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Thread: Minimum Temperature - sledom occupied spare room & en-suite bathroom?

  1. #1
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    Default Minimum Temperature - sledom occupied spare room & en-suite bathroom?

    I have been giving the issue of the minimum temperature for seldom occupied rooms some thought.

    I live in a 4 bedroom, 3 bathroom house, 2 of which are en-suite. The house was a one up, one down, ancient farmhouse, extended four times between c. 1800 & 1980. The roof & most wall insulation is excellent, & the house has partial double glazing. The house is centrally heated with a gas, wet system, and Evohome throughout & a couple of electric UFH zones, which are not relevant to this question.

    I have one bedroom & en-suite bathroom which are probably used twice a month for a couple of nights. I have been setting theHR92s in both rooms to a permanent 12 degrees, but note that in the recent cold snap the heating was on from time to time, and over shot to as high as 14.5 degrees.

    I tried turning the required temperature down to 10 degrees, it's now overshooting to c. 11.5..

    I then turned the heating off in these rooms for 3 days, and the temperature fell to 5 degrees, ambient was down to 0 overnight at this time.

    The question is, what is the best temperature to set as "permanent" in these rooms whilst they are unoccupied? I always have at least 24 hours notice of when they are going to be occupied.

    Second question, how do I minimise overshoot ?

    What do you do?

    FB

    Tried to edit the typo in the heading, without success !
    Last edited by FullBore; 2nd December 2017 at 09:23 AM. Reason: Expanded...

  2. #2
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    We have a couple of bedrooms and a living room currently unused. I set them all to 5'C permanently and that seems to work fine. In all but the very coldest nights they just coast around high single figures.

    I'm also interested to hear about minimising overrun. I've noticed it in most rooms.

  3. #3
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    My underused bedroom is set to 10c and the heating rarely if ever comes on. 10c is also the overnight temperature for the rest of the house. I used to see temperatures overshooting but that was when I had optimisation configured. That has been off for a long time now and the heating simply comes on and goes off as it should and any overshoot is marginal.

  4. #4
    Automated Home Legend paulockenden's Avatar
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    I use 13 degrees.

    Yes, it uses a tiny bit of gas then for a few weeks a year (not that many), but avoids problems with condensation, mould, etc.

    Not just the room fabric either, but the things stored in those rooms.

    P.

  5. #5
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    Could your over shoots be caused by heat leakage from other parts of the house rather than its own radiator.? I guess you need to see if that room is actually demanding heat and hence going past the set point.
    Last edited by bruce_miranda; 2nd December 2017 at 11:47 AM.

  6. #6
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    I'm guessing it's overshooting as it's not getting any time to learn the charactristics of the room and boiler. If it gets turned on and it's cold outside and low temp to begin with and boiler is turned up, then it will pump the room full of heat, turn itself off and as there is lots of heat in the radiator probably overshoot. Now, next time you use it, it might be warmer outside, but boiler turned down low. As you only have it on a couple of days at a time infrequently, it's probably never gettting a chance to learn the dynamics of the room etc.

    Try leaving the room on for a week or so and see if that helps it learn it better.

  7. #7
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    Also be aware that some rooms, if they are either without two or more external walls, tend to retain heat often above the set point. I have a house bathroom which is always the highest overnight temperature (normally four or five degrees above other rooms) because it is enclosed on three sides by other rooms and the single external wall is east facing (somewhat protected from S-E winds/weather.

  8. #8
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    We have several rooms with HR92s that are unoccupied for several weeks at a time. The set temperature is 13deg. The system was recently installed but during a warm period when the rooms did not require any heat demand. During the current cold spell I’ve noticed a slight overshoot of max 1.5 deg which for me is pretty acceptable given also the system is still probably adapting.

    Also it’s worth checking the “actual” room temperature. The HR92s do a good job as sensor, but my ( limited ) experience is that they do not always represent the central room temperature perfectly, irrespective of how much you try to calibrate them. Eg a HR92 measured “overshoot” due to proximity to the radiator may not actually be reflected in the room.

  9. #9
    Automated Home Ninja Dan_Robinson's Avatar
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    Don't mistake overshoot for thermal gain from adjacent rooms.
    Kind Regards - Dan Robinson (Jennings Heating Ltd)

  10. #10
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    In my experience overshoot happens more often at lower set points than higher set points.

    This is because at a lower room temperature you get more heat output from the radiator for the same panel temperature (greater temperature differential from radiator to room) but less heat loss from the room. (Less temperature differential from room to outside) Warm adjacent rooms will also bleed some heat through into the room.

    Personally I wouldn't worry about a temporary 1.5 degree overshoot of a room set to a low temperature like 14 degrees - its inconsequential.

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