Remember with any crack "or larger" that lets in cold air, you are fighting a losing battle up there where it gets cold...
I had a shop in North Mo before I went to SW Mo that was about 30 x 60, insulated with bats and sheetrcock walls and ceiling. A small $200 wood stove would run you out once it got going, but till then if was cold as the thermometer said!!! It had hardly any draft anywhere.
I nothing about HVAC except that out home 3 ton unit was old and it bit the dust late last summer. Hey Doc can you contribute a few grand for the new one!!??? Tax write off charity contribution!! They are silly expensive, like 15 times a root canal!!!! OK at least 10 times!
