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.Cugel wrote: ↑3 Oct 2022, 9:29amDo 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?pwa wrote: ↑3 Oct 2022, 5:36am 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.
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
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