# Log burner on Gravity

[As soon as the stove heats and any water rises from the stove, it has to be replaced with cooled water descending to the stove. So you need the heat dump/cylinder above the stove.

The heat dump is all those parts of the circuit not providing the heat.
Water will ascend from the stove. It starts cooling straight away, and gets to the top having been pushed by more water from below. This is not magic, the stove is supplying the power. Meanwhile water will be drawn up from below the stove (or it is being pushed by the water ascending from the stove and thus bearing on the water in the rest of the circuit).

It is a cycle, that's the way it works, the water goes around and around.

Can't argue with that.

Your theory has the water ascending from the stove, replaced with water ascending from the cylinder below. Do you wind up with all the water in the attic? The water in the stove will boil.

Ah! but the water at the top of the circuit continues round the circuit, descending to the cylinder below.

Water in solid fuel systems often boils, even where the stove is below the cylinder.

It won't work. The end.

It is a cycle, that's the way it works, the water goes around and around. Hmmm......haven't I seen that somewhere before?

its all b!!!!!!!cks, pump it and stop p!!!!!ing about.....

Pumped? You mean gravity circulation won't work?
No, pumped through the uv coil (cant gravitate through a uv cylinder)

If the heat-link is a neutraliser, then that's the heat dump, with secondary pumped circulation to dissipate the heat.
As im sure your aware with solid fuel you cannot rely on pumps alone in case of power cuts etc.

Try thinking outside the box? What box? Could I suggest you try thinking within the laws of physics? It's not hard; hot fluid expands, rises to the top above cooler more dense fluid. It's how convection works.
[/quote]
Yes 100% correct. the cooler fluid is coming up from the return (after going through the cylinder).
Perhaps you need to read the posts again.
Cylinder ground floor(lowest point)
stove first floor (middle point)
F&E tank top floor(highest point)
So to re cap.
Flow off stove, up to top floor, tee to vent over F&E tank (cold feed can join in several places), drop down to cylinder flow, out return, down to below floor, rise all the way back to stove return. Its a loop, a circuit with heat rising and falling.

So to re cap.
Flow off stove, up to top floor, tee to vent over F&E tank (cold feed can join in several places), drop down to cylinder flow, out return, down to below floor, rise all the way back to stove return. Its a loop, a circuit with heat rising and falling.

The return water from the cylinder being the coolest and denser Will Not
Rise back up to the boiler where there is warmer water above it therefore
it wont circulate on gravity.

The return water from the cylinder being the coolest and denser Will Not Rise back up to the boiler where there is warmer water above it therefore it wont circulate on gravity.

This is a CIRCUIT. You cannot think of any one part in isolation.

Oilman,
ok.then if you drew a line level with the return of the boiler,
both the pipes below that line would be the coolest part of the circuit
would you agree to that ?.

the water above that line would be warmer and lighter therefore the same
return would not rise back up to the boiler being cooler and heavier

the flow from the boiler will only heat up to its highest point on the top floor and no more, it will not circulate.....

I have, unfortunately your not looking over my shoulder

Take a look at Dunsley web site, they have a scenario for an unvented cylinder connected to a heatlink (pumped of course).
You will see a flow pipe rising and descending with an aav on top, then dropping to a gravity circuit to act as a heat leak radiator circuit.

That would be this one.

http://www.dunsleyheat.co.uk/neutralizer89a.htm

The diagram shows almost the exact opposite of what you have claimed.

The gravity circulation is from the solid fuel stove (heat source at low level) to the neutraliser (heat dump at high level). The heat is dissipated from the neutraliser to the unvented cylinder at a lower level by a pumped circuit serving the UV cylinder and the CH.

Note also the note at top right, which mentions the requirement for a 'heat soak'. This is not shown and an UV cylinder cannot provide it.

To summarize, the scheme proposed by the OP will not work.

I suspect that you know you've made a mistake but will not admit it, even though your insistent support of an unworkable system may cost the OP a pile of money.

I'd suggest the OP should install a cylinder/heat soak in his loft ( or above the level of the stove on the first floor) with the F&E tank above this. This could then act as buffer vessel/neutralizer with pumped circulation to heat the ground floor cylinder when the upper one is hot.

I was pointing out the fact that a gravity circuit will work without the heat emmiters being above the heat source.
In the dunsley sketch why do you think they have ran a 28mm loop high and then down with just a aav at the top?
I was not using it as an example of how the op could pipe his cylinder as its blindingly obvious the sketch shows the cylinder pumped but the rads will gravitate hence 28mm pipework.
I cant understand why you think the circuit would stop to gravitate then boil.
Do you at least agree a cylinder would gravitate on the same floor as a stove with the pipework rising to floor above then droping to cylinder dropping further then rising back to stove, in a circle?

I was pointing out the fact that a gravity circuit will work without the heat emmiters being above the heat source.

No you were not; the OP proposed a cylinder below the stove.
It won't work.

In the dunsley sketch why do you think they have ran a 28mm loop high and then down with just a aav at the top?
I was not using it as an example of how the op could pipe his cylinder as its blindingly obvious the sketch shows the cylinder pumped but the rads will gravitate hence 28mm pipework. I cant understand why you think the circuit would stop to gravitate then boil.

The AAV is on the pumped circuit.

Only the heat dump rad will emit a significant amount of heat by gravity circulation, driven by the different water densities in the F&R pipes. There will be no significant gravity circulation through the CH rads if they're all on the same level.

The cylinder will not get any circulation by gravity. The stove will boil because there is no circuit to dissipate the heat.

Do you at least agree a cylinder would gravitate on the same floor as a stove with the pipework rising to floor above then droping to cylinder dropping further then rising back to stove, in a circle?

No.
You need the cylinder (heat dump) above the stove (heat source). Flow pipe hot, water ascends; return pipe cool, water descends. Got that?

Given nominal temperatures and pipe sizes and lengths, I could calculate the flow rates and work out whether it could dissipate the heat produced by the stove. But that's work.

Onetap wrote

The AAV is on the pumped circuit.

Its not when the overheat by-pass opens! Then its gravity circulation up to the AAV and down too the rads.

Onetap wrote

The AAV is on the pumped circuit.

Its not when the overheat by-pass opens! Then its gravity circulation up to the AAV and down too the rads.

Can you explain what that pipe that "must rise to high level to generate gravity flow" does? Hot flow goes up, hot flow stays up.

It must work, it's on the Dunsley website.

Can you explain what that pipe that "must rise to high level to generate gravity flow" does? Hot flow goes up, hot flow stays up.

It must work, it's on the Dunsley website.
[/quote]

You demonstrate a lack of understanding of gravity circulation.

You demonstrate a lack of understanding of gravity circulation.

Quite the opposite. My understanding of the flow of fluids in pipes is fairly comprehensive.

Gravity circulation relies on the difference in densities between the flow and return pipes to generate the pressure difference which drives the circulation.

There is no significant heat loss in this pipe, the difference in the ascending & descending temperatures is insignificant and so the pipe makes no contribution to the pressure differential or the gravity circulation.

If you know better, I invite you to explain it.

In fact, getting back on topic, the whole point of this discussion was your claim that you couldget gravity circulation between a first floor stove and a ground floor cylinder. We're still awaiting your explanation of that one.

It won't work.

I'll add to the argument / confusion.

This is my awful attempt at art.

View media item 9556
There is a loop of pipe above the stove and cylinder (flow), and another loop below (return).

Given that the heat enters the water at the stove, and leaves it at the cylinder, ALL the water in the upper loop is hotter than ALL the water in the cooler loop.

The left hand vertical is 2/3 hot and 1/3 cool. The right hand vertical is 1/3rd hot and 2/3 cool. Therefore the net temperature on the left is more than the net temperature on the right. In this instance the convection would be clockwise in my diagram, contrary to the intended outcome. It won't work. All that will happen is the water in the upper loop will eventually boil.

The horizontals can be ignored as they do not contribute to the convection.

Here you are, this should explain it.

http://www.engineeringtoolbox.com/gravity-heating-systems-d_189.html

"A self circulation heating system operates by the force created by the density difference between the hot and cold fluid. The head available forcing circulation through a radiator in a gravity system is proportional to the elevation - he - of the radiator or heating element above the boiler, and the temperature difference between the flow and return pipes."

If he < or = 0, then it won't work.

Got that?

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