Your Caravan’s Diesel Hot Water System

Diesel hot water is the premium option increasingly found in mid-range and high-end caravans. It runs from the tow vehicle’s diesel tank (or a separate small diesel tank in the caravan), uses minimal 12V power, and often provides both hot water and space heating from a single integrated unit. For off-grid travellers with a diesel tow vehicle, it’s arguably the most convenient hot water solution available.

How It Works

A diesel burner combusts a small amount of diesel fuel to heat either water directly (in a heat exchanger) or a coolant that then heats both water and air for space heating. The most popular integrated system is the Truma Combi D, which provides hot water and space heating from one unit. Diesel consumption is low: typically 0.1 to 0.3 litres per hour, making it very economical to run.

The system draws a small amount of 12V power for the fuel pump, fan, and control electronics (typically 1 to 3A), which is easily managed by a standard battery and solar setup.

Advantages

True off-grid capability: Works without mains power and without consuming LPG. Ideal for extended free camping.

Fuel availability: If your tow vehicle is diesel, you’re carrying the fuel anyway. No separate gas bottles to manage for hot water.

Dual function: Integrated systems provide both hot water and space heating, eliminating the need for separate systems.

Efficiency: Diesel produces more heat per litre than LPG. Running costs are lower than gas for equivalent hot water production.

Common Systems

Truma Combi D6 (Most Popular Integrated, $3,000 to $4,000 installed): The benchmark diesel combo unit for Australian caravans. Provides both hot water (10-litre tank, heats in about 20 minutes) and space heating through ducted vents. Controlled via the Truma CP Plus digital panel or the Truma iNet app from your phone. Very well-supported in Australia with a strong dealer network. The D6 is the 6kW version; the D4 (4kW, $2,500 to $3,500) suits smaller vans.

Webasto Dual Top Evo (Premium Alternative, $3,500 to $5,000 installed): A high-end diesel combo unit that provides both hot water and cabin heating. Slightly more powerful than the Truma D6 and known for robust build quality. Less common in Australian caravans than the Truma but well-established in the European and marine markets.

Planar/Autoterm Diesel Hot Water (Budget Diesel, $1,500 to $2,500 installed): Russian/Chinese-made diesel units increasingly popular as a more affordable alternative to Truma and Webasto. The Autoterm Flow 5D provides diesel hot water without the space heating combo. Build quality is adequate but not at the European level. Parts support in Australia is growing but not yet as comprehensive as Truma.

DIY diesel hot water via heater: Some travellers add a standalone Chinese diesel heater ($200 to $500) and route the hot air past a water heat exchanger to create a DIY diesel hot water system. This is a budget approach that works but requires mechanical skill and careful installation. Not recommended unless you’re confident with plumbing and electrics.

Considerations

Cost: Diesel hot water systems are more expensive to buy and install ($2,000 to $4,000+ for a quality integrated system). This is usually factory-fitted or installed by a specialist.

Noise: The burner and fan produce a low hum, noticeable in a quiet bush camp. Modern units are much quieter than older designs, but they’re not silent.

Maintenance: Diesel burners need periodic servicing (clean the burner, check the fuel lines). Running the system regularly prevents carbon buildup. If the van sits unused for long periods, run the diesel heater for 15 to 20 minutes monthly.

Petrol tow vehicle: If your tow vehicle runs petrol, you’ll need a separate diesel tank in the caravan (typically 10 to 20 litres). This adds complexity and weight but is still viable.