Solar & Battery Electrical Calculator for Campervans | VanPowerCalc

Q: Is a 2kW diesel heater enough for a van in winter?

For a well-insulated van under 14m³ (Sprinter 144", Transit L3), a 2kW heater holds 20°C down to about -5°C to -15°C outside, depending on insulation quality. It produces about 6,800 BTU/h at full output, which covers most winter camping scenarios.

Q: How much fuel does a diesel air heater use?

A 2kW heater uses 0.04-0.12 L/hour (low to high). A 5kW uses 0.12-0.24 L/hour. An 8kW uses 0.18-0.38 L/hour. A 10L tank on a 2kW unit running at medium lasts roughly 5-8 days of overnight heating.

Q: Why does my Chinese diesel heater keep cycling on and off?

It is oversized for your space. When the heater reaches target temperature too fast, it shuts down, the van cools, and it restarts. This cycling fouls the glow plug and wastes fuel. Solution: use a smaller heater, or run the thermostat at a lower setting with the fan on medium.

Q: Does altitude affect diesel heater performance?

Yes. Combustion efficiency drops about 1% per 100m above sea level. At 2,000m elevation, expect roughly 20% less heat output. Size up if you regularly camp at altitude — a 2kW heater effectively becomes a 1.6kW unit at 2,000m.

Q: Chinese diesel heater vs Webasto — is the premium worth it?

The Chinese 2kW units ($80-150) produce the same heat as a Webasto Air Top 2000 ($800-1,200). The Webasto is quieter, better built, has proper service networks, and lasts longer with less maintenance. For occasional use, Chinese is fine. For full-time living, the Webasto pays for itself in reliability.

Leo

Updated Apr 21, 2026Fact-checked on Apr 21, 2026

Diesel Air Heater Sizing — How to Pick the Right kW for Your Van

Picking the right kW diesel heater for a van. BTU calc, van volume, insulation, altitude derating, and real fuel consumption numbers.

7 min read

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Your electrical appliances

Quick Add

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Daily Total

0

WH / Day

Tap a preset above to start

System Config

System Voltage

Average Sun Hours

VANPOWERCALC.COMYOUR 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

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.COM

I installed a 5kW Chinese diesel heater in my 12m³ well-insulated Sprinter and it was overkill. On low, it cycled on and off every few minutes. On high, it turned the van into a sauna in under 5 minutes. Most van builders buy too much heater because "what if it's really cold?" — but an oversized heater that constantly cycles is louder, burns more fuel, and carbon-fouls faster than a properly sized one running at a steady medium output. Let me walk you through the actual math so you get this right.

The core formula is simple: you need to calculate your heat loss in BTUs per hour, then match it to a heater's output. A 2kW heater produces about 6,800 BTU/h, a 5kW produces 17,000 BTU/h, and an 8kW produces 27,300 BTU/h. Your van's heat loss depends on three things: volume, insulation R-value, and the temperature difference between inside and outside (delta-T). A standard cargo van (Sprinter 144" or Transit L2) has roughly 10-14m³ of interior volume. With decent insulation (25mm polyiso on walls, 50mm on ceiling, insulated floor), your effective R-value averages around R-7 to R-10. Without insulation — bare metal walls — you're looking at R-1 to R-2, and you'll need dramatically more heat. For a well-insulated 12m³ van with R-8 walls aiming for a 30°C delta-T (keeping 20°C inside when it's -10°C outside), heat loss runs about 4,000-5,500 BTU/h. A 2kW heater at full blast covers that. A 5kW heater would run at 30-40% output, which is fine as long as it doesn't cycle.

12V cable sizing guide for RVs — vanpowercalc.com

Expert tip

Buy the smallest heater that covers your worst-case scenario. An oversized heater running on low will carbon up the glow plug and heat exchanger within one season. I'd rather run a 2kW heater at 80% than a 5kW at 20%. If you're between sizes, the smaller one running harder will last longer and burn cleaner.

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

151 Ah

(80% depth of discharge)

Recommended AGM battery

241 Ah

(50% depth of discharge)

Recommended solar panels

402 Wc

4h average sun hours

Recommended inverter

No 220V appliances — no inverter needed

Adjust these values with the calculator below

About this tool

Let me give you real sizing recommendations based on hundreds of van builds I've seen.

For a small van (VW Transporter, Ford Transit Custom, ~6-8m³ insulated): a 2kW heater is perfect. It'll hold 20°C down to about -15°C outside. At full output, fuel consumption is roughly 0.10-0.12 L/hour. On low, it sips about 0.04 L/hour. That means a 10L fuel tank lasts 4-10 days depending on conditions.

For a medium van (Sprinter 144", Transit L3, ~10-14m³ insulated): a 2kW heater still works down to about -5°C outside. If you camp in serious winter conditions regularly, a 5kW gives you headroom — just make sure you run it at medium, not low, to avoid the cycling problem. Fuel consumption on a 5kW at medium is about 0.16-0.20 L/hour.

For a large van or bus conversion (Sprinter 170", school bus, ~15-25m³): a 5kW is the minimum. For poorly insulated or very large builds over 20m³, the 8kW makes sense. An 8kW heater at full output burns about 0.30-0.38 L/hour.

Altitude derating matters and almost nobody accounts for it. Diesel combustion efficiency drops about 1% per 100m of elevation above sea level. At 2,000m (6,500 ft), your heater loses roughly 20% of its rated output. A 5kW heater effectively becomes a 4kW heater. If you ski camp or boondock at altitude regularly, size up.

One more factor: windows. Glass is a thermal disaster — R-value of about R-1. A van with a large rear window and two side windows loses significantly more heat than one with solid insulated panels. Each square meter of single-pane glass adds roughly 800-1,000 BTU/h of heat loss at a 30°C delta-T.

The Chinese diesel heaters (Vevor, Hcalory, generic "all-in-one" units) work surprisingly well for the price. The 2kW units run $80-150, the 5kW units $100-200. They're noisy on high (the combustion fan is the main culprit) but at medium to low output, cabin noise is typically 40-50 dB. The Webasto Air Top 2000 STC and Eberspacher Airtronic D2 are the premium alternatives at $800-1,200 — quieter, better built, and easier to get serviced, but the heating output is comparable to a Chinese 2kW unit.

ByLeo—Electrical Engineer & VASP Builder

Published April 1, 2026

Frequently asked questions

Is a 2kW diesel heater enough for a van in winter?▼

For a well-insulated van under 14m³ (Sprinter 144", Transit L3), a 2kW heater holds 20°C down to about -5°C to -15°C outside, depending on insulation quality. It produces about 6,800 BTU/h at full output, which covers most winter camping scenarios.

How much fuel does a diesel air heater use?▼

A 2kW heater uses 0.04-0.12 L/hour (low to high). A 5kW uses 0.12-0.24 L/hour. An 8kW uses 0.18-0.38 L/hour. A 10L tank on a 2kW unit running at medium lasts roughly 5-8 days of overnight heating.

Why does my Chinese diesel heater keep cycling on and off?▼

It is oversized for your space. When the heater reaches target temperature too fast, it shuts down, the van cools, and it restarts. This cycling fouls the glow plug and wastes fuel. Solution: use a smaller heater, or run the thermostat at a lower setting with the fan on medium.

Does altitude affect diesel heater performance?▼

Yes. Combustion efficiency drops about 1% per 100m above sea level. At 2,000m elevation, expect roughly 20% less heat output. Size up if you regularly camp at altitude — a 2kW heater effectively becomes a 1.6kW unit at 2,000m.

Chinese diesel heater vs Webasto — is the premium worth it?▼

The Chinese 2kW units ($80-150) produce the same heat as a Webasto Air Top 2000 ($800-1,200). The Webasto is quieter, better built, has proper service networks, and lasts longer with less maintenance. For occasional use, Chinese is fine. For full-time living, the Webasto pays for itself in reliability.

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