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Thread: Evohome and UFH - am I on the right track?

  1. #1
    Automated Home Jr Member
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    Aug 2018
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    Default Evohome and UFH - am I on the right track?

    Hi all

    I only discovered this site a few days ago and within that short time have learnt more about Evohome than Iíve gleaned from months of random reading so, as a lurker, Iíd like to thank you all for your fantastic contributions. Having said that, please excuse what will appear my simplistic question.

    Briefly, my situation is a 3 storey + cellars Victorian end terrace ie lots of stairs! Current gas usage typically 23K KwH on a WB Greenstar combi. That figure also includes gas range cooker. There are 14 rads all fitted with Drayton TRV4s. System is controlled wirelessly with a Drayton digistat programmable thermostat and a lot of legwork/twiddling.

    Only complicating factor is a kitchen/ dining room which has wet UFH. When installed this was teed off the rad circuit (!) so currently is not independently controlled. The manifold obviously mixes the radiator water temperature down but as things stand itís only on when the programmer is calling for heat and other radiators are on. The UFH wall stat will switch its circuit pump off and on as required but things are obviously not ideal. As a first step Iím having the floorís flow & return routed directly back to the boiler shortly with an appropriate zone valve. S-plan seems to be the way to go.

    I realise that any smart system will not inherently save any cash but it should make things a little more comfortable and way more convenient. Iím also looking for more stable temperature control within any room when itís being heated. Iíve looked at Wiser, Tado and Evohome but rejected the first two for all of the well documented reasons. As a bonus my place naturally divides up into 12 zones so Honeywell it is. My only question relates to controlling the underfloor heating which effectively is a single zone. The Evohome UFH controller will handle 5 zones I think and is rather expensive and overkill for my needs.

    Iím prepared to shell out the cash for the base pack and HR92s and wonder if I can use the Evo controller to handle all of the radiators while still using the digistat to program heating times for the floor. I canít understand whether the boiler will be able to receive commands from two independent controllers. I appreciate that Evohome talks to a BDR91 boiler relay and wonder whether itís possible to have 2 relays in parallel which can instruct the boiler separately?

    Sorry for the long winded question! I know this has scenario has been touched on before
    In several threads such as https://www.automatedhome.co.uk/vbul...e-UFH-question but I wanted to be confident I was on the right lines before I commit to the Evohome kit.

    Iíd be really grateful for any help and please excuse my ignorance around basic plumbing layouts and this area of technology in general.

    Jim

  2. #2
    Automated Home Legend
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    Jul 2014
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    Default

    If the UFH heating manifold is just a single zone then dont bother with the Evohome UFH controller, you dont need that. Just a single Y87RF will do. You will use the BDR91 included in that to open the zone valve, which in turn will start the pump and fire the boiler. Simple. The UFH controller is only needed when you want to zone partition a single manifold.

  3. #3
    Automated Home Jr Member
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    Aug 2018
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    Thank you so much Bruce for your very clear help. It is indeed a single zone so no UFH controller is required - great!
    Two further question if I may: does that mean the Evohome controller can be bound to the Y87RF to provide scheduling? Also can a DT92 be substituted as it would fit a hole left in the wall by an existing stat?

    Thanks again

    Jim

  4. #4
    Automated Home Legend
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    Yes you can use either the Y87RF or the DT92 as the temp sensor. Once it is bound to the Evohome, the Evohome handles all the scheduling.

  5. #5
    Automated Home Jr Member
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    Thank you so much Bruce and for being patient with me. You've helped me a great deal.

    Jim

  6. #6
    Automated Home Lurker
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    Sep 2018
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    A quick question: I see from the answer above that for a single UFH system, the rather expensive HCC80R Underfloor Heating Zoning Controller can be replaced with a Y87RF single zone thermostat, as long as the UFH system has its own zone control valve. I have two separate wet UFH zones + 2 rad zones. Is it also possible to connect the two UFH zones with two Y87RF single zone thermostats, one for each zone valve? I

  7. #7
    Automated Home Legend
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    The HCC80R is only needed if you need to divide a manifold into multiple zones. If the single manifold is serving a single zone then you don't need it. So in your case if your two UFH zones each have their own manifolds and zone valves then yes, you can use a Y87RF in each zone to control the zone valve, which in turn will control the UFH pump on the manifold.

  8. #8
    Automated Home Guru
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    Dec 2016
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    I don't think above tips will work for every type of UFH - probably just the old ones.

    In my house the UFH is a computerized mix and pump system that responds to whether hot(ter) water is offered to the system. Unlike with old systems the pump is not constantly running, but the computer will crank the pump once in a while even if the heating is turned off - to prevent the pump from getting stuck.

    Obviously I can still switch that off by pulling the plug, or use a BDR91 to control power, but that will defeat the system's health mechanism. Instead I think the best way is to install an additional valve controlled by an HR92. Thoughts?

  9. #9
    Automated Home Lurker
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    Many thanks for the helpful response, I will go for the simpler Y87RF set up.

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