Can one use a solid fuel burner (e.g. wood burning stove) to

A subject popped up within another thread ( //www.diynot.com/forums/viewtopic.php?p=1089728#1089728 ) and I would like to see it have its own thread (otherwise the initial thread is getting hijacked).

The question is... can one use a solid fuel burner (e.g. wood burning stove) to heat an unvented cylinder? I am confused here... I phoned the Solid Fuel Advisory Service and they said YES (but you cannot connect it directly in any way). However, the prevailing mood on the web seems to be NO. There must be a definitive answer out there somewhere (rather than just rule interpretation).

The wood burner will have it's own vent of course so can vent off if necessary.

A second question is: Is it likely/possible that a coil can boil the water in a cylinder?

I understood the Building Regs meant we couldn't connect an unvented cylinder to an uncontrolled heat source.

Some months back we supplied/installed two solar collectors and connected them to the solar coil on a Santon Premier that had already been plumbed in on the boiler coil. I found out later that day the only heat source was a large wood burner boiler I spoke to the builder and then later the Plumber both stated that Building Control in West Sussex will approve the installation of unvented cylinders to uncontrolled heat sources. The cylinder should if fitted in the UK be G3 compliant and come with full G3 kit.

I have now spent the last months thinking about it and cant see a problem provided the cylinder is on a pumped circuit and the system can fail safe to a heat leak. With the two port supplied fitted it the flow and a single check valve in the return it would be perfectly safe to install, I guess that's the thinking of West Sussex Building Control too.

Yes a cylinder could be boiled via a coil.

The regs deffinately say not, one reason i see is that a solid fuel boiler has no high limit cut off which is one of the safety chain required.

As mentioned above though personally i dont see why it couldnt be possable to say use pipe stats and a 2 port(spring return) to ensure that should overheat occur the cylinder becomes disconnected and the heat could be lost in a large buffer/heat leak, would also include a TPRV on solid primaries.

the regs are old now, plastic d2 is becoming more common and soil connection but still isnt in the regs.

Thats my view on it some will agree others wont.

The regs are very clear, you cannot directly connect to an uncontrolled heat source.

I thought that for many years and told my customers the same but the system I referred to above was installed and past by the LBC in Ticehurst East Sussex not West Sussex as I'd said.

If the cylinder could be heated by gravity then it would be risky to say the least, what if it were on the same floor as the WB and had to be pumped, wheres the danger?. If you used a buffer cylinder you could connect that to unvented as it wouldn't be "Directly connected".

The learned Onetap posted a while back on how to do this using a low loss header to make the connection indirectly through thermostatic control which would be in keeping with what the Solid Fuel Association advise afaik.
Diyers regulary connect their UV's directly to solid fuel.
BOOOOOOOOOOooooooooooooooooooooooooooooooooooooom.

lcgs said:

The regs deffinately say not,

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Would you mind quoting what the regs say that leads you to make this statement please as I would find it very useful.

ajstoneservices said:

The regs are very clear, you cannot directly connect to an uncontrolled heat source.

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I agree... but a coil is an indirect method of heating water is it not so okay with the regs?

Let's move this a stage further. What if I connected my woodburner primary circuit to the primary circuit used by the unvented cylinder with just a heat exchanger (no water mixing from one circuit to another). So when wood burner circuit is up to temperature the pump kicks in on the unvented circuit and this steals heat from the heat exchanger. Is this directly connected or indirectly connected and therefore allowed or disallowed?

Norcon said:

Diyers regulary connect their UV's directly to solid fuel.
BOOOOOOOOOOooooooooooooooooooooooooooooooooooooom.

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UV's have safety features to prevent this though...

Goldspoon said:

ajstoneservices said:

The regs are very clear, you cannot directly connect to an uncontrolled heat source.

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I agree... but a coil is an indirect method of heating water is it not so okay with the regs?

Let's move this a stage further. What if I connected my woodburner primary circuit to the primary circuit used by the unvented cylinder with just a heat exchanger (no water mixing from one circuit to another). So when wood burner circuit is up to temperature the pump kicks in on the unvented circuit and this steals heat from the heat exchanger. Is this directly connected or indirectly connected and therefore allowed or disallowed?

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This is direct and disallowed!
Think low loss header ,neutralizer or separate thermal store to make the system indirect.

Goldspoon. dont have tem to hand but will dig it out.

Norcon,cant see why a low loss would help, its purpose is to stop circulation through multiple circuits whether they be pirimary or secondary. to me your control is still only acheived through the pump and stats on the secondary cct still with no high limit temp control of the solid fuel burner.
(Dunsley neutraliser instrutions have anti boil stat and dump to large heat leak- 1st floor rads, as its get out which is all a play on the words in the regs)

Please feel free to educate me on this one,cos we fit headers but not for this purpose.

Have this question asked often. Yes you can connect a solid fuel boiler to an unvented cylinder but it has to be via a pumped indirect circuit. This circuit has to be open vented and it also advised that at least 1 rad 10% of the solid fuel appliance output be a gravity heat sink.

This is exactly the same as many solar applications with the exception of the heat sink rad. They have pressure relief valve.

The greatest problem you will have is getting any manufacture to agree.


quote below from tribune.

Their advise to me was as i have said above.


"The boiler may be Gas, Electric, Oil etc but must be under effective thermostatic control. Uncontrolled heat sources such as some AGA’s,
back boilers, solid fuel stoves, etc are NOT SUITABLE. Please contact our technical department for guidance.
Connect the two port zone valve ( indirect only ) into the primary flow pipework. The direction of flow arrow should be towards the
primary flow connection.
On twin coil cylinders we have provided an extra thermostat boss should you wish to use it. Again a two port zone valve should be fitted (supplied)."

I've just flicked through CITB Unvented Hot Water Systems Reference Manual and didn't see any mention of solid fuel.It hasn't got an index, so it may be in there somewhere).

PS Edit. P6. "The energy supply to an unvented system must be 'controlled'. This will generally rule out the use of unvented systems that are fired by either soldid fuel or solar energy."
IMHO the use of a low loss header would control the supply of heat from any source, but if you want to install one of these you'll have to design it and be responsible if it doesn't work as intended.


The last time I looked at a Manufacturer's Installation Manual, it specifically recommended against solid fuel unless there were other, unspecified safety devices; i.e., you assume design responsibility and have liability insurance for the worst scenario.

The short answer to daft DIYers or knuckle-dragger, time-served plumbers is no, you can't.


The longer answer is that;

1) the unvented water heater must have the supplied 2-port spring-return zone valve fitted; the warranty is invalidated without it and the system is unsafe without it. The 2-port valve isolates the unvented cylinder from the heat source when the control thermostat is satisfied OR the power supply fails.

2) the solid fuel system must have an open vent and a heat dump radiator. The system must be capable of safely dissipating the heat from a charge of solid fuel; it would usually do this by emitting heat from the radiator and, in extremis, boiling off the water in the boiler. There must be NO isolating or control valves on the heat dump system and it must still work without power, by gravity circulation.

IMHO you could heat an unvented hot water cyclinder from a solid fuel boiler, but it must NOT form any part of the heat dump system because it will be isolated if the solid fuel system overheats or if the power fails.

lcgs said:

Norcon,cant see why a low loss would help, its purpose is to stop circulation through multiple circuits whether they be pirimary or secondary. to me your control is still only achieved through the pump and stats on the secondary cct still with no high limit temp control of the solid fuel burner.

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Quite right; the low loss header would prevent gravity flow to the unvented water heater. Flow would only occur when the cylinder thermostat was calling for heat, the 2-port valve was open and the pump was running. It is a safety device to prevent the cylinder overheating by gravity circulation.

It is not a part of the temperature controls for the solid fuel boiler nor the heat dump system.

Great stuff... thanks everybody. I am starting to get more of an idea of the picture now.

Onetap wrote

Quite right; the low loss header would prevent gravity flow to the unvented water heater

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But why would you want gravity flow from a solid fuel appliance to an unvented cylinder?
To make it go booooooooooooooooooom. lol
A thermal store or dunsley neutralizer is pretty much just an extension of a low loss header anyway.

Your posting is here about the use of a low loss header.........
//www.diynot.com/forums/viewtopic.php?t=110278

Norcon said:

But why would you want gravity flow from a solid fuel appliance to an unvented cylinder?
To make it go booooooooooooooooooom. lol

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You don't. The low loss header stops gravity circulation causing nuisance overheating of the unvented cylinder.