I need to replace my old AO Smith copper tube 128K boiler that heats a gravity conversion cast iron radiator system and am in between whether I should go with a new cast iron boiler (like a Burnham 2 series) or a modulating condensing boiler (Nortitz NRC or NTI TNT).
I noticed that my current boiler has somewhat of a big temperature differential. The boiler temp is 130 and the water was 110 after the air separator (a big old Purgetrol) and returns at 96. I am concerned about the condensation risk going forward and I want to eliminate it.
If I go with a non-condensing cast iron boiler, I am concerned about condensation, but that risk can be mitigated with a primary/secondary loop with a mixing valve and maybe running the boiler at a higher temperature than 130 (I wonder if there is a reason it is set at 130 and not higher). The main benefits would be longevity (20-30+ years) and less maintenance. And I can keep venting through the chimney, which I am getting inspected to make sure it is fine and doesn't have any condensation damage. This is probably a cheaper option.
If I go with a modulating boiler, I eliminate condensation risk, I can get some space back. I would probably save money on gas, but the average life is shorter (12-15 years). I would vent outside and drain the condensate to the sump pump. There is more maintenance. This is probably a more expensive upfront investment, especially if I need to also replace the hot water heater with an indirect tank.
The system is a single line consisting of 10 hot water cast iron radiators. I would love to get your opinions on the performance of modulating condensation boilers on a converted gravity system or if it makes sense to go with a traditional cast iron boiler.
Thank you in advance for your help!
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