Tankless Project

[Brent]

I have a 82 unit hotel that is currently running 2- A.O. Smith Cyclone xi heaters ran in series and balanced with a recirc pump located in their boiler room. One of the heat exchangers died on the one of the cyclone heaters and it will not heat anymore. The owner bumped up the temperature on the working heater to compensate for the other heater that doesn't work anymore and is basically using it as a storage tank. The owner bought a navien np240a tankless water heater that has a built in recirculating pump. He wants us to mount the tankless unit in the electrical room that backs up to the boiler room. He wants the unit ran in series with the working cyclone heater, the non working heater is to be used as a storage tank. My question is about the recirc line. How would I plumb this to allow the the existing pump to be used as well as the pump built in to the tankless. The pump that is built in to the tankless isn't sufficient to pull the water across the hotel so the existing pump will have to be used.

 

[IFIXH20]

Leave the existing system as is and install the tankless to spec.

 

[buhrly]

The gpm through those units is not sufficient to run in series. It would need to be on a secondary loop and temperature controlled to the storage tank. It sounds under sized though. You should start with checking that it will take care of the demand.