New WaterHeater needed (Now updated)

Hi,

In practice there really isn’t much excess space.

Edited by Rock - 12 October 2024 at 09:57

When I first fitted the webasto water heater I was using the original 20L hot water tank. Initially I fitted a shuttle valve T joint as the original tank only had a single heat exchange coil. This allowed me to have the engine and the heater connected and enabled either the engine or the webasto to heat the water. I had a major problem with this setup as the heater kept shutting down early before fully heating the water because the coil in the Isotherm tank had far to small a heat exchange area that the heater beat the heat loss in the circuit and shut down early. To overcome early shut down I removed the shuttle in the T piece and allowed the heater to heat the engine as well. This gave sufficient area/ volume for it to dump the heat it was making. Shortly afterwards the Isotherm cylinder started to leak (it’s an extremely poor design which is only made to last slightly longer than the warranty period, it even has an internal anode to ensure this). I decided to replace it with a system that was properly designed for its location in the boat, to have two separate coils each capable of transferring 8Kw of heat and to give me as much additional hot water capacity as possible. To give me as much space for the tank I cut out the bottom of the glass fibre recess that the standard tank fits in, this gave me additional depth and allowed me to have a tank made with a 29L capacity giving an extra 45% of hot water. I decided to do away with the over pressure valve as I viewed this as a future failure point, but in doing this I had to fit a pressure bottle in the system. This is an absolute must if the pressure relief valve is done away with, it’s also a really useful thing to add to the water system to prevent over pressurisation when the water is heated and to maximise the life of the water pump. With the base of the moulding cut away the new hot water tank sits on the hull skin and it is held firmly in place by using pu foam around it in the cavity. To ensure the pu foam didn’t bond to the hull plastic sheet is placed down and taped to the side of the recess the tank sits in when this is done connect the plumbing, test and then pu foam around the edges to secure in place (use extremely small amount of foam, let it cure and if required add more. It’s a nightmare to clear up if you use too much).

Simon - very useful - we did consider cutting out the bottom of the original locker. But we decided it was easier to just move it aft and put it in the garage.