UFH + rads + Nest + OpenTherm

20 Mar 2012
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United Kingdom
so I want to add UFH to my existing single-zone single-nest heating system, the nest is wired to my Combi via OpenTherm.

I want to keep the OpenTherm if possible as it helps the boiler modulate for peak efficiency.

It is not possible to chain nests together unless you use the dumb On/Off control method, so I’d have to sacrifice OpenTherm.

Can anyone think of any nice innovative solutions that will get me what I want?

I was thinking dual-zone with one zone controlling a zone valve and one wired direct to boiler, but that would only allow On/Off for the zone, and would only work when the master Nest was on.

I also thought about having smart TRVs on all my rads, and making some kind of software-based controller (on my raspberry pi) to control them based on either a schedule or another nest. The nest would then mostly just control my UFH
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The Honeywell T6 Lyric is capable of two-zone OpenTherm, and provides the same functionality as Nest with an upgraded version of the OpenTherm protocol
If only I’d asked this question before buying the nest...

I’d then have found the evohome too which also does something like that and gives me indepentent control of each room.
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