"nbaxley" wrote:

I have a 20'x30' old shed that I'm turning into a office/workshop.
The office will occupy a 8'x15' corner of the workshop and be walled
off and insulated from the rest of the workshop. I was given a fairly
large wood burning stove by an uncle and I'm wondering how best to use
it to heat both office and workshop... Right now I have no insulation...

Wood is work. More insulation means less work...

...This is in central Illiois so the winters can get pretty cold.

NREL says Peoria is 27.0 on an average December day, with a 34.6 F
average daily max... 830 Btu/ft^2 of sun falls on a south wall.

The roof is a fairly flat slant and pitches to the north only, it's
just a one-way slant whatever that's called...

Maybe you have a 10'x30' south wall. With a layer of polycarbonate glazing
(about $1.50/ft^2 in 4' wide rolls, with a 10 year guarantee), you might
collect 0.9x830 = 747 Btu/ft^2 and lose 6h(80-31)1ft^2/R1 = 295, for a net
gain of 452, or 135.5K Btu for the wall. You could keep the shed 65 F for
8 hours if 135.5K = 8h(65-31)G, ie if the shed's thermal conductance G
= 498 Btu/h-F or less. G = 900 ft^2/R makes R = 1.8. Not much :-)

2) Can I distribute the heat by routing the exhaust pipe through the
building...?

LCZ wrote:

I wouldn't be running exhaust pipe all over just for the heat it produces.
You want a good 'draw' on the stove to get it operating at its best.

That might come from Grainger's $80.55 4C941 450 F 136 cfm blower with
their $16.38 4WZ05 speed control pushing cooled flue gas up a chimney.

...you need it above the roof line to get a good draw.

A forced draft might go out a window...

I put a damper on the pipe just above the stove. Between this and the air
intakes on the doors of the stove I could control the heat very well.

You might control the heat with a thermostat (eg Grainger's $13.25 2E158)
that turns off the draft blower when the room's warm enough. Another in
series might turn on the blower when the stove is hot.

So long as you don't need a natural draft, why not suck more heat out of the
fluepipe? The draft blower might be near the outdoor chimney connection (if
any) and its long 6" fluepipe could draw air from the stove outlet. Meanwhile,
the middle part of the fluepipe could be inside a 10" pipe with a T and a 10"
to 6" reducer at one end to make an air-air heat exchanger. The T could be
mounted horizontally near the chimney, with Grainger's $70.85 4C847 550 cfm
10" fan at the far end (also controlled by the room temp thermostat) pushing
room air into the T, through the space between the inner and outer pipes.
The room air would emerge warmer from the end near the stove.

Meanwhilst, the flue pipe would slope towards the chimney, and flue gas would
enter the blower from the 6" vertical pipe below the T, via an elbow with a
pinhole to let condensation drip into a bucket and exit the blower into the
outdoor chimney connection at X. A condensing chimney might produce at least
15% more useful heat than one without, with the same wood consumption.

The setup might look like this, in a fixed font like Courier:

10" pipe ______________________________
___________________________ f
6" pipe / -------------------------- \ == a
|| ----------------------\||/----n --------
|| 10" elbow -- ||_________| X |
|| \ -- blower |
|| \---------|________|
|| |-- L --|
---------
draft | |
inlet-- | stove |
--------- | drip |
| | |bucket|
-----------------------------------------------------------------

If 20 cfm of 600 F flue gas enters the L' fluepipe and the fan pushes 400
cfm of 70 F room air into the 10" pipe, and we want the exiting flue gas
temp to be 212 F max, E = (600-212)/(600-70) = 0.73. Z = Cmin/Cmax = 20/400
= 0.05 and E = (1-e^-(1-Z)NTU))/(1-Ze^-(1-Z)NTU)), so NTU = 1.347 = AU/Cmin,
= 3.14L/20 in this counterflow heat exchanger, and L = 8.57 feet, or less,
with condensation in the inner pipe.

L = 10' would be convenient.

Nick