It takes more than just having a bat house to attract bats into your yard. You must place it in the right spot, and you must paint it the right color. Bats are not color sensitive, but they are very sensitive to temperature. The color will help you control how much heat your bat house will absorb or reflect depending on where you live.
Dark colors absorb heat while light colors reflect it.
Once you have figured out how to maintain the best temperature, you need to find the best spot. Bats prefer an unobstructed area so that other animals like squirrels and raccoons do not bother them. Bats are migratory and should begin arriving around early summer. Experiments show that if you put your house up in the fall or winter, it will more likely be occupied. Bats usually stay around till fall.