A calorifier is a cylinder, usually made from copper or stainless steel, that is used in some road vehicles and many boats to store and generate hot water that can be used for washing and cleaning.
The great thing that makes many calorifiers special is that they can heat water using heat from various sources. These heat sources commonly include an immersion heater, for when you have a mains power hook up, heat from a diesel heater or solid fuel stove and most importantly, waste heat from your engine. I’ll describe my own boat’s hot water system as it does all of these things.
My boat’s calorifier would be described as a ‘twin coil’ device with a 1 kilowatt immersion heater. The immersion heater is a convenient electrical heating element that provides hot water whenever we have mains shore power. The real magic though is not the immersion heater, it is the ‘twin coils’. Let me tell you what they are for and what they do.
First of all. Having twin coils is a personal choice. Calorifiers are available with either single or twin coils and if you read on you’ll see how to make the best choice for yourself. The coils themselves are just that, a simple coil of (usually) copper pipe inside the cylinder that has both ends protruding from the tank. These ends are securely fastened to the outside of the tank to prevent any leakage. The protruding pipe ends take standard plumbing fittings.
The first of these coils is designed to be connected to your engine’s cooling system in much the same way as a car’s heater is. Hot water is taken from your engine when it is running, delivered to your hot water cylinder where it circulates through the copper coil and heat from the engine’s water is transferred to the cold water inside the calorifier to be used later. This is effectively free hot water, as the engine’s excess heat would normally be discarded by the cooling system.
The second coil is there to be connected to a separate heat source, usually a multi fuel stove with back boiler, or a diesel heater made to generate hot water.
In practical terms, this is how we use our own system. In the summer while on our home mooring, we are not using either the engine or our solid fuel stove, so we use the electric immersion heater for hot water. When we take the boat out, waste heat from our engine is used to heat our 55 litre calorifier and can easily produce a tank of hot water that is sufficient for around 24 hours. The immersion heater is not used at all. In winter we spend most of our time on our home mooring, and the solid fuel stove is lit most of the time. This provides masses of hot water for both calorifier use and heating the extremities of the boat. We usually leave the immersion heater switched on in winter. We are not concerned about this as the immersion heater is thermostatically controlled and rarely comes on. This is useful if the stove goes out as it provides backup.
Simply for your information, when we bought our own unit it came complete with the immersion heater and thermostat, a pressure relief valve, an anti-scald temperature limiter, twin coils and was fully spray foam insulated. I only mention this because some products are supplied with only the internal coils, everything else is an extra cost. This can be extremely expensive so be aware.