i want to change my gas fire to a wood burning stove and i want to be able to do all or most of it myself its the rule and regs im concerned with every thing i've read about a flue liner as the chimney was built in 1936 and would of burnt wood back then. it is a standard opening of 600mm wide by 590 high 400mm deep and the flue opening is 370mm wide 250 deep can anyone advise me please.