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Discuss Help! Nest - Dual zone - Opentherm! in the Central Heating Forum area at

  1. 1animal1

    1animal1 Member

    Afternoon all

    After getting to a point where i am almost ready for my new boiler system to be fitted. I am going for either a Viessmann or unvented but i think swaying towards the unvented due to hot water contingency if the boiler goes down (too many stories of people waiting days for parts, taking cold showers!). I have rigged the system to be easily converted to two zones for CH, S plan (currently one loop, S plan), obvious hot water and possibly a single water underfloor being added eventually.

    My original intention was to go with NEST gen 3 x2, one for each zone and the lower zone controlling the hot water. This is a medium sized 4 bed detached property, so nothing worryingly huge.

    Yesterday i took the time to contact a really helpful chap enquiring about Evo Home which I can see is a far superior system, especially when linked to Opentherm! My problem is the usual cost associated given that I have 11 rads, 2 of which (designer) have nice shiny new valves which won't be Evo compatible and are quite prominent (kitchen/Hall).

    This got me thinking about the benefits of Opentherm and upon reading, it sounds daft to ignore it. My problem is this though - from what i understand you cannot have duel NESTS on Opentherm as it understandably can only be controlled from one source, so is my only solution to stay with one ring? Maintaining what is in place now... if i want to use Opentherm..

    Possibly going to a single ring on Honeywell connect, using Opentherm bridge, hot water bridge - meaning i'll be opentherm from day one and able to add the TRV therms once i am able to afford (might need a second job just to pay for 11 of those :/)
    Last edited: Sep 12, 2017
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Are you going to be using all the rooms in a day (ish)

    If you are I would go with a stnd system eg trv and you can go for an internet controlled room stat

    Easier in the long run and less to go wrong etc

  3. 1animal1

    1animal1 Member

    Not really - it's only me and my wife living there so only 2 or 3 bedrooms are in use sporadically. We do intend on having children so that may well change in the near future which is what i was planning for..

    I had gone two zone as wanted the flexibility and to be efficient.. I can go either way given how it is currently piped. Currently the boiler in the kitchen pumps upstairs and drops into the downstairs halfway along the pipework which takes a while for the lower rads to warm up...

    I love the idea of Honeywell & Opentherm and the individual TRV's - the chap i spoke to really sold it to me! The controller looks pretty decent - but as you suggest, is the house big enough to warrant given that a single upstairs/downstairs stat will cover each room easily.

    What started me looking was when i have been looking for gen3 deals for 2 NEST's - cheapest i got it down to was £370 which isn't far off the Honeywell minus the TRV's (I can get the Honeywell cheaper if I can put up with the ugly remote stat for upstairs) - but then dual zone won't work if i go for the TRV's eventually...

    What do you do for large houses beyond 150sqm using Opentherm - fit 2 boilers?
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Problem with evo home you have to go fully in buy the lot as if you install zone valves in to separate up and down these will need the be removed once you buy the heads

    It's one of them big commitments
  5. 1animal1

    1animal1 Member

  6. Chuck

    Chuck Active Member

    Evohome, etc. are great fun, but if you're buying in the hope that fuel savings are going to cover its cost you may be disappointed.

    From the point of view of total cost of ownership, a well-balanced system with traditional TRVs and a programmer-thermostat is hard to beat.
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  7. 1animal1

    1animal1 Member

    The original idea was a dual zone to be more efficient than we are now - the only extra cost being an additional NEST and Diverter valve. My thinking now is that IF the Honeywell is light years ahead, coupled with Opentherm, then maybe i ought to consider. (although it isn't looking that way the more i read)

    Downsides is obviously the B Ache of changing 22 or 33? TRV batteries annually, changing nice new chrome trv's to the relatively ugly Honeywell versions (only 2 to do but will make the new rads look less designy - yes i just made that word up :) )and making my system Honeywell only - not exactly long term future proofing.

    If I wanted to save money I wouldn't be touching this lot at all - preferring to stay with my 66/100 rated 1986 boiler which is faultless and has about 3 things that can go wrong with it :)
    Last edited: Sep 13, 2017
  8. Matchless.plumb

    Matchless.plumb Trusted Plumber GSR

    Just on traditional Thermostatic trv's you will safe up to 5% but then again the rest of the system has to match and has to work efficiently to safe more on fuel. ( there many factors which are important to safe money in the end.)
    • Like Like x 1
  9. 1animal1

    1animal1 Member

    It seems to me that if i go Opentherm, with NEST I am limited to one zone and TRV's - Honeywell expands me to multiple zones where ever there is a rad.

    If staying away from Opentherm, the obvious choice is the dual zone NEST. I think it's either this or the full blown Honeywell - otherwise I can't see how heating one circuit through Opentherm is going to benefit over heating one floor on a normal cycle as per the NEST dual

    If I went Opentherm on NEST.. would that not be a similar system to the Honeywell - doing away with diverter valves assuming i have a single S plan circuit?

    Also, what do you chaps do for a house above 150sqm which requires more than one zone? Stay away from Opentherm or fit 2 boilers? o_O
    Last edited: Sep 13, 2017
  10. robj20

    robj20 Member

    Two zone nest will work with opentherm, its the bridge bit thats opentherm. Both nests will communicate via this.

    I have Evohome on 7 radiators with opentherm and it works brilliantly. When it first comes on the flow maxes out at around 80c, then as the zones heat up it takes the flow right down to 35 or so.

    What boiler are you getting or have? You know they dont all support opentherm.

    Your not only making your system Honeywell either, there are a few that do the whole each radiator is a zone systems, deltadoor and tado being two i looked at.
  11. 1animal1

    1animal1 Member

    Thanks Rob - what about the conflict of two NESTS requesting different temps for each circuit? One boiler, one continuous temp no?

    Not sure on the boiler yet - i will let my plumber gauge a few options towards the end of the year. When I'm ready for it to be fitted.

    So am I right in saying, with the Honeywell piping, I'd have to make my house a single ring? and how does the pipework look near the boiler - presume one diverter valve to the cylinder and open pipework on the rest? This is the bit that's confusing me about the Honeywell..
  12. robj20

    robj20 Member

    Mine is piped extactly the same just missing any zone valves. Still a flow and return in 22mm and 15mm to each radiator.
    If i ever wanted to change i would just need to fit zone valves where the 22mm splits off to upstairs.

    When you think about your setup with two nests how is it any more difficult that mine with 7 zones each can be requesting different temperatures.
    Im guessing it just averages it out and runs a flow that meets all demand then when all rooms are at temperature it reduces the flow temp.
    For instance if i have it on in the bedroom and the flow is 35c and then turn another radiator on the flow increases to bring the new zone up to temperature quickly. To compensate in the room that was already at the correct temp the radiator valve will either close or partially close.

    I hope that makes sense.
    By the way i love evohome, was worth every penny. So convenient and keeps each room exactly at the right temperature. Bathroom 22c, bedrooms 18c, livingroom and dining room 19.5c.
    • Like Like x 1
  13. 1animal1

    1animal1 Member

    That's fantastic insight, thanks Rob :)

    The dilemma now is purely cost related if i can put up with the TRV's on my nice new rads (only 2 need replacing, luckily only at one end). I would need for the Honeywell 11x TRV's, the controller, hot water module & Opentherm module (is there anything else I've missed?)- There's a few G3000's for sub £100 so I'd be talking £800 versus £355 for 2 NESTS...

    How often are you changing batts in the TRV's?

    So even though I've set up for 2 zones, the plumber could in effect connect these 22mm upstairs/downstairs pipes near the boiler for this particular set up? Currently the upstairs/downstairs are connected midway through the upstairs 22mm - i didn't know if i connect my new zones, if the water near the pump would go for the easiest option of downstairs..but i suppose the pressure would send it through both. Does that make sense?
  14. robj20

    robj20 Member

    You could use underfloor valves with actuators on instead of the radiator trv ones, use a bdr91 to control that actuator and fit a thermostat in the room.
    This is what im going to do when I add a designer bathroom radiator.

    You shouldn't need to remove any valves just have them manually set to both zones open.

    Not had to change the batteries yet, but when I do will be putting rechargeable ones in.
    • Like Like x 1
    Last edited: Sep 13, 2017
  15. 1animal1

    1animal1 Member

    So add another £150 to the bill rob? ;)

    That's out I'm afraid for one of the designers, for now - After piping downstairs at the weekend, I've now laid 6 boxes of laminate and I'm not taking it up :D (for another 2 years at least until i replace with the final flooring for downstairs hall/kitchen) That said it's not the end of the world to change a compression elbow on one end - and I'll get the tiny benefit of TRV shut off when the front door is open..:rolleyes:

    If this is a go, then it'll have to be a stealth purchase - she doesn't know the cost of NEST (which she'd go nuts at), let alone the Honeywell. :cool: :D

    What is the app like for day to day use? I had read that it had improved a lot - surely with any decent app, you'd expect geolocation to be around the corner, if it doesn't have it already...I've also read that Honeywell now have Alexa integration too. Moving at a rate of knots it seems
    Last edited: Sep 13, 2017
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