Heat in the home

[jois]

If you have a cold day and have heated bricks outside your home that you want to bring inside to warm your home overnight, you will be opening and closing the door repeatedly, losing heat as you do that.

We have large south facing windows that result in warming of the south facing rooms on cold but sunny days. We keep the curtains wide open on those days and it makes a big difference. On hot summer days we keep the same curtains drawn to keep sunlight out. The curtains are also thick, making them insualtors too. Curtain management is a significant part of our temperature control regime.

Do those techniques really work? I've never been able to picture (using my 6th form physics of 55 years ago) how closing the curtains can make any difference to heat loss or gain in a house from radiant heat (the sunshine) coming through the window glass. Once the radiant heat is caught in the house (by the furnishing, walls, etc. or just the closed curtains) it'll heat whatever it shines on to excite their molecules so they produce heat that'll get convected, won't it? The house air is heated by the warmer furnishing (including curtains) and the house warms up. Perhaps the curtains are made of reflective foil, though? Or perhaps the curtains store a great deal of the heat, only warming the air a wee bit compared to what the sunlit sofa would?

To prevent inner house heat gain from sunshine on the windows, you'd have to have the curtains (or shutters) outside the window, wouldn't you?

But I await a better education of the physicals, should someone (we might guess who ) like to provide it.

Cugel

They will reflect a great deal of the light back out again, dependent on the colour of the curtains, certainly foil lined ones would work best, black, black out curtains worse.

The heat that makes it as far as the gap between curtain and window is held to the most part in contact with the window which allows it to escape by conduction through the glass. Which is generaly the weak point even with double glazing.

Light that makes to the room is reflected of various surfaces at and angle and stays to the most part in the room and so does it's heat,, every surface it bounces off gets a mite warmer

[reohn2]

Al are your windows double glazed?
I seem to recall you saying you weren't allowed due the house being grade two listed.

FWIW,our SE facing living room has a 2.1m x 0.9m and two 0.5 x 0.9m Velux windows,both DG(20mm air gap in the large window and 10mm in the Velux's)in the vaulted half of the ceiling,the room is like a hot house in summer or winter when the sun is shining.Closing the Venetian blind on the large window cools the room from the sun's heat.
I put full cavity insulation in all voids and cavities when I rebuilt the house in 2002

[al_yrpal]

We dont have double glazing but one window, the kitchen where its warmest from the Aga has secondary glazing. Its a window where the view doesnt matter.

Secondary glazing

The sitting room window is single glazed, and you can see the blue insulated blind. We love the view of the garden and dont want it spoiled by secondary glazing. Double glazing isnt allowed here but we could install secondary glazing.

Sliding sash with insulating blind

I wonder if we might be allowed very thin air gap double glazing but as you can see replacing these huge (8ft high) windows would cost a small fortune.

Best heat investment recently was getting the Aga serviced by someone who knew what they are doing. They found a small gas leak and replaced the thermocouple this has resulted in a 25% saving in gas.

Al

[jois]

We dont have double glazing but one window, the kitchen where its warmest from the Aga has secondary glazing. Its a window where the view doesnt matter.

IMG20221003125405.jpg

The sitting room window is single glazed, and you can see the blue insulated blind. We love the view of the garden and dont want it spoiled by secondary glazing. Double glazing isnt allowed here but we could install secondary glazing.

IMG20221003125438.jpg

I wonder if we might be allowed very thin air gap double glazing but as you can see replacing these huge (8ft high) windows would cost a small fortune.

Best heat investment recently was getting the Aga serviced by someone who knew what they are doing. They found a small gas leak and replaced the thermocouple this has resulted in a 25% saving in gas.

Al

You could bung a peice of plastic glass ove that for the winter, not quite as good as double glazing but a lot better than you have and signifantly cheaper

People have had reasonable results with clear wrap and a hair dryer

[Nearholmer]

Sliding sash with insulating blind

I would have thought that you could create a discreet, removable secondary glazing panel using Perspex in a suitable frame, but might that create condensation problems? It would be a disaster to get dampness sitting on that lovely bit of woodwork causing mildew and rot.

Is the problem draught, or is it simply the conduction through the glass that you’re worried about? If the latter, it might be worth running the calculations for the whole house, because you might find that the windows contribute less to the losses than instinct is telling you, so that dealing with them may not make as much difference as you hope. If the walls have no cavity, or do but it isn’t very effective, you might find that it is the walls that are the problem, likewise loft insulation.

[mjr]

We know some folk who have constructed a highly insulated eco house in the Georgian style. It looks wonderful but in high summer its hell because it it slowly heats up and wont cool down making the bedrooms unbearable. They are going to have to install air conditioning.

How does that work? If it is highly insulated, it shouldn't heat up that much. I wonder if someone is opening the windows in full sun, possibly even only at the bottom for maximum heat.

[Nearholmer]

Our house is heavily insulated, and overheats on the top (of three) floors in summer, especially one room which has a large window facing west, which despite being double glazed picks up a lot of solar gain in the afternoons. In warm weather I’m forever fighting a loosing battle trying to get airflow on the top floor to disperse excess heat in the evenings.

To make a building balance in heating/energy terms you have to not only insulate it but put external shading (brise soliel, shutters etc) on it to prevent unwanted solar gain. If you look at either traditional buildings in the med and Middle East, or the fancy modern equivalent built by the Building Research Establishment, you can see the principles, and a British Georgian-looking house doesn’t cut the mustard unless it is fitted with external shutters.

[pwa]

If you have a cold day and have heated bricks outside your home that you want to bring inside to warm your home overnight, you will be opening and closing the door repeatedly, losing heat as you do that.

We have large south facing windows that result in warming of the south facing rooms on cold but sunny days. We keep the curtains wide open on those days and it makes a big difference. On hot summer days we keep the same curtains drawn to keep sunlight out. The curtains are also thick, making them insualtors too. Curtain management is a significant part of our temperature control regime.

Do those techniques really work? I've never been able to picture (using my 6th form physics of 55 years ago) how closing the curtains can make any difference to heat loss or gain in a house from radiant heat (the sunshine) coming through the window glass. Once the radiant heat is caught in the house (by the furnishing, walls, etc. or just the closed curtains) it'll heat whatever it shines on to excite their molecules so they produce heat that'll get convected, won't it? The house air is heated by the warmer furnishing (including curtains) and the house warms up. Perhaps the curtains are made of reflective foil, though? Or perhaps the curtains store a great deal of the heat, only warming the air a wee bit compared to what the sunlit sofa would?

To prevent inner house heat gain from sunshine on the windows, you'd have to have the curtains (or shutters) outside the window, wouldn't you?

But I await a better education of the physicals, should someone (we might guess who ) like to provide it.

Cugel

Like yourself, I have pondered the physics of it. But it does work. On a sunny day, even in winter, the difference in room temperature with cutains closed or curtains open is dramatic. Perhaps the key thing is that our curtains are lined, so the surface facing out is a light calico colour, not far off white, and reflects most of the light back through the glass without it being converted to heat as it would be if it hit a dark coloured surface.

[Debs]

We know some folk who have constructed a highly insulated eco house in the Georgian style. It looks wonderful but in high summer its hell because it it slowly heats up and wont cool down making the bedrooms unbearable. They are going to have to install air conditioning.

How does that work? If it is highly insulated, it shouldn't heat up that much. I wonder if someone is opening the windows in full sun, possibly even only at the bottom for maximum heat.

If it's the bedrooms and upstairs that becomes too hot, it sounds more like the loft temperature has become far too high in the heat-wave sun, and which in turn transmits heat though the loft floor insulation down thought the bedroom ceilings. Loft insulation becomes saturated in very high temperatures and doesn't insulate the heat from passing though to the rooms below.

The fitting of a radiant barrier on the loft joists may help keep the upstairs cooler in a summer heat-wave, but this is not likely to help keep the home warmer in the winter months.

[pwa]

Presumably solar panels on the roof would prevent the roof heating up from direct sunlight.

[Nearholmer]

On a sunny day, even in winter, the difference in room temperature with cutains closed or curtains open is dramatic

My guess is that you are creating a big pocket of warm air between the windows and the curtains, the curtains only passing it on very slowly into the room. A light liner on the curtains will reflect some light back out through the window, but most of the incoming light will warm the curtain and the air pocket, and the resulting infrared radiation won’t pass back out through the glass (greenhouse effect).

[pwa]

On a sunny day, even in winter, the difference in room temperature with cutains closed or curtains open is dramatic

My guess is that you are creating a big pocket of warm air between the windows and the curtains, the curtains only passing it on very slowly into the room. A light liner on the curtains will reflect some light back out through the window, but most of the incoming light will warm the curtain and the air pocket, and the resulting infrared radiation won’t pass back out through the glass (greenhouse effect).

I have touched the outer surface of the curtains on a hot day and they do not get very hot. They get a little bit warm, but no more than that. So most of the sunlight is going back the way it came. During the summer heatwave the south facing rooms, with a large area of glass, stayed tolerably cool with all the windows closed and the curtains closed too. That was over days and days, so we could not simply have been trapping the warmth between curtain and glass.

It would be a different story if the outer surface of the curtains were not nearly white.

[Nearholmer]

They must indeed be reflecting a high proportion of the light.

[pwa]

They must indeed be reflecting a high proportion of the light.

We have a small motorhome that employs the same tactic with its plastic (polycarbonate?) windows, where the frames have neatly built-in blinds that work have a foil outer surface to chuck sunlight back. And together with the insulation in the walls, this does keep the inside from getting hot on sunny days.

Perhaps we pay too little attention to windows normally. We get double glazing and think the job is done, but playing around with blinds and curtains, of the right sort, can help regulate room temperature.

Our hallway has the glazed front door at one end, with a glazed panel at the side. And on the inside of this we have a curtain pole just below ceiling height, and thick curtains that can be drawn to cover the whole door area, from wall to wall, when night comes. One extra bit of insulation for comfort.

[Nearholmer]

Yes, this is all making me think about putting a different blind over the big widow that causes trouble on our top floor. Maybe if I swapped it for a highly reflective one I could reduce solar gain in that room.