I have a single-zone hot water radiator system and I was looking to balance out differences in room temperatures without going so far as to install another zone at the boiler. While there are thermostatic radiator valves I could install to give a bit of control over individual radiators, I was looking at a more "intelligent" solution like the Honeywell Evohome, a Netatmo Valve, a Micropelt or a Tado. But none of the products seem to be available in the US, which suggests that there is a fundamental difference between US and EU hot water radiator systems, though I cannot find anything concrete.
Is there a difference between radiator systems other than connectors? Or could I theoretically import and install the devices (assuming no FCC issues)?