Following on from yesterdays thread about using wood being a cheaper greener fuel, I would like to investigate installing a wood burning appliance (stove, fire, boiler) probably a fire with a back boiler. If possible I would then like to link this system to my existing gas central heating system, so the solid fuel system contributes some energy to hot water and radiators to maximise the efficiency, does anyone have any experience of linking solid fuel and gas boilers ?
It's only going to be efficient if the solid fuel bit is fairly efficient, so use a stove or a pellet boiler - open fires are mega inefficient. I'd link the solid fuel device and the boiler through a thermal store like
I *had* a multifuel Franco-Belge oven sat next to my old boiler, the two were just piped in series into the heating system.
The FB literally gobbled up either wood or boiler nuts, the hob would get nice and warm, but you couldn't cook with the oven, it never got above luke warm. More irritating, however, everything in the kitchen got covered in a fine layer of black dust and soot over a period of a few days. I had a new flue installed, that made no difference. Oh, and if you get a power cut and the stove is going full chat with no standby generation, the water boils, like very quickly!
It's now long gone, together with the old boiler, and I'm constantly marvelling at the efficiency of the new boiler. OK so it's been a mild winter, but an extra three months before an oil refill, compared to the old boiler.
For many years, we linked a Trianco oil-fired boiler and a Morso wood-burner. We used a Dunsley Baker Neutraliser, basically a steel box with various connections on it. It's in my garage at the moment, in fact, as last year we changed to a fully-pumped system and a wood-burner without a back-boiler.
The set-up seemed to work well, and has the virtue of simplicity, there being no moving parts, compared to the alternative of using motorised valves.
Yes it can be done with a heat bank/thermal store, or a Dunsley? neutraliser if you only want to heat hot water. Our Rayburn heats the water in winter, but uses a system that is not recommendable!
However, it is almost certainly not worth doing unless you have a supply of free wood and are burning lpg rather than mains gas. The appliance will cost from a few hundred pounds up to several thousand for a log burning boiler, plus a similar amount for the thermal store.
Wood burning appliances are messy. If the boiler is outside or you use an externally fed pellet system it's not a problem, but anything that is fed internally will create lots of dirt.
Likewise, anything affordable is going to need a fair amount of work in use. If you have your own wood supply it will need cutting, splitting and storing for a couple of years to dry. Anything but the more sophisticated boilers needs constantly refuelling during use. The ash needs to be removed periodically (often leaving a trail of fine dust as you take it out of the house!) and flues need to be swept, probably twice a year if the heater is used frequently.
You'll also need a fair amount of space to store the fuel.
If you are in an urban area you need to think about the clean air act. There are very few wood burning appliances that are capable of burning cleanly enough to comply. A few upmarket stoves and possibly some boilers may be OK. (Wood may be carbon neutral but it can, and usually does emit lots of other undesirable pollutants.)
Thanks for all your replies, it seems that nobody is very enthusiastic about wood burners or linking the with gas systems. However if I've got to have a wood or multifuel burner (wife says so) I determined that it should be as efficient as possible so that most of the heat does not go up the chimney.
There seems to be three alternatives for linking boilers mentioned so far 1) thermal store 2) Dunsley Baker Neutraliser 3) motorised valves.
Will have to a some searches and a good bit of reading I think, still not clear on the advantages and disadvantages of the above.
Wood burners are pretty nice things, but there is a fair amount of manual labour associated with them, plus they tend to generate a lot of ash and a fair amount of soot.
If you got for high temperature combustion, you eliminate the soot and the pollutants that wood produces BUT you pay a premium for thee technology.
Guess why we all abandoned coal systems in the 50's and 60's in favour of gas and oil..
Googled 'solid fuel boiler link' and found this site, they seemed very happy with their moterised valve system, a H2 Control Panel manufactured by Heating Innovations Ltd. This system links up two boilers a Baxi Bermuda G.F. Calor Gas (Liquid Propane Gas) Boiler and a Rayburn Supreme Solid Fuel and Wood-burning Cooker which includes a back boiler. They estimate, after a quite a short trial period that their Calor Gas bill has been reduced by 80%
Apart from the caveats over sourcing, preparing, storage and handling I'll give a plus to what you are talking about. I've got a similar set-up using a closed log burning stove in the sitting room which has a boiler in it. The CH is off an oil burning boiler (no gas here) and the two are coupled through a Dunsley Neutraliser. Gravity feed form the wood burner and a second pump from the oil burner. Only one valve to select CH or DHW. A differential pipe thermostat shuts off the oil burner when on the wood burner is hot. Works fine though I would admit to wondering about the economics of it - financial and physical, but on the basis that we wanted a log burner in the sitting room it might as well have a double use.
One simple set up which might be useful is to couple your back boiler to a dual coil hot water cylinder. This then gave us hot water from the wood burning stove in preference to using gas. There was also a thermostatic control which released surplus heat into the central heating system, though to be honest the room with the stove in would have been unbearably hot if we'd ever generated enough heat for the central heating this way.
Keeping up with the wood supply was a real challenge, but eventually the area became a smokeless zone and I had to install a gas fire.
Have been reading about the Dunsley Neutraliser on their website
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been struggling understanding the layout, am I right in thinking that the heat from the solid fuel boiler is gravity fed to the neutraliser and not pumped ? and that an extra pump is required to feed the radiators.
I don't understand why you want to connect the wood burner to your central heating. If you want efficiency, then dry burners are better, and are coupled to your central heating via the thermostat anyway. I'd save the money on connecting the two systems and buy a condensing gas boiler if you don't have one already, and more loft insulation. Install a small burner ~5kW so that you don't overheat the room, or require extra ventilation for combustion. Don't forget you will need a gravity hot water connection as well.
A thermal store is probably the best route to go with the abilty to dump heat into the heating system when (not if...) it gets too hot. How you connect your heat sources to the store is the tricky bit, probably best to use a Dunsley Neutraliser so that heat from the wood burner doesn't find it's way to the oil boiler and up the oil boilers flue.
What ever you do there should be no valves in the wood burners circuit, it needs to be a gravity loop and have some means of dumping heat when it needs to a wood burner on for a few hours is perfectly capable of boiling a cylinder of water. The lack of valves is partly safety and partly so you don't have to put your only source of heat out when there is a power failure...
Sorry Tom, I may have accidentally misled you, I think we are going to have a wood / multifuel fire installed in the lounge, wife wants one, done deal. My only input will be, given that we are probably going to have one I would like to ensure that it is as efficient as possible and that most of the heat does not go up the chimney. To this end I would like my wood fire to have a water jacket and contribute to the heating of the water and the radiators.
At the moment I'm looking at three possible alternatives for linking the system1) thermal store 2) Dunsley Baker Neutraliser 3) motorised valves (H2 control system).
Sorry Tom I may have accidentally misled you, I think we are going to have a wood / multifuel fire installed in the lounge, wife wants one, done deal. My only input will be, given that we are probably going to have one I would like to ensure that it is as efficient as possible and that most of the heat does not go up the chimney.
To this end I would like a fire with a boiler that will contribute to hot water and radiators.
There seems to be three alternatives for linking solid fuel and gas boilers 1) thermal store 2) Dunsley Baker Neutraliser 3) motorised valves (H2 control system)
You can link these with a dunsley baxter neutalizser, I always found these are a poor mans solution. Better is to use some sort of heat store with multiple coils, which has many other advantages, and lots of cost.
A solid fuel buring appliance, must have a method of moving the heated water in the event of a power failure, so the water does not boil. This normally means a UPS - lots of cost. Actually a fire wiath a back boiler will probably never pay back the investment in it.
Wood boilers are avaiable we have a Extraflame Ecoligia Idro sat waiting commissioning, which the fire burns when hot water is demmanded by the heat store, and runs on wood pellets made from scrap wood.
You will already have a link through your central heating thermostat, why bother with another? Especially as it is likely to be very expensive! If you link your stove to your central heating, then it has to gravity feed your hot water, and you will probably require another feed/expansion tank in the loft. Is your tank more or less directly above the stove?
What makes you think that a water jacket makes the stove efficient? They make the stove less efficient! Your gas system gives you automatic control over everything. You could always switch it to water only, and "centrally heat" your house with a dry stove.
I seriously doubt that what you are suggesting will pay for itself. Gas is cheaper than wood after all. Those who do not heat their houses with wood will doubtless chime in at this point that wood can be free. Don't listen to them, they are idiots.
I seriously suggest that you spend the thousands of pounds you would have spent on neutralisers or thermal stores on insulation. Enjoy a dry stove for what it is, a beautiful and powerful heat source. Open some doors and let the heat spread through your house!
You can't put any obstructions in the heating route of the solid fuel boiler - the pump might fail or suffer a power cut; there may be a way round this but I never found it.
You pump from the oil/gas burner to the DN and then a second pump to the CH or DHW.
I think experience would direct me to siding with those who suggest a dry stove would be better economics. I put in a wet stove some 25 years ago to drive the CH/DHW system on its own - I was young enough then to cope with the log processing then. The problem was that the stove had to be driven hard to supply the water heat and correspondingly overheated the room it was in and it never really supplied enough water heat.
In due course I found a suitable oil burning boiler and fitted that and the Dunsley Neutraliser - it may be now that dual heating coil tanks , heat stores, etc would be better but at a considerable cost. The Neutraliser works extremely well and does exactly what is asked off it; it is also quite small and doesn't involve replacing the DHW tank. It is a very effective 'poor man's' solution !!
Although I can recommend the Neutraliser as the solution to getting water heat out of a solid fuel boiler, I would agree with others, and I do talk from20+ years experience, that it is an expensive route and involves a significant upheaval to the plumbing with a poor return financially.
Also do not go multi-fuel - a small dedicated wood burner matched to the room size would be my recommendation; kinder on the pocket in initial outlay, better space usage in the room and far less upheaval in fitting.
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