When you’re gearing up for off-grid travel or tackling chilly mornings on the road, a diesel heater can be one of the smartest upgrades for your caravan. But choosing the right size isn’t just about plugging something in and hoping for the best. You need to think about internal volume, insulation, airflow, power draw, and where you’re headed.
If you’ve been shopping for caravans in Heatherbrae, odds are you’ve come across options with or without built-in heating. Whether you’re retrofitting an older van or speccing out a new model, understanding diesel heater sizing will help you stay warm — without wasting fuel or overloading your system.
Why Diesel Heaters Are a Popular Choice
Diesel heaters are a favourite among Aussie travellers for a few good reasons. They’re efficient, reliable, and capable of running off the same fuel as your tow vehicle. You don’t need 240V power, and most models sip just a fraction of a litre per hour.
For those who like free camping or venturing off-grid, diesel heaters provide warmth without draining your battery bank or relying on noisy generators. Plus, they’re safer than portable gas heaters and don’t cause condensation like propane heaters can.
How Diesel Heaters Work
A diesel heater draws in air from outside your van, warms it via a combustion process, and then circulates the heated air through ducts into the interior. The combustion happens in a sealed chamber, keeping harmful gases out of your living space. Exhaust exits through a pipe mounted under the van.
You’ll need a fuel tank (some vans tap into the tow vehicle’s tank), a small 12V power supply, and appropriate ducting. Most modern models are thermostatically controlled, so once the desired temp is reached, the heater ticks over at low output to maintain comfort.
The Two Most Common Sizes: 2kW vs 5kW
The vast majority of caravan diesel heaters fall into two categories:
- 2kW models — Ideal for small to mid-sized vans (up to ~20ft)
- 5kW models — Better suited to large vans, toy haulers, motorhomes, or multi-room setups
Most Aussie caravans under 22 feet will do perfectly fine with a 2kW diesel heater. It’ll heat the space efficiently without being overkill. A 5kW model may be too powerful for small vans and could short-cycle or make the interior too hot too fast.
Matching Heater Size to Van Length
Use this as a rough guide:
| Caravan Length | Suggested Heater Size |
| Under 18 ft | 2kW |
| 18–22 ft | 2kW (insulated) or 5kW (thin walls or cold regions) |
| 22–26 ft | 5kW |
| Over 26 ft | 5kW+ or dual-zone setup |
Don’t just look at square footage — also consider ceiling height, wall insulation, and whether you’ll be heating one area or multiple rooms.
Climate Makes a Big Difference
If you’re heading into alpine regions or the Victorian high country, lean toward the 5kW side. Even a well-insulated van loses heat faster in sub-zero temps. On the other hand, if your travels keep you along the east coast or warmer areas, a 2kW heater is almost always enough.
Insulation Matters
A van with composite walls, insulated flooring, and double-glazed windows holds heat far better than a vintage rig with aluminium walls and gaps galore. Better insulation = less heater output required. Before going for a larger heater, consider improving insulation first — it could allow you to stick with a smaller, quieter unit.
Fuel & Power Draw
A typical 2kW diesel heater uses around 0.2–0.3L of fuel per hour and draws 10–30W of 12V power, mostly during startup. A 5kW model burns more fuel (0.4–0.6L/hr) and pulls more current.
Make sure your battery setup can handle the startup draw — especially if you’re running solar-only power. Lithium batteries handle this better than AGMs.
Can You Use Two Heaters Instead of One?
Yes — in large or multi-room caravans, some people opt for two smaller heaters instead of one big one. This gives you better zone control and avoids overheating small areas. It’s also handy if different sleepers have different temperature preferences.
FAQs
1) Can a 2kW Diesel Heater Warm an Entire Caravan?
Yes — in most cases, a 2kW diesel heater is powerful enough to warm a standard single-room caravan (under 20 feet) with ease. These units are designed for small spaces and are particularly efficient when the caravan is well insulated. The 2kW size balances performance and fuel efficiency — it delivers enough warmth without short cycling or overheating the cabin. If your van has modern composite walls, thermal blinds, or additional insulation, a 2kW model will keep things toasty even in chilly NSW winter mornings. The only time you might find it lacking is in high-altitude conditions or if you’re trying to heat a large open-plan space. For anything up to about 22 feet, though, 2kW is usually the sweet spot. It’s also quieter than larger models, which can make a big difference when trying to sleep on a cold night.
2) What If I Choose a Heater That’s Too Powerful?
Going too big might sound smart — but it can actually backfire. A 5kW heater in a small van will often short cycle. That means it heats the space too quickly, shuts off, then fires up again shortly after. This frequent on-off cycling wears out components faster, uses more battery power during startups, and may lead to an uncomfortable, inconsistent temperature. Overpowered units are also noisier and more expensive to run in terms of fuel. Unless you’re heating a really large van or plan on staying in below-freezing temps for long periods, a smaller unit will offer smoother, more reliable heating. Plus, overkill in a confined space can make the air too dry or create hot spots near vents. Always size your heater to your van’s actual heat loss profile — not just its square footage.
3) Are Diesel Heaters Safe to Use Overnight?
Yes — when professionally installed and maintained, diesel heaters are safe to run overnight. These systems are sealed combustion units, meaning the combustion chamber is isolated from the cabin air. Exhaust gases are expelled outside, and only clean, warmed air is blown inside. However, proper installation is critical. This includes correct placement of the exhaust pipe, secure fuel lines, and fireproof mounting points. Most quality units include built-in safety sensors like flame-out detection, overheat protection, and automatic shutdown. As with any heating appliance, regular servicing is important. Clean the combustion chamber, check the glow plug, and ensure no carbon build-up or leaks. Also, make sure your van has proper ventilation. If installed incorrectly, a diesel heater can pose fire or fume risks — but done right, they’re one of the safest options for off-grid caravan heating.
4) Can I Install a Diesel Heater Myself?
Technically yes — but it depends on your confidence and experience with 12V systems and vehicle modifications. Installing a diesel heater involves cutting a hole through your van floor for the exhaust, mounting the combustion chamber securely, running ducting, wiring up to your battery system, and possibly installing a separate fuel tank. Mistakes here can lead to fire hazards, exhaust leaks, or flat batteries. That’s why many caravan owners choose professional installation, especially for insurance and compliance reasons. That said, there are excellent kits on the market and detailed install guides available for capable DIYers. Just make sure you follow all manufacturer guidelines, use proper heatproof materials, and take your time. And if you’re in doubt — call a licensed installer. The upfront cost often pays for itself in peace of mind and system longevity.
5) What’s the Cost of Buying and Installing a Diesel Heater?
Prices for diesel heaters vary widely depending on brand and size. Entry-level 2kW units from Chinese manufacturers can be found for around $150–$250, while reputable brands like Webasto and Eberspacher may cost $1,200–$2,000. Installation, if done professionally, typically ranges from $300 to $700 depending on complexity. Most people budget around $1,000 for a good quality unit fully installed. Don’t forget to factor in extras like fuel lines, mounting brackets, ducting, and thermostats. It’s also worth noting that higher-end heaters tend to be quieter, more reliable, and backed by better warranties. If you’re travelling often, especially in colder climates, investing in a trusted brand can prevent headaches down the track. For occasional use or warm-weather touring, a budget model may suffice.
Speak With the Local Experts at 7th Street Caravans
Heating your van is just one piece of the puzzle. Whether you’re exploring off-grid upgrades or looking to spec out a new van, it helps to talk to people who know caravans inside out. At 7th Street Caravans, we’ve helped hundreds of Aussie travellers choose setups that suit their lifestyle — and the weather they’re travelling in. From heater size to battery compatibility and ducting tips, our team can walk you through what works and why.
Start your journey with confidence — visit 7th Street Caravans or give our team a call on 02 4012 6009 for friendly, local advice.