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Thread: Evohome and floor probe for wet UFH under vinyl

  1. #1
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    Question Evohome and floor probe for wet UFH under vinyl

    Hi

    I'm looking at installing Evohome as part of a large house renovation. I'd like to control some wet underfloor heating in a slab, where the flooring is going to be amtico or some other vinyl. These tiles can only be heated up to 27 degrees but it seems Evohome doesn't have a native facility for adding a floor temperature probe.

    I've seen it suggested that you can put a second floorprobe specific thermostat "in series" with the evohome thermostat, but I don't really know what that means. This Honeywell FAQ document also suggests it is possible. https://ensupport.getconnected.honey...rfloor-heating.

    1) Has anyone any experience of using a floor temp probe with Evohome? The UFH, boiler and thermostats will all be bought new, so if there's a system that works then I could probably get it.

    2) Has anyone got Evohome running with UFH and vinyl without using a floor probe? It has been suggested that you just need to set the flow temperature in the UFH to a low enough temperature so that the floor never gets that hot. That makes me nervous given the cost of replacing the floor if you accidentally "cook" it.

    The Evohome system will also be controlling a load of radiator zones via TRVs, and the hot water.

    Any assistance gratefully received.

    Peter

  2. #2
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    Peter,

    I don't have wet underfloor system but I have researched it as it is something I would like to implement. I didn't think that they needed an underfloor temperature probe. Electric UFH does as without one it will the temperature of the mat will continue to increase until it reaches the room set point, or the insulation of the cabling in the mat breaks down, whichever occurs first. With a wet system, you set the maximum flow temperature with the mixer valve at installation and it never goes above this.

    Guyan

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    Hi Guyan

    I'm beginning to think you are correct.

    The thing I don't understand is what temperature you would need to set the mixer valve at. Presumably a 30 degree temp at the valve (for example) wouldn't lead to a 30 temperature of the floor covering, due to heat losses etc. And wouldn't it be subject to ambient temperature changes, i.e wouldn't you get a hotter floor in the summer than in the winter.

    Ultimately, I suppose it depends on how much heat you need to heat the room. If you can set the mixer to a low enough value that the floor never gets close to 27 degrees in any season, then you would be fine. If you need more heat because the room is cold, then that would be more of a problem, but then I suppose that's a problem even if you have a floor probe...

    Peter

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    So I went to the Grand Designs show at the NEC yesterday and asked various UFH suppliers about this.

    Most (not all) were a bit scared of running a wet UFH system under vinyl without a probe. Not that you couldn't set up the system so it shouldn't ever get too hot, but "what if the design parameters changed". I.e. either freak weather, someone messing with the setting on the manifold or something. This may demonstrate a lack of confidence in their own ability to design the system properly.

    They also said amtico and others wouldn't honour the guarantee on the floor without a probe... although I understand its very hard to get Amtico to stand behind their guarantee anyway...

    Pete

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    Hi Peter,

    All the temperature safety aspects of water ufh are done in the ufh circuit, and are nothing to do with the smart controls that are setting room temp and schedule. Either you have a safety cut out thermostat on the output manifold ( as in our system) or you have a safety cut out thermostat connected to the floor . These safety thermostats shut down the mixing pump and/or inlet valves to prevent hot water entering the ufh system.
    Basically look at ufh system as providing water at a fixed temperature . This is achieved by setting its flows and valves to get the optimum pipe temperatures without overheating the floor. - usually this equates to manifold temp of 35-45deg but these temps and the initial set up takes a while to set up correctly .

    Once set up the ufh system should not need adjusting again. The smart controller such as evohome is simply used to operate the manifold valves to open and close based on room temp , target temp and schedule. In our system this is done with Evohome with a hcc80 ufh controller .

  6. #6
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    Hi there rvb99

    Thanks for posting. The safety cut off thermostat that you are using, is that measuring the temperature of the water in the water output and then just turns off the water if it is hotter than it should be?

    You also mention a safety cut off that could be connected to a floor probe though. Do you possibly have a link to such a thing?

    Thanks again

    Pete

  7. #7
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    These thermostats only trigger in exceptional circumstances and have to be manually reset . In our system the safety cut off thermostat is mounted on the side of the output manifold . if the temp ever goes above 50deg ( which corresponds to a floor tile temp of approx 28-30deg the system will shut down .

    Similar thermostats exist where the probe could be mounted into the floor Eg if I wanted a cut off based on floor temp I could use one of these and insert the probe into some conduit that goes into the floor .

    https://www.heatingcontrolsonline.co...tat-p-786.html

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    Thanks for the link.

    Forgive the basic questions, but I'm new to UFH and thermostats in general. Is there anything specific I need to look for to ensure the pump or valve in the UFH is able to be wired up/controlled by an external thermostat? And is there anything special with those particularly types of capillary thermostats you mentioned. Someone else pointed me towards these https://www.underfloorheating-uk.co....ng-thermostats. Could you use one of those instead of the one you linked to?

    Finally - if the safety cut out thermostat shuts off the valve or pump, doesn't this clash with Evohome which may be thinking that the pump is on and water is flowing. How does Evohome cope with this, or does it just not know?

    Thanks

    Pete

  9. #9
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    When the ufh is operating the aim is to keep the manifold temperature and water parameters constant. The temperature set up in the system is such that under normal operating the floor will never go above say 25-26 deg ( or whatever you choose)

    You are not controlling water temperature. Just the time the water is flowing via evohome.

    The safety cut outs are exactly that . They operate separately from the main controller system and are designed to protect the floor in case of a failure , for example mixing pump failure. Evohome will know nothing about the cutoff, unless you wire the hcc80 such that it , along with the pump, also shuts down should the cut off kick in . In this case the controller will show loss of communication with the hcc80

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