We took out a leaking commercial boiler that had a condensate tank and replaced it with 3 smaller semi-commercial boilers. We did this to provide a way to have multiple firing rates based upon system pressure. Also the benefit of redundancy exists this way. Someday a boiler will stop working but they will still have heat from the other two. For an apartment building that makes much more sense than one large boiler. Somewhere down the life of the building the wet returns were made dry. We removed all the F&T traps and restored the wet returns by using a false water line and adding air vents to the system. The three semi commercial boilers didn't have the water in the operating range that the original commercial boiler did so we installed a reservoir tank to provide the amount of water needed for steaming. This is a passive tank in that there are no pumps, controllers etc. that go with it. It works purely by the physics of the system. We wanted the feeder to be capable of being called upon by any of the three boilers so a relay system was employed to make this operate.