Campervan Hot Water Systems Compared: Gas, 12V & 230V

Hot water is an energy problem inside a plumbing problem. The appliance must raise incoming water to a useful temperature at the chosen flow, while the tank, pump, mixer, pipe, relief and drain components stay within their ratings.

Calculate demand first

For a shower:

mixed litres = shower flow (L/min) × minutes

A four-minute shower at 4L/min uses 16L. Two people use 32L before washing-up. That figure belongs in the fresh and grey tank calculation.

For stored hot water, energy is approximately:

kWh = litres × temperature rise °C × 0.001163

Heating 10L from 15°C to 55°C is about 0.47kWh before tank and pipe losses. At an idealised 12V that represents roughly 39Ah; actual battery draw is higher because voltage, wiring and control losses exist. This is why “12V hot water” is not automatically low energy.

Compare the main options

Do not compare purchase price alone. Include flue parts, valves, mixer, pipe, electrical circuit, control panel, professional gas/fuel labour, drainage, frost equipment and the cabinetry sacrificed to service clearance.

Kettle and portable heated water

For weekenders, boil only what is needed and mix it safely in a basin. This eliminates a permanently pressurised hot circuit and winter drain points. The trade-off is manual handling and scald risk; keep boiling water stable and away from children or vehicle movement.

An induction or electric kettle still needs a correctly sized inverter or shore-power circuit. Put its actual wattage into the electrical calculator. A gas hob used for heating water must be used with the ventilation and appliance instructions; never use a cooking appliance for space heating.

Electric storage heaters

Check voltage, element wattage, recovery time and whether the vessel may be energised empty. A 500W element needs nearly an hour in an ideal calculation to add 0.47kWh, and real heat-up is longer. A 1,200W element is faster but demands about 100A from a nominal 12V battery through an inverter before losses.

Electric storage works best with shore power, abundant driving charge or a deliberately oversized electrical system. Include a thermostatic control, required relief valve and drainage exactly as specified. Never switch the element on until the tank is confirmed full.

Engine calorifiers

A calorifier transfers engine coolant heat through a coil into stored fresh water. It can be efficient on driving days, but integration with the vehicle cooling system is safety-critical. Hose specification, isolation, bleeding, coolant compatibility and vehicle-manufacturer approval matter. A coolant leak can immobilise the base vehicle.

Use specialist design and installation. Provide an alternative for stationary days and a safe temperature-mixing arrangement because stored water can become very hot.

LPG and combined appliances

Only use a heater explicitly designed and approved for leisure-vehicle installation. It requires the specified flue/terminal, combustion air, clearances, gas pressure, regulator, valves, electrical supply and commissioning. Portable unflued “camping” water heaters are not indoor campervan boilers.

Truma's Combi 4 product data shows why system matching matters: it specifies maximum pump/system pressure, water capacity, installation envelope and an optional FrostControl drain valve. Those values apply to that product, not to all heaters.

Fixed LPG work should be designed, installed and tested by an appropriately competent professional familiar with leisure vehicles. Ensure relief and drain outlets cannot discharge onto people, electrical equipment or exhaust components.

Diesel or petrol hydronic systems

Hydronic heaters circulate heated fluid through heat exchangers and can provide cabin heat and domestic hot water. They suit premium four-season builds but add pumps, expansion volume, valves, controls, electrical draw and many joints.

Separate the closed heating fluid circuit from potable water through equipment intended for that purpose. Follow fuel-system and exhaust requirements exactly. Plan servicing before enclosing the heater behind tanks or furniture.

Temperature, pressure and mixing

Every hot-side component must carry the required temperature rating. Check the pump's shut-off pressure against heater, accumulator, filter and fitting limits using the water-pump guide.

Hot stored water can scald. Use manufacturer-required thermostatic mixing and relief devices and test outlet temperature. HSE guidance for larger managed systems discusses temperature control for microbial risk and scald protection; a campervan requires appliance-specific advice, safe turnover and regular flushing rather than blindly copying building settings.

Keep hot pipe short and insulated with suitable material to reduce wait and wasted water. Avoid a long dead leg to an occasional exterior shower.

Frost protection and draining

The heater is often the most expensive freeze-sensitive component. A frost valve only protects the conditions and installation described by its manufacturer; it may require power, ambient heat or a clear drain. It does not drain every pipe automatically.

Design:

• a heater bypass if the manual permits or requires it;
• a visible drain outlet with continuous fall;
• air entry so the vessel actually empties;
• low-point drains for hot and cold branches;
• access to filters, mixers and check valves;
• a written winterisation process.

Decision worksheet

1. Do you need a fixed shower or only washing-up?
2. What mixed litres and flow are required per use?
3. What is the coldest incoming-water temperature?
4. How quickly must the system recover?
5. Which energy source is genuinely available while parked?
6. Can the pump satisfy activation flow without exceeding maximum pressure?
7. Where will flue, drains, relief and service clearance go?
8. Who will install and commission combustion/fuel work?
9. Can every water-containing part be drained before frost?
10. Does the complete system remain within payload?

Choose only after every answer is known. A modest system that can be maintained safely is better than an ambitious boiler that is permanently short of power, pressure or service access.