best architecture for boiler with thermostatic vales?

weil_fail

if you're designing a hot-water boiler system from the ground-up, what is the best way to design for condensing boiler? the return temp should be low, to stay condensing, right?

I've worked with the classic cast-iron radiators, but I would assume a low-temp system would require "hydronic panel" radiators made for low-temperature operation, right? are there any installation considerations regarding low temp radiators, regarding thermostatic valves, architecture, etc.? could one use the exiting piping and install low-temp radiators with thermostatic valves in place of the old radiators?

hot_rod

Any radiator can work at lower temperatures as long as it can meet the heat load. Ideally for condensing boilers a supply of 140F would typically return low enough temperature to allow condensing.

This journal guides you through determine how to run lower temperature in older systems designed for high SWT.

Starting from square one would be a room by room heat load calculation. Then select some radiator options and see what size and style you need to match each room load, BTU/hr.

Most all heat emitters have charts going down to 140F or lower.

https://www.caleffi.com/sites/default/files/file/idronics_25_na.pdf

weil_fail

if you're installing thermostatic valves, would you want to err on the high side with the radiator size, since it would have more ability to self-balance as each room comes up to temp? (obviously, the room with the heat-calling thermostat wouldn't get a thermostatic valve, and thus be more carefully sized.. or maybe slightly under-sized?)

pecmsg

In floor radiant heat just to keep the floors warm. Hot water coils in the A/C Heat Pump ducts for temperature control