Underground you need some sort of masonry shaft (you can buy concrete
blocks in a "[ ]" shape to make a square shaft with about an 8" sq hole)
and run a SS or clay liner up that to a bit above ground level, then go
with a double-walled SS chimney up the side of the house along the other
one (or wherever you want it). That all needs to sit on a foundation
pad underground so it does not sink. Making a jog to the existing
chimney will make a huge cleanout problem, and might not be allowed.
You need to check codes wherever you live -- the fire dept and ( more
importantly) your homeowner insurance company usually have some strong
opinions about woodstoves and chimneys. I think it also needs to go
lower than where the WS flue goes in, for a lower cleanout port, so you
are going to have to dig a sizeable hole down several feet, do a pour,
build your flue, put in ports, etc.
None of this is cheap or particularly easy to do, but might be worth it
if the payback numbers work. I had a huge old Victorian house near
Boston, had a woodstove in the kitchen using the old cookstove flue that
went down to the basement (they had the cookstove in the basement back
in those days, below the kitchen). I ran the bottom cleanout to the
basement. I had to rebuild the top of the chimney where it made a jog
in the attic, line it with SS, build it up at the top to meet code,
etc. House had an oil boiler for primary heat. The last winter we were
there I only spent $500 on oil when my neighbors were doing that every
3-4 weeks or more often -- fired the stove in the evenings, set the
thermostat at 58F to keep the downstairs tolerable, and the heat from
the stove went up the back stairs to keep the upstairs comfortable
through the night. Timer turned on the boiler at 6AM for an hour to
warm things a bit until I got the stove going again, then back to 58F
for the day. I scrounged firewood here and there (it warms you twice!)
so cost of that was nothing but a coupla Saturdays a year and some gas
for the chainsaw, and one year I rented a splitter as I had a whole
maple tree to split up and that slitting maul was looking mighty
fearsome. I gave the city workers beer occasionally (leave a 6pack of
Bud on top of my trash barrels!) and they would drop off some cut-up
trees now and then when they had some good oak or maple -- saved them a
trip to the dump. The Bud was my largest annual expense.
--R
