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All but one major room is part of a single path through home, from a window on one end to a window on the other. In the evening I want to bring in cooler outside air as efficiently as possible. If there is no breeze outside, is it faster to

  • close all windows except the two endpoints, setting up the box fan (which fits well in the window) to push air in or pull it out at one end.
  • open all the windows, and put the fan somewhere, without knowing exactly what the path of airflow from it will be.

The first method takes no advantage of whatever minimal passive airflow would occur with all windows open wide.

The second method doesn't make as good use of the fan, because it may end up cycling the air immediately around it over and over instead of reaching all areas of the house.

If passive circulation were truly nonexistent, then maximizing the fan's efficiency would be the way to go. Does it seem plausible that passive circulation could indeed be low enough for that to be the case?

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    It might be difficult to measure accurately with a regular thermometer anyway, because those don't account for heat-loss due to air movement. The best test for you would be to actually try both and stick with the method that makes you feel most comfortable. – Jimmy Fix-it Jul 3 '20 at 0:15
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    why are you asking a question about something that you can easily test for yourself? – jsotola Jul 3 '20 at 1:07
  • Edited the question to improve clarity of what's being asked. – rwusana Jul 3 '20 at 1:38
  • You can open the windows different amounts to balance the airflow - open the ones near the fan less, and farthest from the fan fully, unless you have specific comfort goals that are better served by a different scheme. Or add another fan. – Ecnerwal Jul 3 '20 at 2:33
  • In Iranian architecture, the wind towers – gboffi Jul 3 '20 at 14:11
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Moving air tends to feel cooler than still air. If you can put up with the noise, the box fan trick works quite well.

In my experience, air movement in the home depends on air movement outdoors; if it's a still evening, even with lots of windows open, you won't get much air. On the flip side, even a small breeze can help.

If you have lots of money and live in an amiable climate (cool, dry nights), buying a modern whole-house fan may be a good fit. Modern units suspend the fan itself from the rafters via an insulated duct, and are much quieter than they used to be.

As Jimmy Fix-it commented, the best thing to do is to try both of your methods.

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    A whole-house fan is not THAT expensive, and has the advantage of getting the hot air out of the attic (by blowing the warm air from the ceiling of the house into it, and pulling cold air in the windows to replace that...) – Ecnerwal Jul 3 '20 at 2:30
  • The reason I don't want a half dozen inefficient window AC units is environmental, so I definitely appreciate the efficiency of pulling the air that is naturally hottest off the top of the house. Unfortunately not going to happen in my rented flat. – rwusana Jul 3 '20 at 2:53
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    @Ecnerwal The really nice ones (QuietCool, etc) that don't mount to the framing directly are quieter because they have more hardware to physically remove them from the hall ceiling (damper boxes, insulated duct, etc). You do pay a premium for that. That being said, if you just want to move air, the good ol' helicopter in the hallway will do the job more than well enough! – supertanker13 Jul 3 '20 at 5:32
  • Whole house mechanical extract should never dump air into the loft space, it should always vent outside. The air will be warm but also have humidity from the occupants, during cold weather it will condense in the attic space and rot wooden structures. – jonathanChap Jul 3 '20 at 12:33
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Previously I had a home with no A/C, it was in a forested area so not too bad. But to cool overnight, I put 2 box fans in the living room (great room) windows, both BLOWING OUT. I also blocked off parts that the fans didn't cover in the two windows. Then in other rooms opened windows which allowed cooler night time air to enter the room. I wouldn't use the "push - pull" method you described. It would only function in the immediate room space and probably not do much for the rest of the house.

So the cool night time air entered other rooms (mostly bedrooms) and got expelled via the fans in the living room. Worked pretty well. Sometimes got a little too cold in the BR for the wife, but it worked.

Hope this helps.

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    Yes that's an interesting technique. If I need airflow during the day in my office, I generally draw in air by pushing it out from another room like that so as to keep the noise down for videoconferencing (big 2020 thing, for anyone reading this in the future). – rwusana Jul 3 '20 at 1:13
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If this will be long term, a whole hose attic fan is excellent, I have had them in 4 different houses. Get a belt drive because the direct drives make air noise because of higher RPM ,smaller fans. You can install it in any room although the instructions say to put them in a central location. My present one is in a utility room in the corner of the house and works fine. Open the windows more in the rooms you want the most airflow. Our 24" two speed fan will make it uncomfortably windy on low speed if I only open windows in three rooms. In winter , I did pull off the belt so the fan will not run and lay insulation over the louvers to slow heat loss; but now that I am older ,I don't bother. Noise was only a factor in the one direct drive fan as I made the mistake of putting it in a central location which was a hallway outside bedrooms. Cost was not a factor as I put them in myself and the fans are cheap.

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Because you're renting, I'd close draperies during hottest part of day (light =heat). After sunset, open draperies/windows on both sides and turn on your kitchen exhaust fan in addition to the box fan, to determine if it creates a sufficient draw of cooler air into your home.

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