A Quick Woodburner/Central Htg Question

11 Jan 2011
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United Kingdom
Hiya Folks,

Notwithstanding all the issues regarding integrating a woodburner with back boiler into a vented system I have a simple question if anyone could help please.

I have a spare copper cylinder lying around so was toying with the idea of using the woodburner to heat the whole tank ie flow in at the top and return out the bottom (thermal store?), and running the oil boiler return pipework through the single coil to preheat it thereby making the boiler fire less - using less oil.


Will it actually pick up enough heat from the cylinder in the rather short journey through the tank?

Regards, Flash
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can't do any harm, but when you're woodburner isn't lit, it will alsotake heat out of the system so you really would have to think about a 2 or 3 port valve (depending on the pipework layout) operated by a pipestat near the log burner to stop it circulating through the tank circuit when the fire isn't lit, depends how much you light the fire really
Thanks sparkiedave, that was going to be the idea with this system. I have a cunning plan of thermostats/valves but it was more a case of finding out just how much heat could be exchanged this way. I am only looking at it because I have a spare cylinder.

If the answer turns out to be 'very little' I shall probably invest in a new 2 coil tank system or look at the possibility of getting my spare tank modified with another coil.

Does anybody have any ideas regarding my original question?
Your "thermal store " will probably start boiling and when it does what would you intend doing then ?
Frankly its a bad idea. on the otherhand theres nothing stopping you having a gravity hot water system installed, heated by a woodburner.
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I also think its a very bad idea! It seems you are just trying to find a use for the cylinder!

My advice would be to fit a good size rad to the woodburner output on a gravity circuit and let that augment the other heating from the oil burner.

My friend has a large log fire and leaves all the doors open and that provides most of the heating when the fire is lit.

Why not plumb the spare cylinder in tandem with the main house cylinder so as to preheat the water entering the main cylinder? I did this with a 160l cylinder I got off Eblag and now I'm running my solar panel through the coil.
Thanks for all the replies folks. Whatever design I come up with, I appreciate I will always have to dissipate the energy from my 27000btu boiler. With a simple design of stats, thermostatic valves etc this really isn't the problem. It is no different to any other setup that has a solid fuel heater gravity feeding a circuit.

There are many ways to skin a cat and I notice from several heat bank/thermal store websites that one common way to do this is to indirectly heat water much the same way that most of us do via our normal DHW cylinder, only in reverse. You use the heat source to heat a large volume of water then cold water comes in, goes through some sort of heat exchanger and hot water comes out. I could just do the DHW but with only 2 of us showering once a day, and DHW only accounting for 20-30% of boiler use I don't think it is the best use of my free heat; I live in an old house with no cavity etc, and the woodburner is running all day, every day at the moment.

One of the simplest ways is to heat the oil-fired boiler water and let the existing CH/DHW circuit decide what to do with the water. It involves least disruption and least complexity. I would like to do this without vast expense using things I already have hence my plan to use the cylinder I have spare.

I appreciate that I will get a temperature rise with this system but without actually having the woodburner and testing it, I am not sure by how much. If someone is able to say 'I tried this and it didn't really make much difference' then I can reconsider, probably buying a cylinder with a better arrangement of coils but I would like to avoid this if possible.


ETA Thanks ade2k, that was one of the other plans a little further down the line if this system didn't work.

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