Completed full heating maintenance on (2) Carrier RTUs and (3) Lennox unit heater. We checked mechanical and electrical components, checked flame sensor reading, inspected heat exchangers, changed filters and verified proper temperature rise. RTU 2 was condemned for heating on a previous maintenance due to a cracked heat exchanger. RTU 2 also has a failed gas valve that needs to be replaced. A quote has been sent to replace these components. RTU 1 is operating at factory specifications at this time. RTU 1 heat exchanger has lots of surface rust but no cracks at this time. A quote will also be sent to replace this heat exchanger as well as a preventative measure as these units are the same age. Information will also be sent to our office regarding replacement bids for both units. After inspection of the warehouse unit heaters we found UH 3 to have a flue pipe that was detached from the ceiling. The entire length of flue piping from the double wall stack to the inducer assembly was rep