. Over a full cold night (10 hours), expect 8-12Ah total consumption — a 100Ah battery barely notices it.

Technically yes, practically it's brutal. A 12V rooftop AC unit draws 40-60A continuously. Running it for 6 hours consumes 240-360Ah. You'd need at minimum a 400Ah LiFePO4 bank, 600W+ of solar, and 50mm² cable runs. Most van builds aren't sized for this. I'd recommend shore power for AC or redesigning your entire electrical system around it.

A MaxxFan Deluxe (or similar powered roof vent) at 1-3A draw, combined with reflective window covers and parking in shade. It won't match real AC, but it drops interior temps by 10-15 degrees for a fraction of the electrical cost. In dry climates, add a 12V evaporative cooler for another 5-10 degree drop at 2-5A.

Huge difference. A properly insulated van (closed-cell foam or Thinsulate on all surfaces, plus reflective window covers) runs 8-12 degrees cooler in summer and retains heat dramatically longer in winter. It's zero ongoing power draw. I'd spend money on insulation before upgrading batteries for AC.

For most van builds, no. A 120 euro Chinese 5kW unit and a 1,200 euro Webasto do the same job. The Chinese units are noisier, slightly less fuel-efficient, and the build quality is rougher. But they work. I've run one for three winters without issues. If you want whisper-quiet and bulletproof reliability, Webasto. If you want heat and have better things to spend 1,000 euros on, go Chinese.

Current (A)	Round trip < 2m	Round trip 4m	Round trip 6m
5A (LEDs, USB)	1.5 mm²	2.5 mm²	4 mm²
10A (Fridge, Pump)	2.5 mm²	4 mm²	6 mm²
20A (Heater)	4 mm²	10 mm²	10 mm²
50A (DC/DC Booster)	10 mm²	16 mm²	25 mm²
100A (Inverter)	25 mm²	35 mm²	50 mm²

Appliance	Power	Usage/day	Wh/day
Compression fridge	45W	24h	1080
LED lighting	20W	4h	80
Water pump	30W	0.5h	15
Phone charging	15W	2h	30
Daily consumption			1205 Wh

Climate Control in a DIY Van — What It Actually Costs in Watts

Your electrical appliances

Build custom

Battery

Solar

220V AC

12V Cable Sizing Guide

Fuse Sizing

SCHÉMA ÉLECTRIQUE

PANNEAUX SOLAIRES

RÉGULATEUR MPPT

BATTERIE AUXILIAIRE

BOÎTE À FUSIBLES 12V

CONVERTISSEUR 220V

Example calculation for your setup

About this tool

Frequently asked questions

Independent and free thanks to your clicks

Recommended gear

Related tools