For those who have bats in your chimney and not in any other portion of the home or attic, the situation is a bit easier, since the bats are restricted to a small area. Before I discuss bat elimination tactics, there are two essential things to bear in mind!
Make certain THE DAMPER IS SHUT - So that bats do not get in the house and begin flying around as soon as you do your bat exception.
DO NOT START A FIRE - you'll need to open the damper to begin a fire, and if you do, bats will get in the house. Additionally, bats can fit through very little places, and you might find bats in the attic and walls should you start a fire.
Fortunately, finding the exit point is simple - it's the large hole on top of the chimney! Lots of the instances of bats in chimneys that I see are really the result of bats going in through openings where the chimney meets roof, or in decayed and open places. Bats do not always like to go through a large, vertical hole. They like small horizontal openings best. Therefore it pays to do a complete bat inspection to discover just where they're going in and out. A night watch helps a whole lot. Even in the event that you know you have bats crawling about and making noises from the chimney flu, you may observe that the bats flying out of areas you did not expect.
If they're coming from the surface of the flu, you want to pay special heed to leaving a gap over the exclusion netting, so they can fly up, then out and around the bottom of the exclusion netting. It's pretty tough to set up correctly. I honestly suggest hiring a professional bat removal firm if you have got a colony living in your chimney.
Oh, and one other thing - of course, if you have a colony of bats in the chimney, it is a maternity colony of females. They give birth to their pups in May, and the young bat pups can't fly until mid-August (timing varies a bit by species and part of their country) so PLEASE don't remove bats from the chimney during those summer months, referred to as the pregnancy season. If you do an exception during the summer, the infant bats will be stuck indoors, and I have seen a lot of problems with baby bats in the summer, it is crazy. Without their mom, they crawl all over the place, and get in the home.