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  1. #1
    Automated Home Sr Member
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    Default Target temperature for little used rooms.

    I live in a four bedroomed, mostly ancient, detached property in an exposed position.

    There is some, probably 20% double glazing, the remaining windows being 100+ year old sash windows or leaded light. Walls are generally solid & thick, and the roof is exceptionally well insulated.

    Evohome works very well for me but I have been considering target temperatures for two bedrooms & a bathroom which are only used when we have guests, probably 3-8 nights a month in winter. They are currently set to a constant 14 degrees, which they maintain with radiators warming up a few times every day to achieve this. I think I've got it about right but your suggestions would be welcome.

    One thought is to lower the target to, say 10 degrees, and see whether the room temperature drops to 10 degrees, or settles at a higher temperature as a result of the adjoining rooms being at a higher temperature.

    Thanks in advance.

    FB

  2. #2
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    Quote Originally Posted by FullBore View Post
    .... I have been considering target temperatures for two bedrooms & a bathroom which are only used when we have guests, probably 3-8 nights a month in winter. They are currently set to a constant 14 degrees, which they maintain with radiators warming up a few times every day to achieve this.
    Why do you heat them at all? I have guest bedrooms and bathrooms that I leave unheated normally but turn on the heating a day or so before guests arrive so that the furniture and fabrics feel warm on arrival. If you ventilate the rooms after the guests have left and then turn off the heating, you won't get any condensation unless you have draughts through the rooms from other heated rooms, bringing warm moist air into those cold rooms.
    Last edited by Edinburgh2000; 25th October 2018 at 04:27 PM.

  3. #3
    Automated Home Jr Member
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    I think that the unused rooms should be kept at 1 deg above dew point so that the structure stays dry.

  4. #4
    Automated Home Legend paulockenden's Avatar
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    Quote Originally Posted by GreenGuy View Post
    I think that the unused rooms should be kept at 1 deg above dew point so that the structure stays dry.
    Surely unless the RH is 100% the dew point will always be less than the room temp.

    http://www.dpcalc.org/

    Or have I misunderstood what you are saying?

    P.

  5. #5
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    My house is pretty similar to your own with solid walls. The upstairs bedrooms that are not in use have been kept at 5 degrees except when heated up for guests. I have no problems with damp or moisture forming on windows so am perfectly happy with this approach used for the last 7 years (?) with Evohome.

  6. #6
    Automated Home Sr Member
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    Ditto, my two spare rooms are set at 5 degrees with no issues all year.

  7. #7
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    Quote Originally Posted by FullBore View Post
    I live in a four bedroomed, mostly ancient, detached property in an exposed position.

    There is some, probably 20% double glazing, the remaining windows being 100+ year old sash windows or leaded light. Walls are generally solid & thick, and the roof is exceptionally well insulated.

    Evohome works very well for me but I have been considering target temperatures for two bedrooms & a bathroom which are only used when we have guests, probably 3-8 nights a month in winter. They are currently set to a constant 14 degrees, which they maintain with radiators warming up a few times every day to achieve this. I think I've got it about right but your suggestions would be welcome.

    One thought is to lower the target to, say 10 degrees, and see whether the room temperature drops to 10 degrees, or settles at a higher temperature as a result of the adjoining rooms being at a higher temperature.

    Thanks in advance.

    FB
    We have a room that was seldom used, last winter I had it scheduled to 12 degrees when the house was occupied but found that it suffered from dampness problems, especially if it wasn't turned up higher than this at least once a week. There was enough condensation on the window most of the time that mold would start to grow...

    This winter the room is getting used a little bit and I've adopted a different approach - in the morning I warm it up to 20 degrees for about an hour then off (during the week) or back down to 15 for the rest of the day in the weekend, which it does fall to. No problems at all with dampness, not even condensation on the window now and the room smells fresh even when it has dropped to 15 degrees.

    So personally I would make sure that the room spends at least part of the day at 15 degrees or above - it doesn't have to be all day long.

    Quote Originally Posted by Edinburgh2000 View Post
    Why do you heat them at all? I have guest bedrooms and bathrooms that I leave unheated normally but turn on the heating a day or so before guests arrive so that the furniture and fabrics feel warm on arrival. If you ventilate the rooms after the guests have left and then turn off the heating, you won't get any condensation unless you have draughts through the rooms from other heated rooms, bringing warm moist air into those cold rooms.
    Quote Originally Posted by paulockenden View Post
    Surely unless the RH is 100% the dew point will always be less than the room temp.

    http://www.dpcalc.org/

    P.
    Draughts from other rooms. If you keep an empty room at say 10 degrees, but adjacent rooms are 20 degrees, (which takes pretty good insulation between rooms BTW) in the normal course of household activities such as showers, cooking, people breathing etc, the dew point can easily climb well past 10 degrees in the warm rooms. When that warm moist air filters into the cold room it condenses, especially on the window which will be well under 10 degrees even if double glazed. (Just because the air temperature in the room is 10 degrees doesn't mean exterior wall surfaces will be...)

    So at the very least you'll get condensation on the window, if not elsewhere in the room. After a few weeks like that it will start to smell damp...

    So if the room is not air tight from other rooms you can't have that sort of large temperature differential without condensation issues.

    In the end I gave up and keep my unused room at 15C during most of the day when the house is occupied (which doesn't take much gas) and give it a boost to 20 for a short time in the morning to help prevent any accumulation of dampness.
    Last edited by DBMandrake; 26th October 2018 at 12:40 PM.

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