contact a few companies that sell walk-in refrigeration equipment. give them the details of your box and they can run load calculations to tell you what size system you need. they'll ask you the appropriate questions and run the numbers through a computer program to figure out how much BTU you need.
just make sure you get quotes from a few different companies to make sure they all come to the same conclusion. the first people i talked to sold me a 1HP for my walk-in, but after the installer said he thought it was too small i called 3 other places and they all agreed a 3 HP was needed.....live and learn....
hey look, post # 100! do i win anything for that
Blank Slate Brewing Company