By Connor Long - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=43154585
What Kind of Bat Is It?
Both the little brown and big brown bat can end up in the house in winter, but it is much more likely for the bat to be a big brown bat. Big brown bats, Eptesicus fuscus, have a body size of 3.9-5.1 inches and an 11-13 inch wingspan. They are more solitary than little brown bats and more likely to hibernate in an attic, crawl space, or wall.
If you have a "winter bat" it's probably a big brown bat. Bats awaken occasionally during winter to move around a bit, or to adjust to changing temperatures if their spot is suddenly too warm or cold. It is at this time that they can find their way out of the crawl space and into the house.
What Should I Do?
While wearing gloves, place a container over the perched bat and and scoop it into the container. If temperatures are above freezing, the bat can be released outside and should be able to find a new place to hibernate—under some bark, a hole in a tree, hopefully not back in the attic!
If temperatures are well below freezing, you can keep the bat in a box overnight until temperatures rise in the day, and release the bat at that time. Bats should not be kept contained like this for long as they will quickly dehydrate in warm temperatures in the house.
If a bat appears in the house during a prolonged deep freeze, you should contact a local wildlife rehabilitator who is licensed to care for rabies-vector species and see if they are able to take the bat.