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 www.heatweb.com
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
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
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.
Come back if you want any more info.
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
Have 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.
Yes and yes.
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 thought it was no obstructions between cold feed into boiler and hot
outlet with vent to F&E tank. This can accommodate a pumped supply to
boiler but if the boiler has a high flow resistance then pump over to
F&E tank becomes a problem.
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
Dave. pam is missing e-mail
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.
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).
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!
I do have a free supply of wood logs from the local golf club, they
usually make bonfires of these as it costs to tip them.
Started this thread after reading a previous thread discussing a
report on comparative fuel costs and carbon emissions from the The
Solid Fuel Technology Institute link below
It has wood logs at the lowest cost and carbon emissions, it just go
Talking of which, is there any way of using chipper output for heating? A
tree surgeon uses a nearby field to store the results of his surgery and
there must be 50 tonnes of the stuff. he gives it away, and occasionally
gets the farmer to spread it on the fields. Surely there's a better use
than that (we take a small amount for use as mulch)?
Ignorance more frequently begets confidence than does knowledge: it is those
who know little, not those who know much, who so positively assert that this
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