Hot water how long before it is hot?

We have a Vetus WH 45 ( or 31) hot water heater (boiler, clarifier). The heating lament has a built in thermostat.  It is also heard by the engine when it is running.

The temperature should be kept above 60 C, so we won’t get legionairs disease.
When he engine heats up the water it gets to 80 C.

The  boiler is located on the front port side of the engine room, from there it is piped to the hull of the boat and then forward to the shower.  the pipe is 16 mm brass, and the distance from the boiler is about 3.5 – 4 Meters.  So with a diameter of 16 mm the volume of 1 meter pipe is  0.8 * 0.8 * 3.14 * 100 = >200 cm3, so 3.5 Meter is about 700 cm3.    1 liter is 1,000 cm3, so the amount of cold water which has to flow through the pipe is less than 1 liter.  Which is not a big loss.  Some boats have the hot water circulating always so there is never a ‘cold’ moment and los of hot water.    But ‘wasting’ less than a liter of water with a shower, is costing less energy than constantly having the warm water flow in a loop.

With the new Central heating unit, we wil select a model which provides CV heat and Hot water.  We could get rid of the Vetus, but why get rid of it when it is still good? there is enough space.   We have a few options.
1.   we use a T valve.  use the Vetus when warm and the CV furnace the rest of the time
2.  We plumb the Vetus > Cv furnace  > hot water line
we can start with this layout…( courtesy of Pete Milne Quo Vadis 24 M Hagenaar)


And later




Links to these parts. (TPES1/90/24)

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