Kevin G wrote:
I'm guessing there is a formula to be used when
calculating heat loss? The problem is, I don't know if I would
adequately be able to plug variables into a formula because there are
a few windows in the garage, an interior door, etc.. This would
probably be something I would have to pass along to my contractor.

Any suggestions on figuring this out?

It is relatively trivial to run a quick "Manual J" calculation for your
purpose.

Here's an online calculator that will probably get you close enough.
You can also Google on "Manual J" for more technical details and other
calculators.

http://www.mrhvac.com/index.html?htt...nualjshort.htm