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boat heating

As the temperature starts to fall we will be needing the heating back on. Ive got a pretty good system. Only complaint is central heating does not work off engine heat but hot water produced both from engine and central heating. My biggest gripe is because the calorifier is at the back of the boat and sink, basins and shower at the front you have t orun off so much water before it starts running hot. was thinking of fitting one of these,https://www.aquahot.co.uk/hyco-sf10k-speedflow-premier-undersink-unvented-water-heater-10l#reviews, 1.2kW of course. By the sink but on the hot line rather than cold. I appreciate it will not be any good for a shower but be nice not emptying the calorifier just to fill the sink. Any thoughts or recommendations of how others have got around this concern? I do not what to install gas on the boat. Thanks

Asked by: John Lawson  | 1.43pm, Friday 2 September


WW says:

If you have say 20 metres of hot water pipework running from the calorifier to the sink, and that is 15mm plumbing, then the volume of water contained in that pipework is 3.5 litres. Although it seems a lot of water, it is not much compared to the content of the pipework. Insulating the hot water pipework from the calorifier can reduced radiated heat loss for the system, and many boatbuilder do this. However, fitting an additional water heater inline with the calorifier is probably excessive. It is often poor practice to pass hot water through two heating devices (which is to avoid scalding water by double-heating) though as the heater unit would be thermostatically controlled, this should not happen.
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Also, the hot unvented hot water systems you mention sometimes are not designed for water systems at the pressures that some pumps can produce- you would need to check with the instructions.
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If you were plugged into a 230V source, then having the water heater as an additional heater source, with a switchable supply, would be a good idea. However, if you are heating the water tank from a invertter (from a 12 or 24V source) then it would take a large amount of battery power- which would need to be replaced by running the engine (which, of course, would be heating the water...!)
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Turning the system into a district hot water system, as suggest my Martin, is possible, but very unusual. You would also need to fit a return to the calorifier in the cold water feed. This may have addition complications, and, if one is not already fitted, would certainly require an expansion vessel to be fitted in the water line (this is good practice anyway- and routinely ignored- as it prevent stress damage to the calorifier). See recent WW articles of water systems for more details on how to achieve this.
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The short answer is that, bar insulating the pipework, most boaters live with this. Usually less water runoff happens waiting for the hot water to come through on a boat, than it does in any house ashore!

Mark Langley  | 10.35AM, Friday 9 September

If you install it under the sink, I would ensure that it is hard wired into an isolation switch that is away from the sink (rather than just a plug into a socket- this might be a condition of the installation instructions). Also, ensure that continuity of earth is present in the system, now you are adding a 230V appliance to the water system- any metal pipework/sinks must be bonded to the hull and the 230V system earth, to avoid potential for electric shocks if anything goes wrong. Also, check the maximum operating pressure for the hot water unit and adjust the system pressure is appropriate. Fitting a non-return valve to the feed supply might be useful as well.

Mark Langley  | 12.31PM, Friday 9 September

If you ran a district system on convection alone, you would run the risk of "dead spots" with a severe risk of legionella forming, which should be avoided at all costs. One reason district systems are not installed is the risk of microbial contamination- they have to be kept at 65 to 70 degrees celcius, which could be challenging in a boat used infrequently. Large ships use this system, but they have to meet stringent requirements for system design and operating. You might find that, if you fitted such a system, it would be flagged up as a problem by a surveyor if and when you come to sell the boat to a potential new buyer.

Mark Langley  | 12.34PM, Friday 9 September


Readers say:

You could run another pipe from the sinks, shower etc, back to the calorifier and fit a small circulating pump, but you would need to insulate it. It seems a shame to use electricity when you have a free source of heat. I realise you may not be able to run extra pipework but it's just a thought. The pump would only need to be run when the engine was on.

Martin Ross  | 5.19PM, Thursday 8 September

Thanks for the reply's. Martin's suggestion is certainly an interesting one. Maybe with a height difference between supply and return a pump may not be necessary. The hot and cold water may set up sufficient of its own circulation? WW. Must confess I didnt do the maths and you are right 3.5 litres is certainly a lot less than it seems when you are stood waiting, listening to the pump. Although it does add up if you are dumping 3.5 litres every time. I will be insulating all of the pipes, cold and hot as I know currently non are. Just out of interest I have ordered one of those heaters as often when we are just on the boat for the weekend or even the day it doesnt seem worth heating a full tank. I know boiling a kettle would be just as effective but we can never be bothered to wait for it boiling so we have been managing with cold water most of the time. I dont intend using it off grid as we will be producing hot water any way. Thanks again for your thoughts and taking the time to reply.

John Lawson  | 11.55AM, Friday 9 September

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