Calorifiers, Expansion Tanks & Accumulators



The blue calorifier and red expansion tank shown above are from my own boat. They are both produced by the British company Surejust Ltd. We've now had the unit for almost five years and it remains faultless.

The beauty of the model above, is that there are three ways to heat the 55 litres of water this one contains. (There are other sizes available.) It does come supplied with a 1KW immersion heater for when you are on shore power, but importantly it also has a coil that you can connect to your (water cooled) engine and another coil that can be connect to another heat source like a solid fuel stove that has a back boiler, or some types of diesel heating.

Part of the attraction of this type of calorifier tank is the convenience of electricity when available, free hot water from your engine whilst cruising and winter heat from your stove.

The expansion tank pictured is also important because it reduces the wear on your water pump by storing water, at pump pressure, and by doing so it reduces the number of times the pump has to run from a 'standing' start. The cold water version of the expansion tank is often called an 'accumulator', though both tanks effectively do the same job.

Don't waste your time or money by purchasing a very small expansion tank. The one in the picture above is a 5 litre one. From my own experience I would say that this is probably as small as you should go. Bigger would be better.

To set up your expansion / accumulator tank you will need an air pump and an air pressure gauge. I use a small electrical car tyre pump that has a built in pressure gauge. You will also need to know your water pump's operating pressure. My Johnson pump operates at 42PSI. Before you install your tank you should attach your pump/gauge and adjust the tank's internal pressure to HALF of your water pump pressure (21 PSI in my case). This way, when it's all connected up, your expansion tank will be completely full just as your water pump switch reaches its cut off pressure. Simple really.

Here are some links for you. I will just point out that I bought from Surejust (also known as Surecal) because they were the best price and were supplied complete with the adjustable immersion heater, the pressure relief valve, and very importantantly the anti-scald valve. Some other tanks are not complete and the parts mentioned are expensive when purchased separately. Okay back to the links.