DCM1 service 1 of 2 Heat completed changed (1) 16x25x1 filter, tested system operation’s, did safety inspection on heat exchanger found unit has cracked heat Exchanger in middle cell under high limit. Unit has the potential to leak carbon monoxide into home, current readings are 0 PPMS. Heat exchanger are under warranty for 20 year. Please send over estimate. Homeowner is going to call to update name in system.