my parents have an open fire in their house (so much better than gas, the smell, the heat and the fact you can burn stuff when you get really drunk!) and they've not had it cleaned in about 15 years, aparently the acid in the soot attacks the brickwork in the chimney and can cause more damage than good if you sweep it, although im not sure on this tbh!
chougs- get some nice seasoned logs (or some peet blocks if you can find them and get it used man!)