Wood stoves with back boilers

tabbymctat

Hi, We are just considering installing a 23kw wood burning stove with a back boiler connected to our hot water and central heating. This will be linked up with an LPG tank and boiler (no mains gas). There will also be a thermal store to make the system more efficient. Does anyone have experience of these and how much wood they actually get through? We live in a normal 3 bed semi.


Thanks

mnbvcxz

If you are really going to try something that ambitious then be sure to google the "domestic renewable heat incentive" and check if it might apply to you. I think Broseley eVolution 26 is the only wood burner that is eligible. Of course having everything certified to qualify may end up costing too much of a premium to be worth it and it may never turn up anyway.... But it would be a shame not to check.

We were looking at something similar on a much smaller scale the other other day and the stove man muttered darkly about boiler stoves being hard to get up to an efficient temperature, smoking and tarring because of the water and being a pain. He is suggesting we just go with a basic simple wood stove and heat space directly with that. But we were looking at the simpler end of the market

When I have tried to add up the cost of wood, which is not easy as the moisture, type of tree and efficiency of the stove all vary hugely, I reckon it is somewhere between the cost of town gas at 5p a kw and lpg at around 8p a kw. Plus harder work stoking it but more fun to use of course. Be sure to look around for wood suppliers first of course.

Best of luck

Cardew

Integrating the wood burner with a CH system is more complicated than many people envisage.


I had such a system with an open fired Baxi and gas CH and finally had it disconnected - it was more trouble than it was worth.


The problem is that you cannot shut off the water to the log burner - well you can, but then you have a potential bomb on your property. No plumber would ever fit shut off valves because if ever the fire was lit with it closed, the water in jacket boils and bang!


You can have a Dunsley neutralizer or similar plumbed in - but it is quite a complex(and costly) procedure.


There are some threads on this if you do a search.

highrisklowreturn

Yes there is information here. I wouldn't listen to the advice the stove man gave you as it sounds utter rubbish. The water for a start is nowhere near the fire. Water doesn't cause smoke or tar. And what on earth is meant by efficient temperature? Codswallop.


It takes around 40 mins for my fire to heat the room, 80-120 for the radiators to be fully warmed and a tank of bath water ready and the house to be toasting. This of course is with a superior coal product such as petcoke.

highrisklowreturn

Cardew wrote: »

Integrating the wood burner with a CH system is more complicated than many people envisage.


I had such a system with an open fired Baxi and gas CH and finally had it disconnected - it was more trouble than it was worth.


The problem is that you cannot shut off the water to the log burner - well you can, but then you have a potential bomb on your property. No plumber would ever fit shut off valves because if ever the fire was lit with it closed, the water in jacket boils and bang!


You can have a Dunsley neutralizer or similar plumbed in - but it is quite a complex(and costly) procedure.


There are some threads on this if you do a search.

It's complex if you have gas. If you have oil with a non-condensing boiler its a breeze, and shouldn't cost more than £350 to link to central heating, including with a separate pump. Took 2 hours on mine to set up.


The kw reading sounds too high for your house - around 12-15 should be sufficient.

Greenfires

highrisklowreturn wrote: »

I wouldn't listen to the advice the stove man gave you as it sounds utter rubbish. The water for a start is nowhere near the fire. Water doesn't cause smoke or tar.


This of course is with a superior coal product such as petcoke.

Boiler stoves are almost always much more tarry than a dry stove when running on wood fuel, so it turns out the advice wasn't "utter rubbish" after all. If the system isn't set up correctly with regard to the return temperatures into the stove, the tar can become a real issue as the boiler never gets hot enough (due to a constant return flow of cool water) A lot of installers can't be bothered, or simply don't know all the ins and outs of setting up a wet system properly - there is a lot more to it than a standard stove.

The water is in the boiler which is inside the stove, and no-one with any sense at all would think the stove man was suggesting that water produces tar. It's the temperature of the water in the boiler that causes smoke from the wood to condense into tar - which in spite of your post, I'm sure you're well aware of. But as usual you need to try and stir things up a bit and get a reaction.

Same goes for petcoke of course - you know full well that most stove manufacturers will say that using it will invalidate your warranty - but you have to keep suggesting it anyway.

tabbymctat

Thanks for those replies. To clarify further - it was suggested that we have a thermal heat store in place of a normal water tank, which will store the heat from the fire when in use.


I also thought that 23kw was a lot, but he suggested 8kw to the room and 15kw to the water and radiators. We only live in a small 3 bed semi.


We have a free supply of wood (although will still require splitting).


It will have to be with LPG system as we don't have space for an oil fired boiler.


Hmm, food for thought. thanks. If anyone has any further suggestions or examples of successful similar projects, they would be gratefully received.

tabbymctat

with a heat store the heat goes to that and you turn off the individual radiators - does that get around the problem of not being able to turn the water off to the stove?

Greenfires

How much free wood have you access to? many people underestimate the amount they'll get through. They see these toy log stores on ebay and think they'll be sorted, and indeed they are....for about a week.

matelodave

We've just got a dry woodstove and manage to get through 4-6 reasonable sized logs in an evening, lighting it at about 6pm.It's not used to really heat the place - we've got a heatpump that does that.
The stove is more of a focal point with the benefit of reducing the electricity requirements of the heatpump (although not by much) and as a back-up in the case of power outages


I'd guess that if you were going to heat a house and your hot water it would be a bit like stoking the boilers in the Titanic - you'd need a hell of a lot of wood to keep it going and it would keep you fairly busy all day.

wrightk

the stove seems a little on the large size for your requirements. for example we live in a 3 bed semi and ours is 10kw to water and around 3kw to room. Even when it is absolutely freezing outside we can happily sit in shorts and t shirt indoors. and we're lucky its in the kitchen, if it was in the lounge it would be uncomfortable. plus stoves work at their most efficient when driven hard, and your choosing an expensive fuel if you dont have an unlimited supply of cheap/good quality wood