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factsheet
wood
stoves |
what
are they?
They are stoves for burning wood to heat your space, your water,
and even to cook on. A basic stove will be of cast iron or steel
(lined with fire-brick to retain heat), usually with a door at the
front for loading, lighting and ash removal – but sometimes
on top in small stoves.
Open fires are pretty, but most of the heat disappears up the chimney.
Also, updraughts from below pass through the logs and draw off volatile
gases (which provide most of the heat) and suck them up the chimney
unburnt, which wastes heat and causes tar build-up in the chimney.
The casing of a stove heats up and radiates heat out into the room.
You can have a simple stove for heating, or one with a back boiler
to provide hot water / central heating.
Ceramic stoves or kakkelovns (popular in Scandinavia and Eastern
Europe) have a ceramic casing that acts as a heat store to radiate
heat into the room for hours after the fire is out. These are much
more expensive than standard log burners. Aga / Rayburn-type cookers
are also much more expensive than a basic stove, and nowadays tend
to be fuelled by gas, oil or electricity.
Pellet stoves burn pellets made of compressed organic material such
as sawdust or agricultural plant waste, and can be automatically
fed from a hopper.
Larger automatic-feed wood or pellet boilers can be installed in
schools, hospitals etc.
what are the benefits?
CO2
is the most important greenhouse gas; wood is a carbon-neutral fuel
in that burning releases CO2 (the same amount
as if the trees died and rotted) but new trees absorb it. Growing
trees absorb more CO2 than mature trees, so
as we harvest mature trees, from a climate change perspective, it
is essential that we replace them with new ones. Wood is a renewable
resource that provides a habitat for wildlife. It also has a good
energy balance, i.e. can be locally produced, requiring very little
processing or transport energy (logs more so than pellets, although
pellets release less of the pollutants that cause acid rain).
Emissions are better than coal, oil or gas as regards NOx and SOx
(acid rain) and carbon monoxide but worse for particulates. For
space heating, emissions and energy losses from power stations make
electricity the worst option environmentally; and wind and photovoltaics
are as yet too expensive for heating.
Modern ‘clean burn’ stoves can be used in smokeless
zones; they use secondary combustion, baffles or catalyts to maximise
combustion of gases and particulates, reducing emissions and increasing
efficiency.
what
can I do?
stoves: basic stoves start at around £400,
(c. £1000 for clean burn) new,
or cheaper second-hand.
If you have access to sheet steel, and cutting and welding equipment,
you could even build your own, which would work out cheaper still.
Your supplier should be able to recommend an installer, or you can
install yourself: stand the stove on a slate or concrete slab (not
too close to wooden fire surrounds), make a metal plate for the
chimney (can be a thin sheet of stainless) with a hole for the flue
pipe (‘Copex’ is useful because it’s flexible),
seal flue and plate with fire cement, put fire string round door
(both from plumbers’ merchants or online – see 'resources'.
Old chimneys will need re-lining, as tar could be deposited, causing
a fire hazard, plus gases could seep through into living areas.
Chimneys must be swept every year to remove creosote and tar and
avoid chimney fires.
wood: 5 tonnes of wood per year is more than enough
for a basic stove in your main living area – but that’s
assuming it’s in use most of the time from October to April;
unseasoned wood is heavier because of the water content. Logs are
the cheapest way of heating your space – around 1/5 the price
of electricity per kWh. It will probably get relatively cheaper
too, as fossil fuel prices rise, and carbon-neutral fuels get tax
breaks.
You can buy logs split, or cords (lengths over 1m) and cut and split
them yourself, in which case you’ll need a chainsaw and a
splitting axe from a farm / garden equipment supplier (ask about
protective clothing and health & safety). Trees are best felled
in the winter when moisture content is lower, then cut and split
to dry better. Store under cover for at least one summer, which
should reduce moisture content to around 25%.
Ash is probably the best firewood, as it has the lowest moisture
content when green (c. 35%), but beech, cherry and hawthorn are
also good. Don’t use second-hand construction timber, unless
you’re absolutely sure it’s untreated, as it will release
toxic fumes; and certainly not chipboard, plywood or mdf –
even for kindling – as it contains formaldehyde.
Bring some split logs in and stack them next to the stove (not touching)
– this will dry them more. Leave a layer of ash at the bottom
of the fire, add paper, dry kindling (you don’t need firelighters)
followed by a few small, dry logs. There will be an air inlet to
adjust air flow – have this open at first, and slowly shut
it down as the fire becomes more established.
Wood ash contains potash, and can be used as a fertilizer (best
applied at the end of the growing season, and not on alkaline soil).
resources
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more
- information, books, courses, suppliers, links etc. |
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printable version
of this factsheet (pdf)
a basic woodstove
with logs stacked next to it, plus waste paper for lighting the
fire, and a copper kettle on top for making tea
a
home-made saw-horse, on which you can chainsaw cords (lengths of
timber) to the right length to fit into your wood stove
you will
need to cut kindling from waste wood, twigs, unwanted furniture,
doors etc to help light the fire; it needs to be very dry, and can
be kept in a basket near the stove to dry it further
stacking
the split logs under cover for at least one summer will reduce the
moisture content to around 25%
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