Maximum wood size for batch-fueled, top lit, household size cooking stoves.
This is about wood sizes for stoves that burn fire wood not wood chips, rice
hulls, or pellets, for which many TLUD type stoves are designed to burn.
Most wood fired, batch-fueled stoves like the "TLUD" and "Top Lit
Combustors" are very efficient and clean burning, but they need smaller
pieces of wood.
Being able to burn larger pieces is a benefit, because end users do not like
cutting wood down to shorter lengths necessary for the typical batch-fueled
stove.
So when considering household size, batch-fueled , top lit, cooking
stoves, should the maximum length of wood, that a stove will burn , be a
factor in rating, designing or considering the purchase of a stove.
If a stove needs I kg of wood to perform a cooking a task, you can't just
light a 1 kilogram chunk of wood it has to be cut into pieces.
Wood is cut in two directions, there is "cross cutting" across the grain,
which is usually done with a saw, this can be a problem, especially if you
have no saw! and there is the splitting of wood , the long way, or "with
the grain", this is easy.
So when considering wood size it is the length that is of concern, because
it is easy to split the wood down to the right mass or size pieces, but it
is more work to cross cut wood to get a length short enough to fit in the
burner.
The burner needs to be sized for the wood to lay horizontally because you
can't count on wood burning well when standing on end.
One way to cross cut wood, at the household level, is to split wood down to
size, that can be cut or chopped in two, with a machete, or an ax, or with a
small hand saw.
End users do not like cutting wood down to the shorter lengths necessary for
batch-fueled stoves, but batch burners take less time to tend, and they
use a lot less wood, so it is worth some time and hassle to downsize the
wood, the question is how much?
Some lengths of wood to consider.
· 5 cm or 2" long, It can take a lot of work to cut wood this short
, but chunks this size, burns well in a small stove and chunks have good
air flow up through the fuel bed for the TLUD.
· 10 cm or 4" long pieces would take less cutting and maybe the best
size.
· 15 cm or 6" long would take even less work to cut , but using wood
15 cm long pieces may be more difficult to burn in a small batch-fueled
burner.
A stove that would burn 6" long pieces would have an advantage over a stove
that needs 2" pieces to burn.
So I think fuel size should be a factor when considering the design, rating,
or purchase of a stove.
Lanny Henson
----- Original Message -----
From: <[email protected]>
To: "Discussion of biomass cooking stoves" <[email protected]>
Sent: Sunday, August 25, 2013 7:50 AM
Subject: Re: [Stoves] Cutting wood down to size for batch-fueled stoves.
[Default] On Mon, 19 Aug 2013 16:47:34 -0400,"Lanny Henson"
<[email protected]> wrote:
I know there has been some complaints about cutting wood down to the small
size necessary for batch-fueled stoves, so the longer the pieces a stove
will burn, the better. This is one area where stick burning stoves have an
advantage over batch-fueled stoves, that is with fuel length issues.
So what would be a minimum length we can ask people to cut their wood?
What is the maximum length that a batch-fueled household stove should
burn?
Interesting question, back before machine tools it was normal for
large fires to burn cordwood, the length of 4 ft (1.2m) was a
compromise for the wood to be handleable and to reduce the need to
cross cut. I imagine saws weren't generally available for forest work
and restricted to cutting wood for joinery, planking etc. doing things
that add more value. These billets would be held on andirons and fed
into a fire burning as they met in the middles to control power and
rate of burn, muck like a 3 stone fire with sticks.
Smaller fires probably used faggots, bundles of wood cut and gathered
by billhook. Commoners sometimes had the right to gather wood "by hook
or by crook" meaning small wood that could be snapped off (dead) or
short rotation coppice.
These smaller pieces could be subsequently cut with a hatchet.
When I sold firewood locally most people accepted 12" (300mm) logs and
split such that they could be picked up across the cross section with
one hand. Cutting and bagging we had to reduce the length to 7"
(175mm) and this was only easily done on a saw bench. Of course as you
get shorter lengths the waste sawdust becomes a problem as well as a
higher percentage of the wood, typically a chainsaw or circular saw
kerf is 1/4" (6mm).
Nowadays a lot of the smaller arisings go straight through the chipper
and when screened and dried make an excellent TLUD fuel.
I think Alex English managed to get woodchip dropping into his wedge
shaped natural draught modification to a side opening door on a wood
stove, using Dasifyer principles.
AJH
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