Controlling electric underfloor heating with a dedicated Evohome WiFi Controller

[FullBore]

I have four small rooms with electric underfloor heating (“EUH”)

Two, the kitchen, and a dressing room have no other form of heating.
Two a small bathroom & my study have “wet” radiators which are already controlled by HR92s, the UFH in these rooms is switched off during the winter.

Each of the EUH systems are controlled by Heatmiser PRT-E’s and each is well under 3.0 k.W. they are all connected through RCD protected switched fused spurs.

I am delighted with my Evohome system, which will be extended this summer to take up all available 12 zones on its controller.

During the summer the central heating will be switched off, but I would like to be able to use the EUH and control it in a similar manner to the existing EvoHome system.

It has been suggested that this could easily be done by installing a second Evohome controller, dedicated to the UFH with additional Honeywell kit.

Is this reasonably easy to accomplish, and what kit would I need in addition to the second controller, presumably a DT92E in each of the 4 zones + ??

Simple answers please as I am climbing a very steep learning curve.

[FullBore]

Bump - anyone please?

FB

[Fireblade69]

I think the only issue with using the Honeywell systems to control underfloor heating is that in general underfloor heating systems use a temperature probe embedded in the floor area rather than an air sensor on the wall. The Honeywell DT92E thermostat is wireless and cannot be hardwired to a sensor probe so would measure the air temperature to control the heat source - if this was particularly cold or did not correlate to the temperature of the floor very well then you could well overdrive the UFH (it could be constantly on) or you would have the DT92E set to some weird trigger point which would be odd but livewithable.

However, there's no reason why you can't use a BDR91 & DT92E (or Y87RF) pair to control the power to the heat mat if the load is lower than *5Amps, you can then eliminate the PRT-Es or you can add the BDR91 in series with the PRT-E.

I would certainly recommend you seek out a more professional opinion than mine though, perhaps using the above as a grounding for that conversation.

*BDR switchable limit - you can get more if you use a higher rated external relay which is then controlled by the BDR91's relay.

[SensibleHeatUK]

Controlling EUFH (or any electric heating)via Evo is no different to controlling wet heating with a couple of added steps.
With EUFH the existing floor sensor and stat has to be wired in series with the Evo actuator controller (BDR91 or zone from a HCC80R dedicated to electric heating) provided you use a suitable contactor rated for the load on the circuit rather than trying to switch the load directly. The floor sensor/stat are needed to protect the floor and heating element from overheating and causing damage. When the floor temperature is reached the heating will shut off regardless of the air temperature. This does not stop the room from heating though as it simply means the floor remains at approx 28 degrees until the air temperature setpoint is satisfied.
It is preferable to use a dedicated Evo Touch or Single Zone Stats to keep electric zones separate from wet zones so they do not operate the boiler.
The manifold controller is useful when controlling several zones as it makes installation neater.
Using an Evo room sensor means control is by air temperature only but this works well. You can force the floor heating on by setting a very high setpoint for a short period before going back to comfort temperatures to ensure the floor is warm when you want it to be.

[roydonaldson]

It would be good if you could have a Zone that did not fire the boiler, ie. have a tick box that says, Do Not Call. You could then use underfloor and timed zones independently of the boiler.