Being a father and having inherited the miserly heat "who touched the thermostat?" gene from my father, it kills me to put a big hole at the top of the hives every year. I can just imagine the warmth pouring out of there. My hives are in a breezy and sometimes windy spot. I've got a wind break behind, but to lessen the sucking power of the wind with respect to drawing the warmth out vs simply allowing the moisture to escape, I made up a small roof to go over the ventilation notches in my inner covers. The bees are nearing full spring build up mode so they have a lot of brood to warm, it was cold last night, and here's what I see when looking up there. This is why you want that air to have a way out. Imagine this all over the inner cover and dripping back down.