Get the chimney swept and have it smoke tested where they light a smoke 'bomb' in the fire place and check the upstairs rooms and loft for leakage as well as the out side.
Check to see if you are in a smoke control zone before using logs or smokey coal. The trouble with burning just logs is getting the temperature right as you can produce tar and other oils which stick to the chimney sides and have a habit of combustion after years of build up
Isn't this why you should have your chimney swept regularly?