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)?


2 Answers 2


Honeywell does not provide a ton of info, but from the installation manual it would appear that evoHome is assuming each room has its own feed and return pipe, and in addition has its own local valve. You're unlikely to find such a system in the USA -- and in fact I'm kind of amazed that UK homes commonly have such a layout. USA systems typically have one to 3 or 4 zones in the house, and all zone valves are near the boiler. A given zone will heat a few rooms with a single pipe loop, so you can't control on a by-room basis.

My impression is that this system is much more useful in a multi-office business space, as it allows centralized control of the existing valves in each office space.

  • As far as I can tell, the Evohome radiator valves install directly onto the radiator and can work in a single-zone system like a home. Alternatively, the Tado and the Netatmo appear to work the same way by replacing the knob or TRV on an individual radiator (I would have included the links in the initial post but was restricted).
    – mjbraun
    Dec 6, 2016 at 19:19
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    @mjbraun Depends on the UK definition of "zone" . There's no way a device attached to a radiator which runs in series with other radiators can control just that radiator. I bet the UK "zone" means there's one valve at the boiler which feeds all the radiator loops. Since each radiator has its own manual valve, and these loops are in parallel, here in the US we might well call them separate zones. Dec 6, 2016 at 19:43
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    @CarlWitthoft - You're correct that in the UK the typical setup is for all radiators connected in parallel, allowing each one to be controlled by a separate TRV. There isn't typically any "zoning". From a quick read of the Evohome page, it appears that replacing the TRVs with evohome radiator controllers and replacing the main thermostat with a main evohome controller effectively adds zoning without having to adjust any pipework.
    – AndyT
    Feb 15, 2017 at 10:08

Controlling the temperature of each radiator in a heating system is possible if the piping for the supply and return is piped as a direct return, reverse return, or monoflow system. I am not familiar with the type of control valves or system you mentioned above. The type of valve used will not matter as long as the heating system is piped as I have stated above. If you have cast iron radiators installed in your home then one of the piping systems I mentioned have been used. You mentioned thermostatic control valves, these would control the temp of each radiator that they are installed on. If you need more help I would call a large local HVAC contractor for help.

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