Originally Posted by Shaneesprit
Has anyone got any tips or advice / ideas
I have a small CAT 25ft 4/6 berth
Need to install heating and hot water.
So the issues
Cost / Space / weight
Diesel like the Engine
- easy for Hot air heating - not easy for Hot water
Gas like the stove - Easy for hot water - Not easy for heating
But I want both but I am only fitting one system.
Whatís your solution?
My solution may or may not help, depending on your definition of what is acceptable weight.
Based on some great design work
by CF Member
ColdEh (John), I am heating water using a diesel water heater
, and tapping into that heated water for both my hot fresh water and boat
Now John advocates a pretty large capacity system to ensure the diesel furnace operates efficiently and with a minimum of maintenance
, but I guess his design could be made lighter if you were willing to put up with a bit less efficiency and the chance of more maintenance
In short, John's design heats a buffer tank of water which is treated with an anti-corrosion agent. This is pumped around the boat
for hydronic heating. Inside the buffer tank is a coil of copper pipe that you use to heat your fresh water on demand by pumping it through the coil on the way to the galley
I have built my tank and heat exchanger
and they are working just as John's predicted. I have a 6 litre/minute flow for shower
temperature water (43 degrees C) with the buffer tank only raised to 55 degrees C. (When I have insulated the tank I will see how that rate of flow can be increased with an increase in tank temperature, but as it is it is more than adequate.)
I have a trio of commercial
van heaters I salvaged from some Series 3 Toyota Hiace vans and I pump
the buffer water through those to provide heating for the boat. Needless to say, they work
perfectly, since from their point of view the whole thing is no different to what they would get from the car engine, except the pump I am using is a bit more effective.
The downside is that the whole lot, when full of buffer liquid, is close to 100 kg. This is because I managed to squeeze 83 litres into the buffer tank to make the system more thermo-stable then there's at least 10 litres in the hoses the feed the various areas of the boat plus the furnace itself and the van heaters (they are actually very light.)
But I do think you could take the general principals and maybe trim them down by:
(a) using a smaller buffer tank, around 20 litres feels workable, given the reaction time of the diesel furnace.
(b) using a plate style heat exchanger
to extract heat for your fresh water.
(c) keeping the number of heaters and the pipe runs to them to a minimum.
Maybe 40 kg all up?
A 25 foot cat probably has the same volume of interior
as what... a 30 foot mono. One heater would probably cope.
Here's a link to John's thread:
And here's a schematic of the system as I am building mine, which is subtly different in the way it keeps the boat heating circuit completely independent of the furnace circuit. I do this because my boat will spend most of its life in a very warm climate. (I hope).