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Thread: My evohome plan: does this make sense?

  1. #1

    Default My evohome plan: does this make sense?

    Hi,

    I'm very tempted to install evohome in our small split-level flat but I just want to make sure that what I'm planning actually makes sense

    Existing installation
    • A combi boiler
    • Five radiators, one per room, all with TRVs
    • One radiator in the downstairs hall with a manual valve
    • A combined wireless thermostat/timer in the downstairs hall
    • A towel rail with what looks like a TRV but the head isn't detachable


    What I want to do
    • Install evohome, obviously
    • Replace all the TRV heads with HR92s
    • Replace the wireless thermostat/timer with ... something? Nothing? Not sure


    My questions
    • Does this make sense and will it work?
    • How will the hall radiator and the towel rail work?
    • Is it possible to tell the evohome that there's a zone which will always heat up when the boiler is running?
    • Could I put a wall thermostat in the hall to control this zone?


    Many thanks in advance for help and suggestions!

  2. #2
    Automated Home Guru MichaelD's Avatar
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    Quote Originally Posted by Flup View Post
    Hi,

    I'm very tempted to install evohome in our small split-level flat but I just want to make sure that what I'm planning actually makes sense

    What I want to do
    • Install evohome, obviously
    • Replace all the TRV heads with HR92s
    • Replace the wireless thermostat/timer with ... something? Nothing? Not sure


    My questions
    • Does this make sense and will it work?
    • How will the hall radiator and the towel rail work?
    • Is it possible to tell the evohome that there's a zone which will always heat up when the boiler is running?
    • Could I put a wall thermostat in the hall to control this zone?


    Many thanks in advance for help and suggestions!
    It does seem to make sense.

    The evohome boiler relay, working with an evohome controller, will replace your thermostat & timer.

    The hall radiator and towel rail will come on when any of the radiators call for heat. If the HR92s are all in rooms that are at the right temperature, then the boiler will switch off, and the towel rail and hall rad will be off too.

    There isn't a way to tell Evohome about zones that it doesn't control, but it doesn't need to know, it can't do anything with them. It is actually considered good practice to have at least one rad or towel rail that is 'always on', so that the boiler doesn't damage the pump by trying to pump water round a system with all the rads shut off. Its often called 'always on', but of course, if the boiler is off, then these are off too.

    You could put an evohome thermostat in the hall, but it couldn't control the hall temperature, unless you put a HR92 on the hall rad, so would be mainly pointless.

  3. #3
    Automated Home Ninja Dan_Robinson's Avatar
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    Do not include the bathroom.
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

  4. #4
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    It does make sense, and is similar to what I have at home. My radiator without a TRV is in the bathroom. I have added a wall thermostat bound with a BD91 as its actuator (you must have an actuator, or the system throws up alarms). All that is connected to the BD91 is the mains supply, there is nothing connected to its relay terminals. The bathroom rad comes on if the bathroom gets too cold, or any other rad calls for heat.

    Regards,

    Alan.

  5. #5
    Automated Home Sr Member
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    I guess you could do something similar by nobbling the mechanics of a HR92 baseplate. Eg cut the pin on the black cog so that the HR92 can never close the bathroom radiator TRV. This way you have the sensor to call for heat and you have an actuator to satisfy the system but which in fact has no effect.

  6. #6
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    Each to their own, and I've said it elsewhere already but personally I much prefer to have all radiators including bathroom radiator under HR92 control, and see this as an Evohome benefit, if you take advantage of it. Of course this requires an automatic bypass valve to be in the system but you really should have one anyway for other reasons.

    Why do I want my bathroom controlled ? A few reasons...

    1) In warm weather or during summer the bathroom radiator is the only one in the house I want to use, in the case of drying towels and the room after a shower, keeping the room warm when bathing a baby etc. If it's uncontrolled then I have no choice but to turn on the radiator in another room so I can get heat in the bathroom - wasteful of gas, and if the weather is quite warm making that other room uncomfortably hot. Exactly the same problem I had with the old system in the house where I would have to turn up the hallway stat (and hence hallway radiator) so I could get the bathroom radiator running, making the hallway and nearby rooms uncomfortably hot.

    With individual control I can turn the bathroom up or down as I please at any time without affecting or bringing on any other zones.

    2) I don't want the bathroom hot all the time when the heating is on, but when a shower is expected I want it nice and hot. So in mornings I can schedule it to automatically be 22 degrees before shower time, but in the evening for coming home it's only scheduled for 18 degrees which is warm enough for a quick pit stop but not unduly hot and wasting gas.

    3) Having it under control also allows useful tricks - for example in the mornings as well as it coming on to 22, (and it usually gets turned up a bit further manually when the shower is used) every other zone in the house is scheduled to go to 5 degrees at 7:20am which is when we leave the house, however the bathroom is scheduled to stay on by itself until 8am. This allows plenty of time for towels and the room to dry before it goes off - this works brilliantly to keep the room dry and mould free without resorting to an uncontrolled radiator that is just hot all the time the heating is on.

    If the bathroom radiator was uncontrolled I couldn't do this, and the room would also sit damp during the day after we left for work until the heating came on in the evening, but then run for hours when it wasn't really needed. With it staying on until 8am it gets the room dry right away then goes off for the day then when it does come on in the evening it comes on at a much more moderate temperature suitable for quick visits instead of showers.

    4) Our upstairs bedrooms are not very well insulated so in the winter we have no choice but to schedule our sons bedroom on at a moderate temperature through the night - Evohome allows me to do this and have only his room running, and only as much as it needs to to maintain a comfortable temperature. If I had a bypass radiator in the bathroom or hallway those radiators would be running wasting heat and gas all night long... but with all radiators controlled the one radiator in the bedroom is the only one that runs at all in the night, yet the bathroom is still able to be scheduled to be piping hot for morning shower time. Anybody who needs to schedule their bedrooms on through the night really should think about eliminating all uncontrolled/bypass radiators, or you will be at least doubling your night time gas use...

    Just my person opinion but I think getting rid of always on/bypass radiators is one of the real benefits of a system like Evohome.
    Last edited by DBMandrake; 18th October 2017 at 09:24 AM.

  7. #7
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    Quote Originally Posted by DBMandrake View Post
    1) In warm weather or during summer the bathroom radiator is the only one in the house I want to use, in the case of drying towels and the room after a shower, keeping the room warm when bathing a baby etc. If it's uncontrolled then I have no choice but to turn on the radiator in another room so I can get heat in the bathroom - wasteful of gas, and if the weather is quite warm making that other room uncomfortably hot. Exactly the same problem I had with the old system in the house where I would have to turn up the hallway stat (and hence hallway radiator) so I could get the bathroom radiator running, making the hallway and nearby rooms uncomfortably hot.
    Or you could install a dual-fuel towel rail, which has an electric element in it for use during the summer months. For example:

    http://www.bestheating.com/info/blog...l-towel-rails/

  8. #8
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    Quote Originally Posted by Edinburgh2000 View Post
    Or you could install a dual-fuel towel rail, which has an electric element in it for use during the summer months. For example:

    http://www.bestheating.com/info/blog...l-towel-rails/
    Why would I want to go to the expense of installing something like that (including running power to the bathroom for the first time) when electricity is about 5x the cost of gas per kWh ?

    Also a towel rail is not exactly going to heat up and dry the entire room, just dry towels. I currently have an 800x600 Type 21 radiator so no electric towel rail is going to be able to replace that in winter for room warming ability, and there is no room for both a radiator and a dedicated towel rail.

    My hot water is S-Plan so the boiler is still coming on in the summer from time to time for hot water anyway.
    Last edited by DBMandrake; 18th October 2017 at 12:37 PM.

  9. #9
    Automated Home Sr Member
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    I'm going to control each room with evohome as well, seems daft to leave some radiators uncontrolled.

    Quote Originally Posted by rvb99 View Post
    I guess you could do something similar by nobbling the mechanics of a HR92 baseplate. Eg cut the pin on the black cog so that the HR92 can never close the bathroom radiator TRV. This way you have the sensor to call for heat and you have an actuator to satisfy the system but which in fact has no effect.
    Why would you do that rather than fit a thermostat to the room.

    Quote Originally Posted by rvb99 View Post
    I guess you could do something similar by nobbling the mechanics of a HR92 baseplate. Eg cut the pin on the black cog so that the HR92 can never close the bathroom radiator TRV. This way you have the sensor to call for heat and you have an actuator to satisfy the system but which in fact has no effect.
    Quote Originally Posted by Alan C View Post
    It does make sense, and is similar to what I have at home. My radiator without a TRV is in the bathroom. I have added a wall thermostat bound with a BD91 as its actuator (you must have an actuator, or the system throws up alarms). All that is connected to the BD91 is the mains supply, there is nothing connected to its relay terminals. The bathroom rad comes on if the bathroom gets too cold, or any other rad calls for heat.

    Regards,

    Alan.
    With that setup though you could overheat the room. HR92 or 91 on all rads, job done.
    Last edited by robj20; 18th October 2017 at 12:57 PM.

  10. #10
    Automated Home Ninja Dan_Robinson's Avatar
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    You just said the towel rail won't heat the room, then it will... 🤔

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