Temperature loss during degassing

We're upgrading our tank degasser and I'm trying to develop a thermal model.
Can anyone tell me if the temperature loss during the initial pump down to
two mm of pressure has a higher loss rate than when the heat is at a
pressure of < 1 mm? I would think you lose more temperature during the
initial out-gassing, but I don't know this for a fact. The only thing I do
know is the temperature loss during the total degas cycle. We take a temp
before and after degas. However, we want to be able to predict our
temperature losses, based on the degas process, so we have better control of
our casting temperatures.
I certainly appreciate your help, and if you have any other recommendations,
please let me know.
Thanks
Lloyd Hanning