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I've seen per radiator t-stats for steam radiators on Ask TOH. Is there something similar for forced hot water radiators?
Yes here's one example http://www.bellgossett.com/homeowners/BG-ElectricZoneValves.asp
JLMD is correct.
There are also TRV's (thermostatic radiator valves).
What application did you have in mind?
Is there some problem you're having with a particular radiator or room?