My mom lives in a 50 year old apartment building with radiators, and all winter long the windows are open because it is so hot. When Graham Hill was planning his LifeEdited apartment project, we talked about the problem of radiators, and how the only solution for control was to get the landlord to install expensive thermostatic valves.
It's a big issue; poorly controlled steam and hot water radiator systems are in 14 million housing units in the United States, and in Canada too, where I have a three storey house and cannot balance the rads no matter how I try.
NYSERDA estimates that the typical amount of heat wasted by overheating of steam buildings is between 15-30%. In terms of energy, this waste, for residential structures in the US alone, cumulates to approximately 86 trillion BTUs annually. The emissions from this kind of energy waste equate to approximately 6.3 million tons of CO2, or 1.25 million cars on the road. Financially, the implications are enormous, and depend of local fuel prices. In Manhattan alone the waste due to steam heat inefficiencies cost about $700 million a year.
That's why Radiator Labs' idea is so stunningly simple and clever. They stick an insulated box over the radiator and have a thermostatically controlled fan turn on or off as heat is required. Every radiator becomes an individually controlled zone. Heat that isn't radiated into the apartment stays in the system instead of being let out the window.
According to Fast Company, "The on/off data from all the apartments in a building is sent to a central node (perhaps in the boiler room), to influence how the heat is generated. " This is nice, but could be a problem if tenants are putting these into rentals and the landlord is uninterested. However I don't think it is absolutely necessary; a furnace turns on in response to demand, and if the rads aren't pumping out heat then the demand is reduced. Wherever the thermostat is will get hotter faster and turn off sooner.