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. The office will be my home
office and will house a couple of computers a desk and a couch. Right
now I have no insulation and no walls put in and the stove is sitting
in the corner not hooked up so I'm not fettered by any existing
construction. I will be insulating the walls and the ceiling
eventually. A couple of other factors. This is in central Illiois so
the winters can get pretty cold. The roof is a fairly flat slant and
pitches to the north only, it's just a one-way slant whatever that's
called. There is a big sliding door on the east side that I'm not
quite sure how I'm going to insulate yet. Several questions:
1) Is there a certain place to put the stove to get the best
distribution. I can probably put it along the shared wall of the
office and workshop to get a central location but I don't want to have
it in the way too much.
2) Can I distribute the heat by routing the exhaust pipe through the
building? Does that put off much heat itself and are the ways to help
3) Are the are any precautions I need to take if I route the exhaust
through the drywall walls from the workshop to the office?
4) Is it any better to send the exhaust out the wall than the roof?
I'm sure there are lots of other questions I should be asking as well
so I'd really appreciate any insightes you've got.
Check the fire codes.. It can be done, but ther must be some cleaance
between the stove and wall. Even with sheetrock on the wall, it must have
some protection. There are heatshields available or you can make one.
Years ago, it was done like that all the time. Visit some historical
homes/shops and you will see pipes going horizontal for 10 or 12 feet across
Probably but I don't know the latest codes. There are shields available.
In any case it must clear the roof by a certain amount. It may be
easier/cheaper todo it one way over the other but that will depend on your
construction and particualr layout. The pipe must extend a few feet to
ensure a good draw.
You can install a vent between rooms to help heat flow. A small fan can
make a huge difference. It is also possible to have too large of a stove.
What happens is that you cannot run it hot enough and you get a creosote
buildup in the pipes and chimney. Be sure to have ways to access the pipes
to clean them. Perhaps when you buy the pipe at a good stove shop the guys
can give you some installation tips.
A 20X30 shed should be no problem for wood burner. Some of your questions
depend on local building code. Taking the pipe through the wall should
require a double wall pipe. Remember this is radiant heat. I had a medium
size wood burner in a unfinished basement 28X48 and could actually run you
out with the heat. This was in the mountains of WV, some winters hit -25.
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.
Insulate the outer walls. You can run the exhaust out the roof, or out the
wall AND then up. All stove pipe on the outside is a waste of heat. As
others said, you need it above the roof line to get a good draw.
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. If
you must build interior walls consider vents in the wall to let the heat
circulate. You could even put small fans in the vents.
These wood burners can really put out the heat. Don't put a good size stove
in a small room. You will have a room you can't stand to be in.
As I stated this is radiant heat so keeping the stove as far from walls as
possible give you the benefit of heat from all sides of the stove. If it's
near the wall, remember to be VERY aware of combustible material in the
As you probably know the type of wood you burn will make a difference. Red
oak and white oak work great if good an seasoned. Pine burns fast. I don't
know if you have locust trees where your are. If so, be ware, locust can
burn with near the heat (btu) as coal. You can ruin a stove with locust.
Find a store for wood burners, they should answer any questions on local
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.
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 :-)
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.
A forced draft might go out a window...
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 ______________________________
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.
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