Having a reliable supply of hot water is one of the essential comforts that transforms a vessel into a true home on the water. For many boaters on the UK’s inland waterways, the most effective way to achieve this is through a specialised marine water heater that captures heat that would otherwise be wasted. These systems are elegantly simple, converting your engine’s running time into free hot water for showers, cleaning, and galley use.
How a Marine Calorifier Recycles Energy
The genius of this system lies in its ability to recycle heat from your boat’s engine cooling circuit. Instead of letting that thermal energy vanish overboard, it is diverted through a sealed heat exchanger coil inside a heavily insulated tank.
- Heat Transfer: Hot coolant from the engine flows through the internal coil, radiating heat into the fresh water stored in the tank.
- Separation: The engine coolant and your domestic fresh water never mix; they are kept in completely separate, sealed circuits.
- Insulation: High-quality polyurethane foam acts like a giant thermos flask, keeping the stored water hot for many hours after the engine has been switched off.
Single-Coil vs. Twin-Coil Systems
When selecting the right unit for your boat, the decision usually comes down to how many heat sources you want to utilise.
The Single-Coil Solution
A single-coil unit is the standard choice for continuous cruisers. It features one internal coil connected directly to the engine. It is highly efficient and straightforward to install, providing free hot water every time you are on the move.
The Flexibility of Twin-Coils
A twin-coil calorifier includes a second, independent heat exchanger. This allows you to connect an additional heat source, such as a diesel-fired water heater or a boat backboiler system. This setup is ideal for liveaboards who spend time moored up, as it provides hot water without needing to run the main engine.
Choosing the Correct Capacity
Selecting the right size tank is a balancing act between your crew’s needs and the available space in your engine room or locker.
| Number of People | Recommended Capacity | Typical Usage Profile |
| 1-2 | 15-25 Litres | Weekend trips and solo cruising. |
| 3-4 | 30-50 Litres | Regular family use and daily showers. |
| 4+ | 50-75+ Litres | Full-time liveaboards or larger crews. |
Safety, Regulatory, and Professional Installation
To ensure your system is safe and compliant with the Boat Safety Scheme (BSS), several key components must be correctly fitted. Every installation we perform is designed to meet the guidelines set by the Canal & River Trust (CRT) and is handled by OFTEC-trained specialists.
- Pressure Release Valve (PRV): This is a non-negotiable safety device that prevents the tank from over-pressurising as the water expands.
- Accumulator Tanks: These act as a pressure buffer, ensuring a smooth flow of water and protecting your pump from excessive wear.
- Winterisation: It is critical to drain the tank during the winter to prevent frost damage, which can split even the toughest stainless steel tanks.
If you need assistance with your system, our Boat Plumbing Services team can help with everything from new installations to emergency repairs.