On very warm or humid days I see a bunch of bees at the front of the hive fanning like crazy. On bad days the bees leave the hive and crawl all over the front. This is due to an increase in heat and humidity inside the hive.
If you see lots of bees on the front of the hive, pull out the mite board on the bottom to let more air into the hive. If you see the hive building up propolis at the hive entrance you can put the bottom board back. Bees need to be warm and have their own methods for keeping the hive at the right temperature. They are good at it, but you need to watch for signs that they are uncomfortable and help them if you can.
When I added the last supers I put a one cent piece at the corners of the bottom deep and this made a slight gap between the bottom and the first super. The bees can use this to gap to control the ventilation in the hive. If it is too cold they will close the gap. A penny is thin and the bees can easily close the gap. If the hive is too warm they can open the hole up again. A penny is as cheap as you can get for a useful tool and is thinner than a wooden matchstick, which is usually recommended.
If you are in a hotter climate you might make similar gaps between all the supers.
Take the pennies out in the fall. The bees will regulate the temperature naturally by fanning when they need to, and they will need to conserve their heat when the temperature starts to fall.
