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Fact-checked on Apr 8, 2026
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.
⚡ Expert tip
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.
Example calculation for your setup
Results based on a typical use case
| 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 | ||
Recommended LiFePO4 battery
126 Ah
(80% depth of discharge)
Recommended AGM battery
201 Ah
(50% depth of discharge)
Recommended solar panels
302 Wc
4h average sun hours
Recommended inverter
No 220V appliances — no inverter needed
Adjust these values with the calculator below
VANPOWERCALC PROYOUR ENERGY PROFILE
YOUR ENERGY PROFILE.
This document contains the sizing of your future electrical installation, calculated based on your appliances.
Minimum Daily Consumption
0 WH / DAY
Inventory:
SYSTEM SIZINGPage 2
Battery
To guarantee 0WH without damaging your bank (80% max discharge):
0 AH
LiFePO4 12V
Solar
Minimum power required to recharge your consumption:
0 W
via MPPT
220V AC
Maximum power (with 25% safety margin).
0 W
No Need
Safety & CablingPage 3
12V Cable Sizing Guide
Use this professional reference table to select the correct gauge (mm²) for your cables. For 12V in a van, the maximum tolerated voltage drop is 3%. Always use multi-stranded flexible automotive wire.
| 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 |
Fuse Sizing
The fuse protects the wire, not the appliance. Always place it as close to the power source as possible (battery or busbar).
- Wire 1.5 mm² → Max fuse 10A
- Wire 2.5 mm² → Max fuse 20A
- Wire 4 mm² → Max fuse 30A
- Wire 6 mm² → Max fuse 40A
- Wire 10 mm² → Max fuse 60A
SCHÉMA ÉLECTRIQUE
PANNEAUX SOLAIRES
0W
RÉGULATEUR MPPT
BATTERIE AUXILIAIRE
0 Ah
Lithium LiFePO4
FUSIBLE
FUSIBLE
BOÎTE À FUSIBLES 12V
Pompe, Leds, Frigo...
CONVERTISSEUR 220V
NON REQUI
PRO GEARPage 4
SHOPPING LIST
Where to find this equipment? Here is the community-approved selection.
12V 6-way Fuse Box
Mandatory protection
Digital Multimeter
Test your connections
Heavy Duty Crimping Tool
For perfect lugs
Heat Shrink Tubing
Insulation and safety
GENERATED BY VANPOWERCALC PRO - UNLIMITED.
About this tool
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.
Frequently asked questions
How much power does a diesel heater use in a camper van?▼
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.
Can I run air conditioning in a van off batteries?▼
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.
What's the best cooling solution for a van on a budget?▼
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.
Does van insulation really make a difference for climate control?▼
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.
Chinese diesel heater vs Webasto — worth the price difference?▼
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.
The links below are Amazon affiliate links. If you purchase through these links, I earn a small commission — at no extra cost to you. This is what allows me to keep this site free.
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