Designing Back-boiler fed central heating system

[Chevetter]

no.

 

Looks good

 

why the valves? having them shut by mistake could be interesting.

 

is it also possible that the overflow, once it gets some water through it will start syphoning?

 

not clear from the diagram, the return from the radiator should run downhill if possible

 

Hmmm, not a bad point about the siphoning. The valves are there because I may want to restrict the overflow as per a few posts back, but agreed, the whole thing could explode if I shut the top one by mistake.....

 

The return will struggle to run downhill to be honest - the stove is well off the floor as I sain, plus the slope of the boat as well.... but I'll make it go down as far as I can.

 

By the way, does anyone have any ideas as to what I can use for a header tank?

Edited September 21, 2009 by Chevetter

[Chris Pink]

By the way, does anyone have any ideas as to what I can use for a header tank?

 

if you need it pressurised then an expansion tank?

 

http://www.vehicle-wiring-products.eu/VWP-...ries/radfan.php (bottom of the page)

 

or get one from a scrappy

 

if you need an open one then any open top tank will do.

[Chevetter]

if you need it pressurised then an expansion tank?

 

http://www.vehicle-wiring-products.eu/VWP-...ries/radfan.php (bottom of the page)

 

or get one from a scrappy

 

if you need an open one then any open top tank will do.

 

I think I want it sealed, so no steam etc. can get into the boat, but it won't actually be pressurised.

 

A check valve (or non-return valve) on top of the overflow pipe should solve the siphon problem.

 

[RLWP]

I think I want it sealed, so no steam etc. can get into the boat, but it won't actually be pressurised.

 

A check valve (or non-return valve) on top of the overflow pipe should solve the siphon problem.

 

 

If it is sealed and you heat it up - it is pressurised!

 

Richard

[Chevetter]

If it is sealed and you heat it up - it is pressurised!

 

Richard

 

I know I might sound thick but I'm not that thick - note the vent pipe!

[John Orentas]

"Designing Back-boiler fed central heating system".

 

For many years I played about with this idea but kept coming to the conclusion that the advantages of having a few radiators added to a solid fuel stove could be only very marginal and I kept returning to the fact that no extra heat is ever produced by the stove, the best you may accomplish is an improvement to heat distribution.

 

On my first 40 foot boat, a cruiser stern, I situated the stove at the very front of the cabin, as a result the rear picked up very little heating and to make things worse every time the front doors were opened a lot of hot air went out and a lot of cold, smoke filled air came in.. On my second effort with a 50 ft traditional type cabin I placed the wood burner in the centre of the cabin resulting in very even heating of the entire space.

 

Being slightly inspired by those very expensive 'Eco-thingy' thermo powered fans, I experimented using my friends boat with a computer fan blowing across the top surface of the stove, this worked surprisingly well giving a very noticeable increase in temperature in the rear part of the boat.

 

The moral, if there is one to all this, is to give a lot of thought to the location of your stove and perhaps look for ways of moving warm air around the boat, but as always 'keep it simple'.

Edited September 21, 2009 by John Orentas

[ChrisPy]

By the way, does anyone have any ideas as to what I can use for a header tank?

a small cistern - black plastic from screwfix including float valve

 

Does it have to be literally directly above? That will create a heck of a lot of work for me!

 

A better idea from my point of view would be to take-off directly above the stove but actually vent the steam somewhere else.

that'll do, as long as the run is short.

 

Should the boiler boil up or produce steam in this design it gets dumped into the bilge.

assuming you mean the bilge below the cabin, why dump water into a perfectly dry bilge?

[Chevetter]

assuming you mean the bilge below the cabin, why dump water into a perfectly dry bilge?

 

I don't have a bilge below the cabin - its very small and (unsurprisingly) is situated underneath the prop at the back of the boat. The entire deck drains into it.

[smileypete]

I think I want it sealed, so no steam etc. can get into the boat, but it won't actually be pressurised.

 

A check valve (or non-return valve) on top of the overflow pipe should solve the siphon problem.

 

 

There must be NO valve between backboiler and vent!!!

 

BTW I think normal practice is to direct the vent into the expansion tank so any water ejected along with the steam won't be lost. If too much water is lost the thermosyphon will stop and the system can only then boil dry.

 

I would give the expansion tank a closely fitting lid (but not sealed/fixed in any way) and have a pipe to direct steam outside.

 

cheers,

Pete.

Edited September 21, 2009 by smileypete

[Chris Pink]

...but not sealed/fixed in any way

 

aha, one from the school of unpressurised only then, Mr Pete?

 

...and your thoughts on a pressurised system with a car cooling system expansion tank with rated cap?

[smileypete]

aha, one from the school of unpressurised only then, Mr Pete?

A tight fitting expansion tank lid that doesn't seal just covers the possibility of a steam vent/overflow pipe from the expansion tank to outside getting blocked somehow.

 

...and your thoughts on a pressurised system with a car cooling system expansion tank with rated cap?

For a boat, I can't really see the advantages. I'd expect most if not all boat stove backboilers are intended for vented systems, so might be a bit of a grey area.

 

For a house, a sealed central heating system does have clear advantages, (there's plenty of info on the web explaining why.)

 

cheers,

Pete.

[Smelly]

There must be NO valve between backboiler and vent!!!

 

cheers,

Pete.

 

Now there's some sense in that, but a big "DANGER" sign might be adequate...

 

OTH... Having thought about this, the way our system evolved was an overflow pipe from the bottom of the system, with a bleed/vent pipe with a gate valve from the top. That way it self bleeds but even with the gate valve turned right down any expansion has somewhere to go...

[Chris Pink]

For a boat, I can't really see the advantages. I'd expect most if not all boat stove backboilers are intended for vented systems, so might be a bit of a grey area.

 

For a house, a sealed central heating system does have clear advantages, (there's plenty of info on the web explaining why.)

 

I've never really got a handle on this, i know how a gravity system works (roughly) - heat water behind stove, rises and pushes all the rest around above it and sucks cold in below it.

 

am i right so far?

 

so what difference does water pressure make to this system? is it simply that in a sealed system (that doesn't reach blow-off pressure) no topping up is needed and in an open system there will be losses?

 

or is there an increase in the push and suck mechanism as well at higher pressure?

[smileypete]

Now there's some sense in that, but a big "DANGER" sign might be adequate...

 

OTH... Having thought about this, the way our system evolved was an overflow pipe from the bottom of the system, with a bleed/vent pipe with a gate valve from the top. That way it self bleeds but even with the gate valve turned right down any expansion has somewhere to go...

 

I'd remove the gate valve!

 

It's just waiting for someone else to come along later and 'complete the jigsaw'

 

cheers,

Pete.

Edited September 22, 2009 by smileypete

[Smelly]

I'd remove the gate valve!

 

It's just waiting for someone else to come along later and 'complete the jigsaw'

 

S'funny you should mention... evolution

 

cheers,

Pete.

 

I forgot to mention that the bottom of the system is also vented to the expansion tank so I've no worries and I'd think about doing that on such systems more often, no go bang and you can reduce the amount that can get vented with no guilt.

 

Running a common rail across the return pipes would make that feasible on OP's plan...

Edited September 22, 2009 by Smelly