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Dan222
Dan222

Posted: Mon Jan 14, 2019 11:00am

Post Subject: Back boiler

Hi, I'm new here so first up, Hello. I realise there's loads of info about back boiler systems out there, but i cant find anything that relates to what i need so could someone please help. I have a villager heron stove with back boiler (not currently installed) I have 2 radiators to 'power' there is no calorifier, no diesel heater, just plain back boiler 2 rads, on (what will be) a pumped system. Questions are, what size header tank will i need, or at least how would i work that out? I've seen these open tanks, forgive my stupidity, will the pressure get so much it'll overflow? surely thats dangerous flooding boiling water into the boat? If i fitted a pressure release pipe directly behind fire, could that be simply a copper pipe running straight up through the roof? Not sure why, but this is really confusing me when i'm not sure it should. haha. Thanks for any help received. Cheers, Dan

Tony-B
Tony-B

Posted: Mon Jan 14, 2019 3:16pm

Post Subject: Back boiler

Sorry but your first "mistake" is deciding on a pumped system with just two rads and a stove. With non-termostatically controlled solid fuel stoves gravity is a far safer and in many cases a better option because the hotter the stove gets the faster the water will circulate (within reason) and it requires no electricity to run so it can run 24/7 without depleting your batteries. If you do fit a pumped system (which I do not advise) then make sure you have both a pipe-stat AND a manual override switch to control the pump. If the pump or electricity supply fails you will end up with boiling water and steam spewing out of the header tank. I have no idea why you are talking about a pressure relief valve. Although they are vital on sealed, pressured systems they are no required on open vented boat systems PROVIDING the feed and expansion pipes from the expansion tank to the system pipework are 15mm or larger. Pascals law says that pressure is equal throughout a system so with an open vent it can not pressurise as long as the feed & expansion pipes do not restrict flow. No one can answer your question about the size of expansion tank until you say the volume of water & antifreeze there will be in your system but something like this https://www.midlandchandlers.co.uk/store/categor y/1467/product/tt-006.aspx will probably be adequate without more info from you. You can drill the sides or back to fit a vent pipe into it or to direct expanding water through the cabins side if the possibility of steam and boiling water worries you. Wherever you vent an open system the vent outlet must be higher than the header tank level so you could vent through the roof or towards the top of the cabin side. It is not pressure you need to worry about but expansion caused by heating and if it does boil the volumes of stem and possibly spitting hot water drops but the tank I linked to has a cover that will stop much of any water spatter.

Dan222
Dan222

Posted: Mon Jan 14, 2019 4:24pm

Post Subject: Back boiler

Thanks for the response, So, the main reason for a pumped system is i am not confident in getting a gravity system correct. I dont know a huge amount as to how it works, but from what i gather you have to angle pipework? also it cant be tucked down at floor level? The pump will be controlled by a thermostsat, and i'm not so worried about electrics as i'm hooked up on shore all of my 12v things are run through a transformer. I'm talking about a pressure relief, because as stated above have read loads of info about the systems and that has come up a lot, i aslo dont like the idea of having hot water or any water for that matter spewing out anywhere inside, to me it seems a bit daft to have an unsecure lid on a tank ready to spill out all the water. By pressure i mean to say expansion, in a similar sense of boiling water in a tight space and boiling over. Cheers

Tony-B
Tony-B

Posted: Mon Jan 14, 2019 5:58pm

Post Subject: Back boiler

To a degree much depends on where the stove is and how the boat trims. If the boat trims stern down, as most do, and if the stove is at the back then all you normally need is a vertical leg from the top back boiler connection that then bends (not elbow if possible) and runs tight under the gunwale forwards. This pipe needs to be in at least 28mm or larger. It runs to the far end of the boat/heating layout, bends down and then back at close to floor level back to the stove. The rads can be piped in 15mm copper. ON my boat both rad connections came from the bottom pipe but many fit a feed into the top of the rad in the top pipe and the return to the bottom. NO rad valves are typically used in a gravity system. I can't think why low level pipework can not be accommodated at or close to floor level on a typical canal boat. After all the pumped system will require low level pipes and connections. Any boiling will be in the boiler, its only steam and hot water moving up the expansion pipe into the tank. In any case the tank I linked to is made of plastic so 5 minutes with a drill and two self tapping screws will secure the lid but it will not make it water tight. That should not matter as long as you fit a high level vent towards the top of the tank running through the cabin side. But its your boat and your choice, nothing else to say. Don't confuse closed & pressurised systems or domestic (house) systems with open systems on boats.

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