Posted: Mon Dec 06, 2010 1:00pm

I have spent much time contemplating how to heat my recently purchased 70ft widebeam. I've considered various combinations of gas/oil/solid fuel systems. I'm a live-aboard and want to keep things as simple as possible. My conclusion is to install a large solid fuel stove with backboiler to heat the six existing radiators connected to a large calorifier for hot water. I've narrowed the search down to the Morso Dove and the Stovax Stockton 8HB. I was hoping that this could be a gravity fed system but the guys at the boatyard have said there is no way as the pipes would have to travel half way around the boat and back. If I must have an electric pump for circulating the heat, I would like it to be 12v but, again, the engineer has said I will have to use a 240v pump. Is this correct?? How do I work out what I need? The existing copper pipes are only 15mm. Would replacing the pipes help or shall I leave well alone and just get a 240v pump and inverter?

Posted: Mon Dec 06, 2010 4:21pm

Dear Lisa, I think you need to take other advice (as you have on the newsgroup) because I had gravity circulation on a 54 ft boat and Waterways world did it (I think) on a longer one. ON both boats the radiators were down one side and I suppose that if you have organised things so radiators are on both sides of the boat gravity circulation would be difficult. It will need large bore pipes (28mm plus) to work and to be absolutely sure the hot pipe would have to run at close to roof level rather than under the gunwale. However it could well work by gravity with the hot pipe under gunwale, especially if the stove is at the back so the hot pipe run gradually rises as it runs forward with the boat's trim, but it would be a lot of work just to find out you would need to raise the pipe to roof level. There are several 12V central heating pumps available, the one with a very low power consumption is the Bolin pump but they cost over £100. I really wonder about your boatyard because they should know about Boin pumps and the way to run gravity systems in large bore pipes. Did you give them the impression you wanted to retain the 15mm pipe? I even used 22mm pipes for the three radiators on my Alde system. It might be that the Bolin pump is not large enough to supply six radiators. Back to the gravity system. Stove at one end of the boat, high level large bore pipe from top stove connection to the furthest away radiator. Low level large bore pipe back from there to lower stove connection. The radiators either Td off the lower pipe(both ends of them) or a T in the top pipe to the top of each radiator and the a pipe from the bottom of the radiator to a T in the lower pipes. These T pipes can be in 15mm. You may also want to fit a manual radiator valve to one end to adjust the flow rate through the radiator. You will also need a header tank above the top pipe and a way of venting air from the system at the highest point in the main pipework. To answer the question I am afraid depends upon how much you are willing to pay. I suspect the cheapest and by far the easiest option would be the mains pump and inverter (but goodness knows what that will do to your batteries) but I am sure you could get a gravity system working as long as you are prepared to search around for someone who knows what they are doing and you are willing to pay. Note what the other Tony told you on the newsgroup. Tony Brooks

Posted: Tue Dec 07, 2010 9:55am

Thanks Tony. Yes, money and time is also an issue as we were hoping to move on to the boat in the New Year! I think I may have to abandon the gravity idea as the existing wood stove is half way down the boat and radiators are on both sides of the boat. So now I need to work out what sort of pump will do what we need and I'm not sure where to start. I can't seem to find any information about flow rates for the Morso Dove boiler. I'll persevere...

Posted: Tue Dec 07, 2010 2:05pm

Boilers/stoves are rated in kW or BTU which are both measurements of the heat output. It has nothing to do with flow. You have to ensure the flow through the system and the temperature difference across the radiators is sufficient to dissipate all the heat the stove produces otherwise the water will boil. I am afraid that you are now firmly into the province of heating engineers and a bit outside mine so I would suggest that you find a central heating engineer or plumber who will work the flow rate out for you. However they may well need to know a value for the insulation of your boat so they can calculate the amount of heat lost from the boat. I have managed to find some figures for the Bolin pump and I reproduce them below. I rather suspect it may be too small for a larger stove. It also looks as if it will not be happy on 15mm pipe. PUMP INFO 400 Litres per hour, 6.67 Litres per Min, 0.11 Litres per Sec. Must be fitted on 22mm pipe work (flow & return). The Bolin pump will circulate up to 5kW of heat.