A grey Monday morning. You are about to leave for work. It will be dark when you get home.

Do you

a) go round and open all the curtains, and a bit of light through the windows might warm up the house a bit

b) leave the curtains closed, which might keep any existing warmth in?

Your house is east/west facing, for what it’s worth.

If the winter sun isn’t strong enough to heat the UK much above 10 degrees I don’t see how it’ll help to heat your house through the windows.

Curtains closed, I.e insulation, keep the heat in. And have the heating on low all day, otherwise you’ll waste energy trying very the house warm again.

If the winter sun isn’t strong enough to heat the UK much above 10 degrees I don’t see how it’ll help to heat your house through the windows.

It would be a fair point if you had the north winds blowing through your front room. Even in North of Scotland solar gain in winter is a thing how ever a large part of this would be dependant on your weather forecast an when you expect to be home…..you’d have to be home before dark in order to get the blinds closed and capture that gain.

And have the heating on low all day, otherwise you’ll waste energy trying very the house warm again.

This is not true. Maintaining a steeper energy gradient all day in an unoccupied house will waste energy.

Curtains closed would be best, at this time of year… I think.

We’ve just had big bifolds fitted in our kitchen and two weeks ago I went round with my IR heat gun seeing how the glass was performing.
It was a sunny morning. I first tested the existing east facing double glazed kitchen window which is quite old and has a small gap between the panes…. 13c.
I then tested the east facing bifold glass (only double glazed but big gap)…. 17c and climbing!
So solar gain is a definite thing and especially with newer glass panels.
If it’s going to be sunny, open the curtains.

not long after my original post, I noticed that a thermometer in the spare room was in direct sunlight (the clouds had cleared for a bit), and was at nearly 22C. I moved it into the shade and it fairly quickly dropped to about 18.5C.

I am not sure what this proves, except perhaps that the sun is warm.

Foret about it and turn up later in thick sweater, furry Crocs, and nurse a bottle of Jamesons with slanket on standby.

This is the kind of thing automated smart blinds/curtains would be good for, other than laziness.

Paint all of your furniture black for maximum solar absorption.

And automatic opening windows. I wish there was a way to open up the windows for an hour or 2 before te warmest part of the day, then close them when it’s warmest, then close curtains a few hours after that. Then fire up the quatro or combo boiler with a ramp on The hw circuit so it chugs after around at say 50c for an hour, then ramps up the rads to say 60c
All doable with. Microchip technology, hive etc but would be tricky to link it to BBC weather forecast so might require manual setting every day which would be a ballachep

BBC weather forecast so might require manual setting every day which would be a ballachep

A weather compensator is already an option on Vaillant boilers. Assume similar is available from other manufacturers

This is not true. Maintaining a steeper energy gradient all day in an unoccupied house will waste energy

+1 from someone who has a degree in Energy Technology and Management albeit from 30yrs ago, the laws of physics don’t tend to change all that much.

turn up later in thick sweater, furry Crocs, and nurse

I read this as “turn up later in thick sweater, furry Crocs, and a nurse”

Which seems to me to be a very excellent way of keeping warm…

Solar gain is a definite “thing”, there’s a huge difference in our house between a sunny winter’s day and a dull grey one. I might have got short and long the wrong way round in the following …

The short wavelengths of sunlight enters through the windows and heat the furnishings inside. These then emit heat in the form of long wavelength light which is reflected back into the room by the glass so the room continues to heat up.

I’m in a small flat with lots of southish facing glass. If its a sunny winter day then its all curtains open. Can heat the flat up by a few degrees.

In the summer I have reflective curtain things. A bit like mylar. Only way to keep temperatures controlled with so much south facing glass.

I have a long thin house, the long back is south facing. My kitchen has 2 sets of bifolds, and in spring gets quite warm in sunny days due to the low sun angle.

In summer with the high sun it has less of an effect.

Maintaining a steeper energy gradient all day in an unoccupied house will waste energy

There’s a hypothesis I’ve read, can’t find it now and it may only apply in a few specific circumstances, if at all. It’s that allowing the building to cool moves the dewpoint from the outer skin of the wall to the inner, so condensation occurs in the wall. The latent heat from that condensation is lost while the building is unoccupied, but when the heating is turned on later it has to evaporate that condensation. I have not done any calculations to verify this, although I tend to think that the heat lost due to the steeper gradient would be greater that than required to evaporate the condensation, so it may just be a myth.

Regarding solar gain and opening windows, the Gherkin (30 St Mary Axe) has vertical glazed shafts that spiral round the building. Solar gain can be controlled by opening and closing blinds in the part of the spiral in the sun, and cooling by opening windows, all automated.

In practice it’ll depend on a lot of things but, in the most basic terms, closed until Sun is properly up (about 10am in winter) down as the sun starts to dip (at about 2pm.)

In reality hvac savings from properly integrated blinds are fairly small in a domestic property compared with a commercial one simply down to how people use them. (unless you remove user control about 6:1 in practice though very similar on paper for a given property)

Heating on all day can work if your house is well insulated and full of thermostats. It should result in rarely coming on, just odd top up of heat. Same in the evening when occupied.

Technically it’s not really “on” most of the time that way.