Hi Jennifer,

Nice to hear from you! While honey bee colonies will often use an upper entrance throughout the winter on warmer days for cleansing flights or even early season foraging, it's not completely necessary to have an upper entrance. Sometimes colonies overwinter when upper entrances are blocked by snow. Some commercial beekeepers overwinter their bees in sheds where the temperature is set so that bees don't exit the hives.

There are a lot of configurations in which honey bee colonies can survive the winter, including ventilating hives and condensing hives. My understanding of Bill Hesbach's description of the condensing hive is that an upper entrance negates his system of moisture control. 

Here is an article on condensing and ventilating hives: Ventilating vs. Condensing Winter Colony – Willamette Valley Beekeepers Association (wvbahive.org)

Here is a video in which Bill Hesbach explains condensing hives: Bill Hesbach, 2/14/2021 - YouTube

Here are some examples of how the University of Minnesota Bee Lab winter colonies, which involve upper entrances: Wrapping Honey Bee Colony for a Northern Winter and Wrapping Honey Bee Colony for a Northern Winter with Tar Paper.

Overall, the most important components to overwintering seem to be making sure that colonies go into winter with low virus and varroa loads and they have sufficient honey/food. 

Happy beekeeping!