central heating pump

[Tracy D'arth]

Back boiler flow [top] pipe [22mm minimum] up to under the gunwale, along forward with 15mm pipes dropping to the top connection of each radiator and on to the bottom of the expansion tank, [ where you can fill the system, ]  [what you have as overflow,]  in 15mm which must be higher.

Return from bottom of each radiator along floor into 22mm again back to the return [lower] on the boiler. Radiators most efficient with top and bottom connections diagonally across the radiators.

Golden rule, flow pipe must rise away, all the way, form the boiler and return must fall towards the boiler. Easy with your layout because the bow of most boats is higher anyway.

Drain tap at the lowest point.

 

No pump, no electrics, safe providing the radiators a re big enough to take the output of the boiler. 

If calorifier is required as well, same 22mm pipes to boiler from calorifier with a vent valve at the high point on the calorifier.

Edited June 9, 2020 by Tracy D'arth
added more text

[Tony Brooks]

and in my opinion 28mm or lartger would be  better circulation wise. May be fit a high level air vent pipe to the highest point in the main pipework.

[Tracy D'arth]

3 hours ago, Tony Brooks said:

and in my opinion 28mm or lartger would be  better circulation wise. May be fit a high level air vent pipe to the highest point in the main pipework.

Going off the accepted wisdom and practice I would agree that 28mm is the prefered size for gravity systems but from experience I am convinced that 22mm main circulation pipes correctly installed are adequate for the distances in a 58ft boat. 

The cost of 28mm pipe and fittings is considerably more than 22mm, especially in copper, and in plastic the fittings are large and cumbersome.

I have installed quite a few this way and provided there are no air pockets in the pipework due to improper falls and rises they have never suffered overheating or boiling when heavily fired.

With plastic pipes they have to be supported throughout their length otherwise they sag and case air locks. This is easy to achieve with the return, being on the floor, but the flow needs to be on a batten under the gunwale.

I much prefer copper, its easier to get straight and off a solid fuel boiler I have my doubts about coping with the considerable expansion of plastic. As it is a seperate system it can have antifreeze added so copper is better all round.

Certainly the first 2 metres from the boiler must be copper or steel.

My present system is 22mm off the Squirrel to the calorifier with the heating circuit in 15mm to 3 concealed radiators with thermostatic valves going aft and a 15mm circuit of just pipe going forwards to loop around the rear of the bow water tank to stop condensation and to heat the front of the saloon.

This 15mm circuit is some 40 feet in length and pulls on gravity extremely well.

[Deano1988]

22 hours ago, Tracy D'arth said:

Back boiler flow [top] pipe [22mm minimum] up to under the gunwale, along forward with 15mm pipes dropping to the top connection of each radiator and on to the bottom of the expansion tank, [ where you can fill the system, ]  [what you have as overflow,]  in 15mm which must be higher.

Return from bottom of each radiator along floor into 22mm again back to the return [lower] on the boiler. Radiators most efficient with top and bottom connections diagonally across the radiators.

Golden rule, flow pipe must rise away, all the way, form the boiler and return must fall towards the boiler. Easy with your layout because the bow of most boats is higher anyway.

Drain tap at the lowest point.

 

No pump, no electrics, safe providing the radiators a re big enough to take the output of the boiler. 

If calorifier is required as well, same 22mm pipes to boiler from calorifier with a vent valve at the high point on the calorifier.

Thanks for this it's starting to make sense.

 

(Sorry for the drawings but just find it easier tk get my head around)

 

Have I got your explanation right?

From the drain tap it will have to go up to the stove is this correct? 

 

Thanks dean 

[Tracy D'arth]

Back boiler flow [top] pipe [22mm minimum] up to under the gunwale, along forward with 15mm pipes dropping to the top connection of each radiator and on to the bottom of the expansion tank, [ where you can fill the system, ]  [what you have as overflow,]  in 15mm which must be higher.

Return from bottom of each radiator along floor into 22mm again back to the return [lower] on the boiler. Radiators most efficient with top and bottom connections diagonally across the radiators.

Golden rule, flow pipe must rise away, all the way, form the boiler and return must fall towards the boiler. Easy with your layout because the bow of most boats is higher anyway.

Drain tap at the lowest point.

25 minutes ago, Deano1988 said:

Thanks for this it's starting to make sense.

 

(Sorry for the drawings but just find it easier tk get my head around)

 

Have I got your explanation right?

From the drain tap it will have to go up to the stove is this correct? 

 

Thanks dean 

  Yes. that is correct, up to the return, lower, connection on the boiler.. You have got it, well done!