hi. I've got an attached garage with a couple of plug-ins, an overhead
door, and a couple of lights. I want to use the garage as a shop.

I've purchased a forced-air furnace for the garage, and want to run
some new electrical for it. The house was built in the 1960s, and I
have an existing 100 Amp service. It appears that the garage shares
some circuits with part of the basement.

I also want to have 220V available while I'm at it.

My thought is to run 8/3 wire from my existing panel to the garage
(approx. 40'), and then run a sub-panel from that. does that sound
reasonable? What amperage breaker would I use?

Thanks in advance for any help.