X10 technology can permit to close/open an electrical circuit. These systems can be managed with free software under Linux as
heyu.
You can get temperatures with captors on one-wire buses. These captors can be accessed with free software under Linux as
owfs.
You can program any radiator, by switching them on/off with X10.
At home my radiators are divided into 2 zones, the 1st is the living room/kitchen with 3 radiators, and the 2nd is the rooms and bathroom with 4 radiators. Each radiator has its own thermostat, but they are managed by a programmer to tell them if they must keep "comfort", "eco" or "no freeze" temperature, or stay off. On the radiator you set the "comfort" temp, the "eco" temp is at "comfort" temp minus 2-3°C (depending on radiator design).
The signal is sent on a dedicated wire, 1 wire per zone. When there is no voltage then the radiator is on "comfort". When there is a not null continuous voltage then the radiator is on "eco". The "no freeze" (7°C, depending on radiator design) is an squared signal with a precise frequency.
With such programmable radiators, you can send them "comfort"/"eco" commands with X10. I don't think you can send a "no freeze" signal with X10. Some free software permit to program X10 from Linux, eventually by also using one wire data, such as
misterhouse.
Have fun,
Denis.