Posted: Mon Jul 20, 2009 1:07pm

Hi Tony, I'm looking to fit a back bolier to my Aarrow Becton BUnny 5 multifuel stove. I've made some enquires and been told a 1.6kW stainless steel one is available. Can you tell me what I might be able to feed from this? I was hoping the second coil on a calorifier to supply hot water, and also a radiator or two. If this is too much do you know if bigger back boilers are available for this stove? Also would this system require some kind of temperature activated pump to move the water round, and would the backbolier need a blow off valve for when water is static in the system, but the stove is still on? Cheers, Ben

Posted: Mon Jul 20, 2009 5:50pm

Dear Ben, first of all the amount of energy required to do a particular job is related to the temperature you wish to achieve (this also has an input into radiator sizes), the window area and if single or double glazed and the insulating (U) value of your boat. Only after you have all this information, including radiator size) can a central heating engineer calculate the answer you want. I suspect if the boat is insulated with expanded polystyrene or better 1.6Kw will do what you ask, however the radiators may not reach maximum temperature until the calorifier is hot and the question of the cabin temperature that can be reached is also open. You must direct questions about the availability of larger boilers to the stove manufacturer. There are two ways to pipe up your system. Gravity that uses a high and a low level large diameter pipe run or pumped which uses two small low level pipe runs plus a pump. You have to decide which system bets meets your requirements. You must NEVER have the stove alight without a method of dumping the heat so you must have at least one radiator permanently connected to the stove so heat can be dumped when the stove is alight. Over and above this you should have at least one vent pipe so water & steam can be vented from the system if it boils. You will also need a header tank to allow the water in the system to expand when heated and contract when cooled. If you choose a pumped system I advise a manual switch for normal use and a thermostatic one on the boiler outlet pipe to ensure the pump runs if the stove is lit with the pump turned off. Tony Brooks