Woodburner water heating system(unconventional )

[mysteryman]

Someone suggested a dry woodburner.

What you are proposing is a very complex system. It may not be worth doing unless there is to be serious use of the woodburner. Furthermore, all the extra complication involved in making the system safe but controllable can reduce the efficiency of the main boiler, so that the savings from the woodburner can be nullified.

 

[rayburner]

I was hoping not to have to use the oil burner very much at all and with the proven unreliabilty of my Rayburn it'd be nice to be able to heat the whole house and get some hot water if it packs in suddenly.
A fully integrated system would be complex as I looked into all but this way with 2 virtually separate systems I can't forsee many problems although I never did it before so I can't only throw ideas around on here to get some insight
As I have most of the components and the pipes are in already it's only going to cost around £500 to find out which doesn't get you much oil these days.
I know a couple of people who only have solid fuel burners (mainly coal) with CH and HW and they don't have any problems

 

[Onetap]

You mean actually inside the fire box where the wood goes? On mine which is an old Hunter most of the housing is the boiler back and sides and it's completely covered with fire bricks no signs of corrosion at all

That's back-end corrosion, caused by low return temperatures. You'd couldn't run UFH alone directly off the heating system for that reason. You'd need a thermal store/buffer vessel and a mixing valve so that the UFH system was mixing cool return water with the very hot water from the store. Back end corrosion could rust through a boiler in a few months.

Electrolytic corrosion, in the water side, is usually prevented by adjsuting the pH of the water to 8 or 9. Most domestic inhibitors use sodium molybdate which works by deposting a inert coating on exposed metal.

 

[Flashheart]

Hi Rayburner, thanks for the message. I notice all of this is 5 months old so I was wondering what you ended up doing. Did you use your woodburner directly as in a thermal store or did you do it indirectly and connect the woodburner to the coil?

I am interested as I am considering a similar system and wanted to know if using the thermal store idea, would the coil of a standard DHW tank transmit sufficient heat (I have a spare single-coil cylinder) or would I be better off buying a new cylinder with longer coils in?

Does anybody else have any experience of this?

 

[Nige F]

Galvanised Tank connected to Copper Pipe? Sounds like electrolysis...

Could electrolytic corrosion not be a concern with that arrangement?

What an interesting project.

Just buy a big lump anode - maybe from a boat yard as they say oop North - Foorkanall booat

 

[Nige F]

double post

 

[rayburner]

I've been slowly rebuilding my heating system for a few months with trv's and rerouting pipes etc. I found that my existing CH pump wasn't upto the job of pumping around all the extra underfloor heating sections so fitted an extra one with a mixing valve.
My next job is to fit the tank for the woodburner and plumb in the extended 22mm F/R. Fortunately with the addition of the UFH pump I now only have to fit a motorised valve to the WB "heat out" circuit.
Tank stat senses the heat from the WB >opens the MZV> UFH pipe stat senses the heat and turns on the pump>ufh pump circulates water around the whole central heating system without need to open the main CH MZV.
So long as I get good convection from the WB I can't fore see any major problems

 

[rayburner]

Hi Rayburner, thanks for the message. I notice all of this is 5 months old so I was wondering what you ended up doing. Did you use your woodburner directly as in a thermal store or did you do it indirectly and connect the woodburner to the coil?

I am interested as I am considering a similar system and wanted to know if using the thermal store idea, would the coil of a standard DHW tank transmit sufficient heat (I have a spare single-coil cylinder) or would I be better off buying a new cylinder with longer coils in?

Does anybody else have any experience of this?

Hello
I'll be using the water stored in the tank to circulate into the WB.
I will use the coil in the tank to get heat out. This way I can have
the cylinder vented and have rust inhibitor in there along with it's own
metal loft tank. Whether the tank will be big enough or the coil will be of sufficient size to extract the heat fast enough -I don't know

 

[Norcon]

Whether the tank will be big enough or the coil will be of sufficient size to extract the heat fast enough -I don't know

If its a standard boiler input coil then it will most likely fail in reverse as an output coil.
Check with the manufacturers. They might know.

Found out the hard way recently involving coils after the manufacturer assured me it would work.
It's hard to beat a good decent plate heat exchanger.

 

[rayburner]

I'll give Albion a call see if they have a better idea of things. I'm guessing that one of these tanks that have indirect hot water/mains pressure would work better as they have a larger coil inside for rapid heat transfer ??
Trying to avoid any sort of bespoke/special tank as the cost seems to go up
massively for dual coil etc.
Also the coil would be better positioned at the top rather than at the bottom like a normal cyl

 

[Onetap]

It's hard to beat a good decent plate heat exchanger.

The two tube-in-shell heat exchangers in my shed beat it, or they will do, one day.

I once made an enquiry about replacing a PHX with a tube-in-shell job, since the PHX had blocked with sludge from the heating system it was connected to. I was told they could make it, but it would be 40' long and the spot price of copper would go up when they bought the tube.

Woodburners usually have a lot of crud in them, if the water boils or gets hot enough to evaporate a proportion of it.

 

[Norcon]

The two tube-in-shell heat exchangers in my shed beat it

What is their output and cost?
And then I can make a comparison.

 

[Flashheart]

It will be interesting to see if sufficient heat can be extracted from a standard tank only in reverse.

One of my many cunning plans was possibly buying a 2 coil tank, using the bottom coil with the woodburner (indirectly) heating the tank as per normal, running the CH return through the upper coil (to preheat & save boiler firing) and then use the main body of water in the cylinder to refill my existing DHW cylinder as it is drained off.

 

[Onetap]

The two tube-in-shell heat exchangers in my shed beat it

What is their output and cost?
And then I can make a comparison.

Output; er, dunno.

Cost; £0.

 

[Norcon]

Nothing costs zero.
You must be able to post some figures as to the capability of your heat exchangers.