Minimum Overnight Room Temperature

Jaith

I'm looking for advice on the minimum room temperature to keep unused rooms at overnight, which keeps the house in good condition and avoids damp and mold and associated house and health problems. I'm not focused on the bedrooms, rather on all other rooms which are unoccupied at night.

I've spent quite a while researching this, but to my surprise given the huge increase in energy bills there is almost no scientifically based advise - what I can find is mostly peoples own preferences or anecdotes about how someone’s grandmother lived to 95 and never set the heating above 10C in winter.

I realise that millions of people won't have any choice but to ration heating as much as possible, but having done that years ago as a student and when first renting, I saw how it can cause severe damp problems and can damage the plaster and even the brick walls over time (and I appreciate that decades ago the draughiness of a typical house made damp problems less likely). I also have seen mold build up and I know how harmful this can be to health. So to be clear I'm looking for the minimum point which generally avoids long-term house damage and health problems.

I've found a few references to keeping things to 15C if possible even in unused rooms, in some guidance from councils, but they don't provide any sources or go into much detail. I've always followed this 15C advice as it's the best I could find, but parts of my house are very old single brick so I could save hundreds of pounds this winter by setting them to 10C or 5C in the upcoming winter - and because they lose heat so easily, in mid-winter they almost certainly would fall below 10C on colder days. Is it a good idea though if I consider the long-term impact to the house and health?

Reed_Richards

I think propensity to damp and mould might well depend on humidity and that can depend on where you live (so how humid it is outside) as well as how well-ventilated your inside is.

MattMattMattUK

Jaith said:

I'm looking for advice on the minimum room temperature to keep unused rooms at overnight, which keeps the house in good condition and avoids damp and mould and associated house and health problems. I'm not focused on the bedrooms, rather on all other rooms which are unoccupied at night.

I've spent quite a while researching this, but to my surprise given the huge increase in energy bills there is almost no scientifically based advise - what I can find is mostly peoples own preferences or anecdotes about how someone’s grandmother lived to 95 and never set the heating above 10C in winter.

It depends on a range of factors, what is in the rooms, the construction of the property, ventilation, humidity etc. If the room is empty and has no plumbing then no heating would not be an issue at all in UK climate, if it has undrained pipes going through it, central heating, taps etc. then it would need to be kept above freezing. Most fridges and freezers do not function properly when the ambient temperature falls below 16c, some freezers are rated down to 2c. Other tech can be fussy about low temperatures, or temperature cycling, one of the main reasons being condensation on internal components, but it can also cause stress due to expansion and contraction cycles, and other tech (OLED) does not work well at low temperatures either, other display technology may also not function correctly. 

Jaith said:

I realise that millions of people won't have any choice but to ration heating as much as possible, but having done that years ago as a student and when first renting, I saw how it can cause severe damp problems and can damage the plaster and even the brick walls over time (and I appreciate that decades ago the draughiness of a typical house made damp problems less likely). I also have seen mold build up and I know how harmful this can be to health. So to be clear I'm looking for the minimum point which generally avoids long-term house damage and health problems.

Mold only grows because of damp, but is generally inhibited at low temperatures, black mold (the worst kind) requires a minimum of 20c to grow. Damp can be damaging to the structure of the building, but is not an issue with cold, so much as ventilation, for much of modern history, before central heading damp was not a problem even without heating, because homes were well ventilated, without heating there needs to be good ventilation otherwise damp will build up and cause issues. A dehumidifier can also help, but they cost money to buy and to run.

Jaith said:

I've found a few references to keeping things to 15C if possible even in unused rooms, in some guidance from councils, but they don't provide any sources or go into much detail. I've always followed this 15C advice as it's the best I could find, but parts of my house are very old single brick so I could save hundreds of pounds this winter by setting them to 10C or 5C in the upcoming winter - and because they lose heat so easily, in mid-winter they almost certainly would fall below 10C on colder days. Is it a good idea though if I consider the long-term impact to the house and health?

Part of that will be because thermal conductivity within the building also has an impact, the insulation from one room to the next is usually far lower than the insulation between indoors and outdoors. In winter an unheated conservatory can drop close to freezing, there is no real ill effect from that because of the nature of the construction. When you say "very old single brick", do you mean single skin modern size bricks, or do you mean an old single brick wall that is 30+cm thick? I would suspect that insulation may be your friend far more than letting the internal temperature drop to 5c.

Alnat1

Are you talking about living room/dining room/kitchen that will generally be heated anyway during the day?

I've never had the heating on overnight in any property I've lived in. If the house is fairly well insulated and heated during the day it's unlikely to drop lower than 12-14C even in the coldest weather. I've always set heating to come on half an hour before I get up and to go off an hour before bedtime.

Jaith

Thanks for the replies, especially Matt - that's lots of good info I haven't come across before.

It sounds like I can get away with <15C without any damage, and I need to test for my own conditions the point at which I'd start getting damp. I do have an old dehumidfier which would probably be cheapish to run if it it let me get away with less heating, but ideally I wouldn't have one in every room.

MattMattMattUK said:When you say "very old single brick", do you mean single skin modern size bricks, or do you mean an old single brick wall that is 30+cm thick? I would suspect that insulation may be your friend far more than letting the internal temperature drop to 5c.

It's 1890s construction or so. Sorry I should have said 'solid wall' rather than single brick. It's 300mm thick from memory.

Alnat1 said:

Are you talking about living room/dining room/kitchen that will generally be heated anyway during the day?

Yes I'm talking about rooms that would be be used during the day. You're right that well insulated rooms wouldn't drop much below 15C if other parts of the house were heated, but in the old section with solid walls the rooms lose heat much quicker (the U-Values I've found online suggest around 8 times as fast as modern cavity insulted walls).

GunJack

pedant alert......

it's mould, not mold. Mold is a town in North East Wales

end alert

Swipe

My spare rooms mostly sit around 10C but can go as low as 6-7C during a cold spell. The humidity rarely goes above about 68% and if it does I switch on a dehumidifier

markin

Insurance companies often say 12c.

Remember you breath out and sweat just under a liter per day, so open the bedroom window every morning for 5min.

Mstty

GunJack said:

pedant alert......

it's mould, not mold. Mold is a town in North East Wales

end alert

Maybe the OP has a dodgy "u" key, so ignore spelling issues due to "u"....they blame "u"

theoretica

Get a hygrometer/thermometer and you will be able to see what happens to the temperature and humidity overnight.  It will depend on the weather  - if it is below freezing, the outside air will be dry, for instance.

Ultrasonic

I have my heating off overnight in winter. Firstly to not waste energy but secondly as the noise of it coming on would probably wake me up!