Woodburner water heating system(unconventional )

2 Aug 2010
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United Kingdom
I'll be fitting a woodburner with back boiler v soon and have some ideas for the system I'd like the experts to comment on please. It's a little unconventional but I think it's quite simple and should work.
The house already has a oil fired rayburn which does the CH and HW which will be left as is for simplicity and I will fit another new larger capacity cylinder for the woodburner fed by 28mm pipes gravity/ convection I will then fit a pump and blending valve to feed a largeish UFH zone feeding from the 28's not in series.
The new cylinder will be a normal gravity fed vented sharing it's supply from the existing loft tank and it's water will circulate through the UFH pipes and the wood stove boiler.
The tank will also have a single exchanger coil that can be used either to extract heat into the existing radiators or put heat in from the oil boiler.

Will it work or is it a waste of time and effort ?
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Any chance you could post up a sketch mate? My eyes started to glaze over after the first few words!!
Wouldn't know how to post a sketch :confused:
I'll condense it
Woodburner>Heat store tank
UFH feeds from the pipes (using the same water not a coil in the tank) maybe creating better flow through the WB?
Pipe stat on the flow triggers the pump at say 35degrees for the UFH
Excess heat stored in the tank
System is unpressurised so fairly safe
Only problem I can see is if the WB puts out more heat than the tank and UFH can store in which case I could use a coil inside the tank triggering somehow the existing CH pump and motorised valve but without firing the boiler
Is it a 'thermal store or heatbank tank'?
Have you got addiational connections on the tank for the WB sove?

You could always do a 'fag packet sketch', scan it & upload it onto photobucket.
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I don't have a scanner or software sorry.

The tank would just be a large capacity 250 litre tank with one coil which I guess is acting as a heat store- cold feed from the WB at the bottom and hot feed at the top. UFH circuit would just tap off from these pipes. Single coil in the tank would be used to plumb in the existing pressurised CH.
I haven't bought a cylinder yet
You seem to be using it as a direct system.

Standard CH pumps are meant to be used in closed and inhibited systems.

However, I have been using one for over 10 years and its no problem. Just not what its designed for.

The feed tanks should not be made of plastic.

As long as its all open vented then you should not blow yourself up! But even so a professional to see the design would be far safer.

Unfortunately the loft tank is plastic bought new this year 70 gall I think also the pipes for vent and feed are JG speedfit PEX but the last 3 metres to the tank will be copper will this be a problem?
Only way I could pressurise the UFH side is by using either another coil in the tank but I'd be happy to get 10years from a pump and they are fairly cheap.
But 'Primary' water should be used for both boilers!! You can always use a SS plate heat exchanger for the UFH. But to be frank, this needs a lot of design & not for any DaftyDIY'er!!
I don't know what the Regulations in Scotland are, but in much of the UK Solid fuel (wood) Heating systems also have to comply with Building Regs and be installed by a competent (HETAS) Registered firm. ;)
I had a heating engineer in to move the existing cylinder 3 feet to the right.
First he connected the flow and return the wrong way then he forgot to plumb in the kitchen radiator which was also the heat dump for the rayburn so it had to be hastily attached to the normal circuit. During the evening he hadn't tightened a fitting properly and the whole system emptied into the kitchen below. The pipes from the loft tank were fitted too low and had to be raised to allow the ceiling to be put in due the pipe bends. Now I have to figure how the heat dump circuit was connected to stop the pump over run and boiler overheat.
Then he wanted to sell me a air source heat pump :eek:
I explained that I'd be dead before it paid for itself :rolleyes:
I'm sure most engineers aren't like this
So I'm sure you understand why I am leaning towards DIY system
I don't know what the Regulations in Scotland are, but in much of the UK Solid fuel (wood) Heating systems also have to comply with Building Regs and be installed by a competent (HETAS) Registered firm. ;)

With the greatest of respect Scotland is part of the UK and in these parts LABC will permit anyone to fit Solid Fuel.

To be frank there was a 'poster' on here the other day that was fully HETAS trained & that deadbeat didn't even know how a gravity system worked..............So HEATAS is like OFTEC, f4cking useless!!
Ordinary domestic woodburners do not perform well when heating water. The efficiency drops off significantly. There is the risk of severe corrosion in the combustion chamber if the circulation isn't controlled. Read through everything here for some useful info, then think about running it dry instead.
Anything solid fuel that has water in it will normally require pumping, consider what may/will happen should there be a power cut (any part of the UK gets them) and there is an uncontrolled burn going on. Plastic tanks and PEX notwithstanding, where would all that heat energy go........

Get an expert in. They do exist.

I agree with oilman, WB stove installation need careful installation/design. Woodwarm are good and there's a wealth of knowlege on their web site.

Perhaps you need a neutral point in your system for the two boiler??

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