First, I want to check if there are any red flags about installing a condensing modulating boiler w/ indirect hot water in an old home with cast iron radiators in Minneapolis. I need to add an additional zone for a previously unconditioned space with plumbing. There I am planning to add a single wall hung radiant panel. My understanding is the cast iron radiators typically operate with water temps at 180 degrees F, the wall hung radiant panel at 150 degrees F, and the hot water will be heated just above 120 degrees F. Is it a problem for a single modulating unit to supply different zones with different temperature demands? Would there be different temperature demands?

Second, is it important to select a modulating unit with a low MBH output so that in the summer when the unit is only supplying hot water it is not using more energy than a well insulated gas fired water heater with its own burner (40 MBH output typical)? If yes, how low?
I live in a frugal household – 2-3 people, 1 shower, 3 sinks, washer, no dishwasher use.

Lastly any experience among the brands of condensing modulating boilers and indirect hot water tanks? So many brands on the internet, I imagine there must be some quality differences in the hardware. Also anyone know of an indirect hot water tank insulated with more than 2” of foam?

(Any recommendations on a free web based heat loss calculator?)

Thanks,