Choosing an Indirect Water heater via MBTU/Hr rating

Dear Readers,
I'm trying to select an indirect water heater to retrofit my boiler from a tankless coil. The literature for indirect water heaters lists a Minimum Boiler Output (MBtu/hr.). Would this number be my boiler's "DOE Heating Capacity" or my boiler's "NET I-B-R Ratings-Water"? These are the only two ratings I can find for my boiler in MBtu/hr.
Any advise appreciated.
Anthony M. Falcone
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what are the numbers

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Phase III Indirect Water Heater Model #TR-45: "140,000 Boiler Output BTU/hr" I assume that means that this model needs a boiler with an output of 140,000 BTU/hr.
My boiler: "Buner Capacity: 147MBH, DOE Heating Capacity 129 MBH"
Not sure if this means my boiler can/can't handle this model of Indirect water heater.
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I would suggest that you hire a professional, before you end up spending a lot of money on something that doesn't work correctly.
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