overextended periods of time below the low 70's in temperature can bring on a cold - we're talking several hours, every day, for days to weeks.
Other than that, anything you can stand should be fine, considering you have normal heat to keep you healty.. if it is 40 degrees in there, obviously not.
Another thing to remember is that your body is 97 degrees - very warm.. no matter how cold your room were, your boa would love to me ON you, probably even moreso than in his cage!
My ambient room temps can sometimes get as low as 65 or so if i'm working and have the doors open, but I won't leave them out in that condition.
I receive lots of animals shipped in the winter to me very cold, and I usually hold them or leave them on me for a while to warm up... quickest way i've found.
Hope this helps..
Joe Rollo - BciJoe
-----
Thanks and take care - Joe Rollo
'Tis not the stongest of the species that will eventually survive, nor the most intelligent, but the one most responsive to change' Charles Darwin