Diagnosed furnace short cycling due to exhaust being pulled back in thru intake. Flue pipe ended approximately 2" short of flue termination cap causing flue gases to be expelled into wall and also allowing it to be pulled back in thru intake. Extended length of flue pipe to allow proper termination Customers system is 19 years old and has rust spots forming on heat exchanger Chambers. Customer would like an estimate to replace the system due to age, condition and recurring issues in the short time since they've owned the home