At the moment I have a thermostatic switch and a desk fan placed at a side window which to some extent regulates the rooms heat, however there are some problems. 1) Window needs closing at night and when we go out for security. 2) It circulates far too much air so complaints from wife it is damaging point setter plant. 3) If the air at outside of house gets hotter than inside the fan still runs. Using a core drill to make a hole would allow air to be drawn in without the security issue, and if placed at the right height it could also be used for one of those portable air conditioning units, however there are some unanswered questions. Cheapest air conditioner is around £300 so I want to spend less than that if not cooling air but just pulling it in from cool side of house, so looking at around £100 limit not including items also required for air conditioning unit. The fan needs to run in the reverse direction, so flaps used with tumble driers and bathroom extractors will not work, so what can be done so in Winter it is fully sealed? Can be manual as only needing opening and closing twice a year. Next is control, I am using a STC-1000 which I built up for beer brewing, the Inkbird ITC-308 has replaced it now as ready built, but looking at £15 to £25 for a simple thermostat with a remote sensor, the Flowmasta 22199SX wired digital programmable thermostat I suppose could be set mornings only so if off by 11 am unlikely to blow in hot air when outside is hotter than inside. Or two thermostats one switch off if outside over 20˚C and the other inside turning it on when inside over 22˚C. Ideal would be one which switches if inside hotter than outside but for them price goes up. Cheapest room thermostat around £12 digital around £28 likely the cheap one would actually be better, as it would run for a reasonable time, although there is a delayed start set on the STC-1000 there is no delay on stop, so some times fan runs for just a few turns. So type with compensation heater clearly left disconnected may actually work better? So one what height is the vent on air conditioners so I can bore hole to match them if I latter abandon this idea, two what fans can run forcing air in, three what can be done to seal hole in winter, four how best to control, and five can it be done cheap enough to be worth while?