Does anyone have any recent experience of specifying a small woodburning
"wet" system - say 5kW woodburner with 2kW to room and the rest to hot
water/radiator(s).

I could fit one using a redundant kitchen chimney, but I estimate my
kitchen only needs 2kW - so it would be useful/necessary to divert the
rest of the heat elsewhere. However the cost/complexities of a "wet"
system seem to make the whole project "too expensive / too difficult".
For example a dual coil hot water cylinder will cost several hundred
more than the standard item.

I currently have a log burner in my lounge which (with internal doors
open) heats about 2/3 of my bungalow. The aim of an additional stove
would be to further minimise the use of gas central heating. My
economic case makes assumptions about burning my own wood - in my
experience logs bought commercially cost more per kWhr than gas at its
present price - in fact they track the price of other fuels!

Any comments/ experiences?

Andrew

"Andrew" wrote in message
o.uk...
Does anyone have any recent experience of specifying a small woodburning
"wet" system - say 5kW woodburner with 2kW to room and the rest to hot
water/radiator(s).

I could fit one using a redundant kitchen chimney, but I estimate my
kitchen only needs 2kW - so it would be useful/necessary to divert the
rest of the heat elsewhere. However the cost/complexities of a "wet"
system seem to make the whole project "too expensive / too difficult". For
example a dual coil hot water cylinder will cost several hundred more than
the standard item.

I currently have a log burner in my lounge which (with internal doors
open) heats about 2/3 of my bungalow. The aim of an additional stove
would be to further minimise the use of gas central heating. My economic
case makes assumptions about burning my own wood - in my experience logs
bought commercially cost more per kWhr than gas at its present price - in
fact they track the price of other fuels!

Any comments/ experiences?

The ratings given for wood burners are max, ie with a roaring inferno
inside, not practical or neccessary.
Try to get a room sealed one ie with an air pipe coming to the stove from
outside.
Avoids drawing cold air into the room hence much more effective
http://www.stovesonline.co.uk/external-air-stove.html

harryagain wrote:

The ratings given for wood burners are max, ie with a roaring inferno
inside, not practical or neccessary.


I do understand however that woodburners are most efficient when working
towards the top of their output ranage - and that continual use on a low
setting increases the production of pollutants/creosote which is
damaging to the flue.

Andrew

"Andrew" wrote in message
o.uk...
harryagain wrote:

The ratings given for wood burners are max, ie with a roaring inferno
inside, not practical or neccessary.


I do understand however that woodburners are most efficient when working
towards the top of their output ranage - and that continual use on a low
setting increases the production of pollutants/creosote which is damaging
to the flue.

Andrew

A lot depend son the design of the stove. Creosotes etc are caused by
unburned distillates condensing in the chimney.
Wet wood makes things worse.
Modrn stoves have this problem much reduced, there are two zones in the
stove, the pyrolising zone (where the wood is broken down) and the
combustion zone where the resulting vapours are burned off as a separate
process.
A bit here on the topic.
http://en.wikipedia.org/wiki/Wood-bu...olysing_stoves

Most of these pellet stoves have the two separate zones.

On Thu, 22 Aug 2013 17:31:28 +0100, Andrew wrote:

Does anyone have any recent experience of specifying a small woodburning
"wet" system - say 5kW woodburner with 2kW to room and the rest to hot
water/radiator(s).

I think you will struggle to find that combination and possibly a
boiler model that small. We have a Stovax Stockton 11. Nominal 11 kW
total with 3 kW to the room.

However the cost/complexities of a "wet" system seem to make the whole
project "too expensive / too difficult". For example a dual coil hot
water cylinder will cost several hundred more than the standard item.

Why do you need a dual coil cylinder? The stoves boiler shares water
with the gas boiler CH circuit. All you need is a "Dunsley
Neutraliser" or similar where all the flow/returns meet and mix at
the same level and thus pressure. This stops the pumps circulating
water via the stove when it's not hot. The DN needs to be above the
stove so gravity can circulate the water and with only a low thermal
capcity DN it might be wise to have a dump radiator across the
gravity loop with a passive thermostatic valve that opens at around
85 to 90 C.

Our stove is linked into a 300 l thermal store also heated by solar
and oil. I reckon the stove saves about 1000 l of oil over the 6
month winter period mid October to mid April. Lighting the stove
about 1500 and keeping it going with a good burn through to about
2200. Note that is roughly 7 kW to water rather than 3.

... in my experience logs bought commercially cost more per kWhr than
gas at its present price - in fact they track the price of other fuels!

I'd agree with that. Buying seasoned hardwood logs at £75/dumpy bag
(approx 500 kg) the cost is comparable to oil. Oil is around 6p/kWHr.
Last time I paid a mains gas bill it was about 3p/kWHr but thats
nearly 15 years ago...

--
Cheers
Dave.

On 22/08/2013 20:58, Dave Liquorice wrote:

Why do you need a dual coil cylinder? The stoves boiler shares water
with the gas boiler CH circuit. All you need is a "Dunsley
Neutraliser" or similar where all the flow/returns meet and mix at
the same level and thus pressure. This stops the pumps circulating
water via the stove when it's not hot. The DN needs to be above the
stove so gravity can circulate the water and with only a low thermal
capcity DN it might be wise to have a dump radiator across the
gravity loop with a passive thermostatic valve that opens at around
85 to 90 C.

Fascinating, never come across them before.

newshound wrote:
On 22/08/2013 20:58, Dave Liquorice wrote:

Why do you need a dual coil cylinder? The stoves boiler shares water
with the gas boiler CH circuit. All you need is a "Dunsley
Neutraliser" or similar where all the flow/returns meet and mix at
the same level and thus pressure. This stops the pumps circulating
water via the stove when it's not hot. The DN needs to be above the
stove so gravity can circulate the water and with only a low thermal
capcity DN it might be wise to have a dump radiator across the
gravity loop with a passive thermostatic valve that opens at around
85 to 90 C.

Fascinating, never come across them before.

Yeah, they're the expensive alternative to having a thermal store.
Hideously overpriced.

--
€¢DarWin|
_/ _/

On 22/08/2013 20:58, Dave Liquorice wrote:
On Thu, 22 Aug 2013 17:31:28 +0100, Andrew wrote:

Does anyone have any recent experience of specifying a small woodburning
"wet" system - say 5kW woodburner with 2kW to room and the rest to hot
water/radiator(s).

I think you will struggle to find that combination and possibly a
boiler model that small. We have a Stovax Stockton 11. Nominal 11 kW
total with 3 kW to the room.

However the cost/complexities of a "wet" system seem to make the whole
project "too expensive / too difficult". For example a dual coil hot
water cylinder will cost several hundred more than the standard item.

Why do you need a dual coil cylinder? The stoves boiler shares water
with the gas boiler CH circuit. All you need is a "Dunsley
Neutraliser" or similar where all the flow/returns meet and mix at
the same level and thus pressure. This stops the pumps circulating
water via the stove when it's not hot. The DN needs to be above the
stove so gravity can circulate the water and with only a low thermal
capcity DN it might be wise to have a dump radiator across the
gravity loop with a passive thermostatic valve that opens at around
85 to 90 C.

How would that work? If all ins and outs are at the same pressure, then
flow would be only dependent on resistance?

The way I've done it for 2 gas boilers is to have a pump and a
non-return valve for each boiler.

On Fri, 23 Aug 2013 01:04:14 +0100, Fredxx wrote:

All you need is a "Dunsley Neutraliser" or similar where all the
flow/returns meet and mix at the same level and thus pressure.
This
stops the pumps circulating water via the stove when it's not hot.

How would that work? If all ins and outs are at the same pressure, then
flow would be only dependent on resistance?

No pressure difference between an in and out on a given loop means
there will be no flow in that loop. CH/DHW loop has pump to circulate
the water and stats to control a motorised valve to direct the flow.
The gas boiler loop also has a pump. The stove loop is just gravity.

The way I've done it for 2 gas boilers is to have a pump and a
non-return valve for each boiler.

Gas boilers are very controlable, turn it of it goes off. A stove is
not so easy to turn off. The heat loop needs to be open and a heat
dump rad connected by a passive thermostatic valve. ie one like a wax
TRV, not an electrical thermostat and motorised valve.

As the OP is only looking at 3 kW to water it might be simpler just
to have a good sized radiator on the landing up stairs that is only
connected(*) to the stove boiler and leave bedroom doors open to
distribute the heat. The normal room stat on the CH system will hold
the gas boiler off if the place is warm enough.

(*) *NOT* sealed this needs to be an open vented system with
feed/expansion tank and feed/expansion pipes somewhere.

--
Cheers
Dave.

Dave Liquorice wrote:

As the OP is only looking at 3 kW to water it might be simpler just
to have a good sized radiator on the landing up stairs that is only
connected(*) to the stove boiler and leave bedroom doors open to
distribute the heat. The normal room stat on the CH system will hold
the gas boiler off if the place is warm enough.


Not easy to explain complicated situation in a few words - but this is
the root of my problem. It would be simple to just add a heat leak
radiator in a hallway to dump the extra heat, which would then find its
way into the bedrooms. But I live in bungalow, and without major
building work the only suitable location in the hallway for gravity feed
is just 450 mmm wide, necessitating a tall thin radiator. Even this is
awkward as it would obstruct the full opening of an internal door.

The bathroom is another possibility - but it is very small and would
result in some awkward arrangement of a radiator directly above the bath.

Plumbing into hot water cylinder would be easy (if costly), but I recon
my annual hot water costs with gas are not much more than £100 - and the
use of a stove will not always co-incide with hot water needs. Also
these days it is increasingly difficult to avoid heating water by
electricity - practically no washing machines or dishwashers have a hot
fill.

The cost of gas is of course very non linear if one only uses a small
amount due to standing charges/ increased unit rate on the first units
in lieu of standing charges.

Andrew

On Fri, 23 Aug 2013 16:36:39 +0100, Andrew wrote:

As the OP is only looking at 3 kW to water it might be simpler
just
to have a good sized radiator on the landing up stairs ...

But I live in bungalow, ...

Ah, that does make it more complicated and could well make a boiler
option on the kitchen stove a non-starter.

The neutraliser needs to be above the stove and not far from it
horizontally, the CH/DHW flow/return and the boiler flow return also
need to be connected to it (and the volume of the neutraliser forming
part of each circuit) but as they are pumped getting circulation
through them isn't a problem. The heat dump rad is.

TBH seems like a lot of work for very little benefit. 3 kW isn't a
great deal in space heating terms.

I wonder if just installing a small stove, sans boiler, and leaving
the kitchen door open would be just as effective at reducing the gas
bill.

Plumbing into hot water cylinder would be easy (if costly),

You don't need a double coil cylinder or even a replacement
cylinder. All you need is a Dunsley Neutraliser or functional
equivalent. DNs are fing expensive for what they are, a water tight
box with lots of pipe connections (6 in your case).

but I recon my annual hot water costs with gas are not much more than
£100 - and the use of a stove will not always co-incide with hot water
needs.

This is very true it can be offset by using a thermal store but for
just 3 kW of occasional/intermittent wood burner it's probably not
worth going down that route. Starts getting more interesting if you
add solar thermal. The solar thermal and the 300 l store here save
about 10 l oil/week in the summer period or about £150 at 60p/l.


The cost of gas is of course very non linear if one only uses a small
amount due to standing charges/ increased unit rate on the first units
in lieu of standing charges.

If you are a low user take a look at Equipower/Equigas. No standing
charge at all (not even the "hidden" one with high priced first x
units). You pay only pay for what you use, slighly higher rate than
the cheapest standing charge tarrifs out there but not stupidly
expensive.

--
Cheers
Dave.

practically no washing machines or dishwashers have a hot
fill.

What you can do is run a thermostatic mixer valve with a return loop and
pump provided you have a hot water cylinder.

Basically run three pipes to the TMV and the TMV must be as close as
possible to the washing machine/dishwasher.

One pipe will obviously be cold, the 2nd will be hot, and the third pipe
is the hot water return via a small pump immediately before it enters
the hot side of the TMV.

This small pump can be a 12 volt job powered by a solar panel and
rechargeable battery.

Set the TMV to the desired temperature infact, you probably can get away
with setting the temp 10 degrees higher to account for teh thermal mass
of the washing machine/dishwasher.

When you want to use washing machine or dishwasher, start the hot water
return loop pump on. As soon as the hot water and hot water return pipe
is piping hot, the start the dish washer/washing machine.

As soon as the cycle has finished, switch off the hot water return loop
pump.

Less electricity will be used to heat the water and the washing cycle
will be shorter as a result. Gas is 1/4 of the cost of electricity for
heating water (assuming condensing boiler, or would be even cheaper if
you have free wood.

Dave Liquorice wrote:


I think you will struggle to find that combination and possibly a
boiler model that small. We have a Stovax Stockton 11. Nominal 11 kW
total with 3 kW to the room.

Your comments are much appreciated.

I was thinking perhaps in terms of a Clearview Pioneer 400 - 5kW with
approximately half of that to hot water

Andrew

Andrew wrote:

Any comments/ experiences?

I've done this more than once. A thermal store with a coil for gas/oil
boiler on a sealed system is the best way to do it. Not cheap.

I'm about to do it all over again with a 16kw stove, I have an
inexhaustible supply of wood and gas is expensive.

Manufacturers estimates for stoves and the split between hot water and
space heating are always optimistic. I'm unconvinced that any installation
puts more heat into the water than it does into the room.

--
€¢DarWin|
_/ _/

Steve Firth wrote:

I've done this more than once. A thermal store with a coil for gas/oil
boiler on a sealed system is the best way to do it. Not cheap.

I'm about to do it all over again with a 16kw stove, I have an
inexhaustible supply of wood and gas is expensive.

Manufacturers estimates for stoves and the split between hot water and
space heating are always optimistic. I'm unconvinced that any installation
puts more heat into the water than it does into the room.

Thank you for your insights. I think this sums up my dilema. My
existing woodburner in my lounge provides about 2/3 of my heating
requirements. Therefore installing another one to cover the remaining
requirements gives rise to dimishing returns - unless it is straightforward.

My other limitation is how much heat can be output in kitchen - and as
you say the manufactures split between hot water and space heating is
probably optimistic.

Andrew

On Fri, 23 Aug 2013 11:22:35 +0000 (UTC), Steve Firth wrote:

Manufacturers estimates for stoves and the split between hot water and
space heating are always optimistic. I'm unconvinced that any
installation puts more heat into the water than it does into the room.

I agree the figures are a bit "vague", having said that ours seems to
match the nominal 3 kW to room and 7 kW to water. IIRC the heat calcs
for the room indicated about 2.5 kW. With the stove buring well all
evening the room is "toasty" but not over heated. And you can see the
store temp climbing fairly quickly when the CH is not calling for
heat.

The 38 kW oil boiler will raise the store from 60 to 70 in about 20
mins, the solar (suposidly about 3 kW) will take most of a bright
sunny day say 6-8 hours, the stove is between the two maybe 3 hrs,

--
Cheers
Dave.

Andrew wrote:
Does anyone have any recent experience of specifying a small woodburning
"wet" system - say 5kW woodburner with 2kW to room and the rest to hot
water/radiator(s).

I could fit one using a redundant kitchen chimney, but I estimate my
kitchen only needs 2kW - so it would be useful/necessary to divert the
rest of the heat elsewhere. However the cost/complexities of a "wet"
system seem to make the whole project "too expensive / too difficult".
For example a dual coil hot water cylinder will cost several hundred
more than the standard item.

I currently have a log burner in my lounge which (with internal doors
open) heats about 2/3 of my bungalow. The aim of an additional stove
would be to further minimise the use of gas central heating. My
economic case makes assumptions about burning my own wood - in my
experience logs bought commercially cost more per kWhr than gas at its
present price - in fact they track the price of other fuels!

Any comments/ experiences?

Andrew

Thanks to everyone who has contributed to this thread. My conclusion is
that installing another woodburner is probably too much effort for an
uncertain gain.

What is interesting is that when the bungalow was originally built in
the early 1960's there would have been a solid fuel stove for hot
water/radiators in the kitchen, which presumable did not give out too
much heat. But in those days there would have been no double glazing,
cavity wall insulation, or sensible amount of loft insulation. I am
also suspect the single pipe central heating (now pumped - and about the
be replaced) was originally designed for gravity circulation, but no
doubt in those days there were different expectations about both warmth
and system safety.

Andrew