[Cob] wood stove--- heads up

[Shannon C. Dealy]

On Thu, 26 Aug 2004, Bill&Julie wrote:

> If you design a stove to heat your whole house, and be efficient at -20°f,,
> Then any temperature above that you will have to throw away energy.
>
> By that I mean, cooling the fire by closing the draft, allows smoke to
> go up the chimney unburnt..All smoke that is HOT enough will burn...

This is only true of conventional wood stoves, it is not true for any mass
stove design including the rocket bench stoves, these stoves only run at
the maximum efficiency which they are capable of, and rely on the thermal
mass to regulate the temperature, they do not have a damper, and
their heat output while operating is not intended to be adjusted by
damper and air intake settings, you simply fire them more or less
often, and for shorter or longer periods in order to regulate the
temperature.

[snip]
> In Northern Minnesota,, the trend is towards the OUTSIDE FURNACE..
> The beauty of these is to leave the draft open until the wood is gone,
> allowing enough air to combust all of the fuel at a high temperature.
> Trapping the heat in a well insulated water jacket, and then pumping
> the hot water into the house as needed for what ever warmth that is needed.

This is exactly what the bench stove design does except it dumps the heat
into a bench made of rock and cob which can store more heat than water
per unit of volume, though of course it's a little hard to pump the cob
around your building to move the heat :-)

> Back to the bottom line,,, did Granddad survive in his 50% efficient house?
> Must we spend tens of thousands dollars to save a few hundreds???
> Find a good design, and use it... Don't worry if your 83% system is not
> as good as some guys 84.5% system..
[snip]

While an efficiency difference of 1.5% may not be worth worrying about
every bit makes a difference, and the difference between different wood
heating systems can run more like 50% to 75%, and this translates into
alot more work and/or money for heating each year, just a 10% difference
in efficiency means you need 10% more wood and must run the fire 10%
longer.  There are of course also environmental issues to consider,
deforestation, and even if both stove designs burn 100% of the fuel and
the difference is only in heat extraction efficiency, you are generating
10% more carbon dioxide (a greenhouse gas).  Of course the cob bench
design can be built for under $100 (depending on your scrounging
capabilities) and give you the maximum efficiency at the same time.


Shannon C. Dealy      |               DeaTech Research Inc.
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