When purchasing an older house with a wood-burning fireplace, it's a good idea to have it thoroughly inspected. If the inside of a fireplace chimney is deteriorating, there is a danger of poisonous gases coming into the house.
There are certain specifications about height of a chimney and other dimensions and also about the shape and slant.
A word of advice about chimneys. When we had a wood-burning fireplace, I don't know how many times I started the fire without opening the damper (the door in the chimney that has to be opened before a fire is started.) If you forget, the smoke comes out and fills the room!