I think I've been misunderstood here.  I want to keep bees in hives for all of
the benifits that are derived from bees.  The greenhouse has no pollination
problem and was only wanting to winter them in the greenhouse.  My thinking is
that the protected climate would help new colonies get established easier.  On
sunny days in the winter, I could feed them and when placed outside in the
spring, they would have a head start.
I see the point of bees not getting back into the greenhouse via vents and it
would not bee very hard to modify the greenhouse to have a hive entry on an
outside wall.
Thanx for the responces
Richard