A diesel heater is one of the best upgrades you can make to a campervan in the UK. It makes winter trips comfortable, helps with condensation, and means you can camp without relying on hookup.
But heaters also cause a lot of problems when they’re badly installed: fumes, noisy operation, soot build-up, battery drain, and unsafe exhaust routing.
This guide explains the basics in plain English — what size to choose, what a safe install looks like, and the red flags to watch for when you’re buying a converted van or booking a converter.
Safety note: This guide is general advice. Heaters must be installed correctly. If you’re unsure, use a professional installer.
Quick answer: should you choose 2kW or 5kW?
For most UK campervans (Transporter / Transit Custom / Vito / small conversions):
✅ 2kW is usually the right choice
For bigger vans (Crafter / Sprinter / Ducato / full-size panel vans, or lots of air volume):
✅ 5kW can make sense
A 5kW in a small van often runs too low, soots up, cycles on/off, and can be noisier. The “bigger is better” idea doesn’t usually apply here.
1) What a diesel heater actually does (and why it’s so popular)
A diesel heater:
- burns a small amount of diesel
- blows warm air into the living area
- uses 12V power for the fan and glow plug on start-up
- is much cheaper to run than most electric heaters off battery
In the UK, it’s mainly used for:
- cold weather camping
- drying wet coats/boots
- reducing condensation
- making shoulder seasons (spring/autumn) comfortable
2) Typical van sizes: what heater size suits what?
2kW is usually best for:
- VW Transporter T5/T6/T6.1
- Transit Custom
- Vito/Viano
- Small day vans with pop-tops
- Most “weekend camper” builds
5kW is more suitable for:
- VW Crafter / Sprinter
- Ducato / Boxer / Relay
- Big vans with a lot of insulation + high roof + large internal volume
- Vans used in truly cold conditions, or where you want rapid warm-up
Rule of thumb: If your van is “Transporter size”, start at 2kW unless there’s a special reason.
3) Running costs (rough UK reality)
Diesel heater fuel use depends on power level and conditions.
Typical ballpark:
- Low power steady running: modest diesel use
- High power startup/warm-up: higher
- Real cost depends on outside temp, insulation, venting, and how you use it
The bigger issue than fuel cost is usually:
✅ battery voltage drop during startup and poor installs that cause soot.
4) The two biggest causes of diesel heater problems
Problem #1: Sooting (especially with oversized heaters)
Soot happens when a heater:
- runs too low for too long
- short-cycles on and off
- doesn’t get hot enough to burn cleanly
Oversized heaters in small vans are a common cause.
Problem #2: Installation faults
Bad installs cause:
- fumes smells
- noisy pump tick
- vibration/rattles
- repeated failed starts
- unsafe exhaust routing near plastics/underseal
5) The safest “good install” checklist (what you should look for)
If you’re paying a converter or buying a converted van, look for these:
A) Exhaust routing
✅ Good:
- exhaust routed safely away from plastics, fuel lines, brake lines
- heat shield or clearance where needed
- secure mounting (won’t rattle loose)
- exhaust outlet not blowing into the van’s underside cavities
🚩 Red flags:
- exhaust pointed at underseal / body panels too close
- exhaust near sliding door step area with little clearance
- loose clamps, floppy exhaust sections
B) Combustion air intake
✅ Good:
- intake positioned to avoid sucking road spray directly
- fitted securely
- not blocked by underbody parts
🚩 Red flags:
- intake hanging low and exposed
- intake close to exhaust outlet (can cause issues)
C) Fuel line and pump
✅ Good:
- fuel line protected and routed neatly
- pump mounted at the correct angle (most pumps need a slight incline)
- pump mounted on a rubber isolator to reduce noise
- proper fuel filter (where appropriate)
🚩 Red flags:
- pump fixed directly to metal (tick-tick-tick through the whole van)
- fuel line kinked or rubbing sharp edges
D) Warm air ducting and vent
✅ Good:
- ducting is short and smooth (not crushed)
- outlet placed where it actually heats the living area
- a return air path exists (heater can breathe)
🚩 Red flags:
- crushed ducting or lots of tight bends
- outlet too close to curtains/soft trim
- heater boxed in with no air circulation
E) Electrical supply & fusing
✅ Good:
- dedicated fused supply from leisure battery
- correct cable size (heater startup draw matters)
- solid ground/negative return
- low-voltage cut-out properly managed
🚩 Red flags:
- tapped into random existing circuits
- thin cable run a long distance
- no obvious fuse near battery
6) Noise: how to avoid the “ticking pump” nightmare
A diesel heater can be very quiet — or very annoying — depending on install.
To reduce noise:
- pump should be mounted on rubber
- keep the pump away from panels that act like a speaker
- fuel line should not be tight against metal
- heater should be mounted solidly with vibration isolation where needed
If you’re buying a converted van, ask to hear it run.
7) Where should the heater be fitted?
Common locations:
- under a seat base
- inside a cabinet
- underfloor external boxes (less common in small vans)
Good installs usually prioritise:
- easy service access
- safe routing for intake/exhaust/fuel
- good airflow into the cabin
8) What to ask a converter (copy/paste)
- What heater brand/model is included and what size (2kW or 5kW)?
- Where will the heater be mounted and how is it ventilated?
- How will the exhaust and intake be routed (and heat protected)?
- How will the fuel pickup be done and where is the pump mounted?
- Is the heater on a dedicated fused circuit from the leisure battery?
- How do you reduce pump noise?
- What happens if it fails to start or smokes — what’s the support process?
9) Buying a converted van? Quick test on viewing day
- Start the heater from cold and let it run
- Check for any strong diesel fumes inside
- Listen for excessive ticking/noise
- Check it doesn’t cut out (voltage drop)
- Ask where the exhaust exits and look underneath (safely)
If it smells strongly, cuts out repeatedly, or the install looks bodged underneath, walk away.
FAQ
Is 5kW “better” than 2kW?
Not necessarily. In a small van, 2kW often runs cleaner and more efficiently. 5kW makes sense in larger vans or very cold use cases.
Can a diesel heater run off the starter battery?
It can, but it’s not recommended. Startup draw and prolonged use can flatten the starter battery. A leisure battery is the proper setup.
Why do heaters smoke?
Common reasons are poor combustion (soot), bad fuel supply, incorrect exhaust/intake routing, or repeated short-cycling.
Do I need a CO alarm?
Yes — you should have a working CO alarm in any campervan with combustion appliances.
Next steps
If you’re comparing converters, ask them to include the heater size/model and the install approach in the quote, including how they handle exhaust routing and pump noise.