All posts regarding the care and breeding of catfishes from other parts of the world (North America, Europe and Australia). If you don't know where your catfish is from, post a query in the identification category.
Don't even worry about heating the tank, room temperature is fine for native fish. Ideally you would also need to get it a bigger tank, that's not very big for a fish that can grow a lot larger than 5".
Seeing as how you have only one post, I'm not sure if you have experience with fish at all. Assuming you do not, you'll also need a filter of appropriate size for your tank, dechlorinator to treat tap water for putting into the fish tank, and some sort of fish food, such as sinking shrimp pellets.
- Milton Tan Biology Grad Student @ Auburn University
In many states it is illegal to transport and keep live game fish.
However the OP is from Pennsylvania and as long as the fish is legally caught they have no such restrictions. There is also not a minimum size for catfish in Pennsylvania so the fish is perfectly fine to keep in an aquarium.
But a 20 gallon long is much too small of a tank for a Bullhead and it will need a larger tank (around 75 gallons at a minimum) eventually.