Tom,

You've stumbled onto one of the items that needs to be updated in the next version of E-Quest. The F-factor is not the same as the U-factor you've indicated on the attached document. The way to correctly account for the heat loss through the slab perimeter is to correlate the F factor to an equivalent U value for input into the program. Take a look at the 2009 ASHRAE fundamentals Chapter 18.30-32 equations 35, 41, and 42 for how to do this. Inputting the F-factor directly for the U value could greatly skew the heat loss that occurs through the slab.

Sincerely,

Michael Daley, PE