As far as codes go, I am pretty sure you can't have duct work going between your garage and house.....(maybe I read what you said incorrectly?)Marianne said:Our first winter here, we didn't have our permanent heat in yet, so we used space heaters. Anything with a fan was sooo much better than the oil ones. (Deleted a bunch of just rambling here.. ) We had one kerosene heater just in case.... Put plastic on the walls, closed off areas of the house, etc.
Anyway, the best investment we made was a wood burning furnace. Our SIL got a used one really cheap $150?, spent $100 for a squirrel cage fan to boost the air flow. There's sits in the far side of the garage, ductwork comes thru an opening and hooks on to the existing furnace ductwork. Blows heat all over the house thru the vents. We had to do seperate ductwork, but now it heats the entire north side of our house, both stories. Ours was new, on sale for $999. What we saved that first year in electric rates vs buying firewood paid for the unit. But it's $$ and more for pipe, etc.
Just throwing out some ideas -
Are you somewhere that you have to follow codes and restrictions? If not, Mother Earth News has directions to make a wood burning stove on the cheap. I wouldn't pay to get the chimney fixed. Can you find a place to put a newish wood burning stove and then run the new chimney? The double wall pipe is really expensive, and you have to follow instructions on height, etc. But it can be done correctly by someone with basic skills. Lots of info on the web, kits available for ceiling/roof connection. You'll still have to use heaters in other rooms, but an array of fans might help, or ceiling fans pulling the air up will help move the warmer ceiling air down around the outer walls of the room. Google rocket stove. Lots of passive solar stuff at builditsolar.com that can be made on the cheap. At least you'll get some free heat when the sun is shining.
If you're not allowed those things, then what about looking for a used wood burning stove? You can buy new seals and stuff to fix them.
Our first wood stove is still here in the family room. It's steel, not as hot as a cast iron one, but I can still cook on it. The blower went out after one year, so now I use a little fan behind it that actually works better. It catches some of the heat from the black pipe, too.
Have you tried to google how to fix your furnace? We did that with our heat pump when it had an issue.