I heat about 4000sq ft of house and 2400 sqft of shop concrete floor. The normal weather use is around 100-120# per day, with the -15-20F weather with 20-40mph winds, I'm sure some days my use more than doubled.. but, the house was at 72*, and the shop floor was 55*.
The clayton stoves are not really very efficient. if you measure you chimney flue temperatures when you are burning hard, you will see that a LOT of heat is just going up the chimney.
Now, I have a LOT of experience with trying to heat old drafty houses.. one very effective thing to do is to use a piece of duct, like a dryer vent duct, or 4" pvc if it will work better or is less money. Run a duct from the outside of the house to the inlet of your blower fan or combustion air valve/flapper on your clayton. even just getting the duct within a few inches of the combustion air inlet of the Clayton will help.
Right now, with your stove roaring away, all the air that is going up the chimney is coming through your walls, around the windows and past the door seals and a lot comes through the gaps around the sills of the house sitting on the foundation.
By installing an outside air source, you will reduce or eliminate most of the huge amount of cold air infiltrating into your house from the thousands of small leaks. It really works.
My first home, a lousy-built place had aluminum sliding windows, with poor seals and no caulking, and I couldn't get to the gaps to caulk them... So I did what Smitty does.. I put clear plastic shrink film over the entire window, including the sills, out to the corner where the wall begins.. so I had a 4" air space..
I immediately notice that whenever the gas boiler fired, the plastic windows would puff up, like pillows !! The vacuum on the house created by the draw from the chimney was huge..
I used a 4" dryer duct, that flexible aluminum tubing, very easy to use, but also very easy to crush if misused.
I put a dryer vent to the outside of the house, removed the one way flapper and replaced it with a piece of 1/4" wire mesh. I ran the other end of the duct to the base of the gas boiler, where the air was pulled in to the fire.
The difference was immediately noticed, the plastic windows did not puff up hardly any. and the rooms felt warmer too. I had had cold air being pulled through the wall outlets, and that was mostly gone. .
That is a quick help for your situation.
But what will really do the job, is to remove whatever inside wall coverings you have, plaster over lath i'd guess for the age and construction of your house.. Buy the spray foam 'kits' available on the internet.. Foam-it Green in Chicago, and I think 'Tiger-Foam' somewhere in Pennsylvania. But just goggle closed cell foam..
The wonderful thing about using this foam is that it SEALS the outside wall, just spray a 1" layer of the foam over the lap-siding, it will adhere to the old dry wood, and seal all the gaps and joints.. and add an R-7 insulation factor.. the BIG thing is the infiltration. you can add unfaced fiberglass in the remaining stud-space in the walls, the drywall , and you will have an amazingly easy house to heat.
This is a lot more mess than adding a new wall, but a new inside wall will not seal out the infiltration. And adding all the extra studs is not cheap either.
Around that staircase on the outside wall?? rip down the plaster, spray foam and drywall, done. no loss of stair tread width, or other problems
Right now you can buy a case of 'great stuff' expanding foam and seal the gap between the foundation and the sills of the house.. In my current house, I had a gale being pulled through the gaps between the fieldstone foundation and the 8x8 beams that are the sills. once filled with expanding foam, the floors were much warmer, and the cobwebs didn't flap around like flags hanging from the floor logs/beams.
Seal it up, insulate where and when you can, and provide an outside air source for your coal heater.. it will make a big difference.