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I've never had to deal with a situation like this, but let's get all of our ducks in line.
From what I gather we have an approximate r-value between the basement space and the steam pipe of about R-20. Let's check the math:
12" concrete around steam pipe @ R = 0.08/inch = 1.0
12" concrete walls of the vault @ R = 0.08/inch = 1.0
Air space between the insulate steam pipe and the wall of the vault = Approximately 0.8
30" of soil between the vault and the foundation wall @ R = 0.5/inch = 15
24" of fieldstone foundation wall @0.09/inch = 2.16
Total approximate R value = 20
Now, let's take a look at the layout of the walls.
You have 1728 square feet of total wall space in the basement and, of that, we have 126 square feet of vault wall space that lies in-line with the basement wall.
Does this sound right so far, William?