Posted By John Doe Just wondering whether there are any principles which affect ability to create a through-draught to create air-movement. I guess there's a point where too many open windows and doors means that air movement decreases or plateaus. Any boffins in the through-draught department?

Posted By Lilian McCartney Hi the dr on tv the other day said not to open windows if its very warm outside as the hot air will come in - think you'd have to decide where its hottest, in or out. She also advised freezing a plastic bottle of water and sitting this in front of a desk fan as it will provide cooler air - worth a try perhaps? HSE have item on their home page on hot weather. Like Pete we've had colder weather but the sun is now breaking through!

Posted By Helen Horton New style double glazing with the "K" type glass does keep the place cooler if the windows are kept closed with the curtains drawn to. But (you knew there would be a but) the house feels claustrophically close and hot with no air movement at all with all the windows closed, even the fan doesn't seem to help. I've found that keeping the curtains drawn and windows shut downstairs but windows open upstairs creates a nice breeze and the house "feels" cooler. This must be a subjective assessment as the thermometer says the opposite but without the upstairs windows open it feels really uncomfortable. At night it is a little different - I came down as it was too hot upstairs (all windows open) and opened the patio door and sat outside. When I had cooled down I went back up to bed and found the bedroom a good 3 degrees cooler than before and all I had done was open the patio doors. Now of course I couldn't leave them open for security reasons so had to shut them again and the temperature quickly went back up in the bedroom. Can anyone explain the physics of this as it has me baffled?

Posted By Ali Looking at properties of air is no different to the principles of wave mechanics really as air is a fluid and therefore subject to the same laws eg. waves will travel in the direction of propagation unless the wave front hits an obstacle in which case it will experience reflection, interference etc.that will effectively reduce the "air current". Also, as air warms up it increases it's average kinetic energy and therefore travels faster. Warm air is never really "still" .It only tends to "rise" where it meets cooler air as warm air is less dense. Of course, if it meets warmer air it doesn't rise. High level windows will certainly help to remove warmer air whilst low level windows will allow cooler air in so as to maintain the equilibrium. Fans will only help to circulate the air and mix the different layers. Does this help ? Ali

Posted By John Doe This is really good stuff! What I'm getting is that you need a chimney-type effect to get the whole thing moving; with the emphasis on the top opening(s). Thus pushing out the hot(ter) air from the top. Pretty much like you'd get an optimum amount of dilution ventilation, I suppose. I vaguely recall seeing things called 'wind towers' on houses in the Middle East which must operate on this principle. Thanks for all this.

Posted By Merv Newman The "chimney" effect is right on. It provides draft for fireplaces and the middle eastern "wind towers" are used, if efficient enough, to produce ice even in the desert. So, if you are not on a train, open high and low windows and intervening doors. Security considerations at home may compel you to put some protection at least on the lower windows. Or install air-conditioning. We did it before the last heat-wave and invited all the village OAPs to come and spend the afternoons with us. Kept us up with the village gossip. You should have heard who was doing what with what to whom. (reference to old joke about lesbian lady married to a gay gentleman) And how often ! And in which field ! And that included absent (more heat-resistant perhaps) OAPs 35°C here (95°F, 26.5°R) Merv

Posted By George Wedgwood For those with lofts, a great tip is to open the loft hatch during the heat of the day to allow air movement from downstairs windows up through the house. In the morning 'cool', allow max ventilation until full day temps are reached, then shut the windows and doors and curtains to help insulate the rooms from further solar gain. leave the loft hatch open as hot air rises and it will be really hot anyway but still allow the heated air contained in the house to move up and be replaced by cooler air from the ground floor. The worst thing to do if you have a conservatory, is to open its door into the house and it acts like a heat pump and makes the rooms too hot! Keep it closed to the house during the day and move your bed to the kitchen floor!

Posted By Jack I take it that's Réaumur not Rankine? Can't be - conversion doesn't match.