It's a perfect combination of high mass radiators, and a modern condensing boiler. However, the cheaper look-a likes from the big box store may only be water-heaters, which will not work as boilers.--NBC
Some of the boilers I am looking at rated by input. How will I now what the output is. Right now I have a gas conversion burner that set up with 100,000 input would the condensing burner be about the same.
The only way to correctly size a boiler is to do a heat loss calc.
The output is the input derated by efficiency.
A 100,000 BTU boiler that is 90% efficient would have an output of 90,000 BTU at sea level.
Lochinvar,Triangle tube and Viesmann are some good choices.