Inches of Mercury Boiling Point of Water °F
26.45 120
27.32 110
27.99 100
28.50 90
28.89 80
29.18 70
29.40 60
29.66 50
29.71 40
29.76 30
29.82 20
29.86 10
All values are at sea level. Subtract 1 inch for each 1000 ft. above sea level

If the venturi pump can pull 28.3 inches, the temperature would have to be at least 72 degrees...so far, so good. However, the venturi pump is not very fast....like Mike said, you have to leave it pulling on the system for at least 20-30 minutes AFTER it reaches the vacuum level corresponding to the temp. If a system has been open very long, I usually pump for more than an hour....quite a chore for a venturi pump. Of course, here in Southern Arizona, we have no humidity so there is no need to evacuate.