Will my gravity fed boiler have to be pumped?

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Hi, this is my 1st post, so be gentle with me.

I'm looking to add a back boiler to my wood burning stove and pipe it through a 2nd coil in my cylinder. Now the only way I can run the pipes is straight up into the loft, along the roofspace and back down to the cylinder. Would the gravity circulation still work, or would I have to pump?

Would this be okay, or would it need pumping?
Should the F&E be on the pipe run directly above the boiler, or above the cylinder?

Ta

Snoz
 
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The gravity would work provided you could return from the cylinder conection and fall back to the boiler, and not go via the loft.

if you fitted a pump it would have to be installed so as the vent was open to atmosphere, ( same as a normal install ).

The big problem would be interlocking the pump to the boiler, as circulation has to be guaranteed.
 
There must be an open vent with the 22 mm pipework rising directly upwards from the stove to the vent.

The pump will therefore have to be after the vent on the flow or the return from the heating coil on the cylinder.

If the pump should lose power or fail then the stove will boil the water out of the vent and cause problematic condensation in the loft.

It will therefore not be such a good idea if either you are prone to power cuts or the system is not very clean and the pump is likely to fail.

Another disadvantage is that once the cylinder water has reached the set temperature the system water will potentially boil to remove excess heat. A "heat sink" radiator is normally fitted to dissipate excess heat after the cylinder is satisfied but to give the cylinder priority a thermal control would be required on that radiator.

If you have free timber to burn thats all fine. Otherwise the economics and labour stoking requirement of burning wood to heat water when you already have gas or electricity becomes rather marginal.

Tony
 
doitall said:
The gravity would work provided you could return from the cylinder conection and fall back to the boiler, and not go via the loft.

Thats the problem, both flow & return have to go up via the loft due to the nature of the property.

Methinks it will have to be pumped.

Would a y-plan valve and pump triggered by a temp stat on the back boiler flow work.

My thoughts, pipe stat reaches temp, triggers pump and y-plan valve to pump water around the cylinder loop. If the temp drops or the power fails, the y-plan diverts the flow from the back bolier to a F & E tank plus heat leak rad, so if the fire does boil the water up it can escape and be replaced from the F & E.

Would I need an F & E on the pumped leg, or if I placed the F & E on the return leg would that cover both circuits?

Snoz
 
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Personally I think you should forget the idea if you cannot install the gravity circuit
 
Not heard of high level return ? ;) Saw it in a book years ago ........there is a relationship of one sixth height between height of Flow from boiler to amount of drop to cylinder..as far as I remember :confused: someone else must have seen the diagram.......all academic anyways in the context of this job
 
Oh yes, something else many forget!

As there is no control of heat in your wood boiler the F&E tank must NOT be plastic !!!!

It can be made to work but its very questionable if its worth it unless you have free wood as I suggested above.

Tony
 
Agile said:
Oh yes, something else many forget!

As there is no control of heat in your wood boiler the F&E tank must NOT be plastic !!!!

It can be made to work but its very questionable if its worth it unless you have free wood as I suggested above.

Tony

You can get high temperature plastic tanks which are suitable, but it needs to be 30/40 gallon in size
 
Agile said:
Oh yes, something else many forget!

As there is no control of heat in your wood boiler the F&E tank must NOT be plastic !!!!

It can be made to work but its very questionable if its worth it unless you have free wood as I suggested above.

Tony

All the free world I want, I get about 6-8 sacks a week of the stuff, so it piles high in the winter and we really rip into it Nov-Feb
 
If you have an unlimited supply of wood then why dont you get a professional wood burning boiler with the proper controls. I think they can modulate from about 20% to 100%. Then you can have a proper pumped system.

Even better if you can turn it into chips and use it yourself and sell the rest.

There are some people who want to use wood specifically because it is a sustainable energy source.

If I drove round London then I could pick up a lot of old palletts but would use petrol to get them, spend time collecting and cutting them up. Easier to pay the gas bill!

I dont know about the economics but I have seen farmers who use straw burning boilers. Quite large boxes though.


Tony
 

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