1 edit | Fan in window - blow in or out? Imagine a single upstairs large room in a finished garage with windows on the front and back. With one front window open, and a box fan mounted in that window, and two windows in back open, is it better to use the fan to blow cooler air in or exhaust the hotter air out?
While blowing in gets immediate cooling you can feel, most of all if you are in front of the fan, one wonders if exhausting the hot air is better due to the two open windows across the room which would allow two sources of inputted cooler air. |
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 PacratOld and CrankyPremium,MVM
join:2001-03-10
Cortland, OH | Re: Fan in window - blow in our out? When cross-ventilation is readily available, I have always used a fan to exhaust the hot air and draw in cooler air from the other windows.
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Sometimes I think it's a shame... When I get feelin' better when I'm feelin' no pain |
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horsemouthPlease Clarify My CSPPremium
join:2002-03-13
canada | reply to Ken Peterson
We don't have have AC so we use fans often.
We always blow the hot air out but sometimes move the fans around if the wind changes direction.
Not scientific but it works for us. |
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 SandSharkLong may you runPremium,MVM
join:2000-05-23
Santa Fe, TX
kudos:3 | reply to Ken Peterson
Window fan tips.
»m.wikihow.com/Use-Window-Fans-fo···-Cooling |
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| reply to Ken Peterson
Since room is upstairs blow the (warm) air out. Ideally you open all doors/windows except the windows in the "exhaust" room to increase the flow. |
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 ChinaboundPremium
join:2002-12-21
Antioch, IL
kudos:3 | reply to Ken Peterson
Having the fan(s) blowing the air in has always cooled a room much faster than using them to exhaust hot air out.
My uninsulated, windowless 40x60 steel outbuilding has a reversible fan near the peak of the rooftop . It would take forever to draw the hot air out of the building versus having the fan blowing inward.
I feel an immediate change in the temperature with it blowing inward, and felt nothing with it exhausting. |
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 nunyaWho is John Galt?Premium,MVM
join:2000-12-23
O Fallon, MO
kudos:8 | reply to Ken Peterson
Yes. |
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peterboroAvatars are for posersPremium
join:2006-11-03
Peterborough, ON | reply to Ken Peterson
Depends on the prevailing winds as well to aid in cross ventilation. Normally you would exhaust out. |
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| reply to Chinabound
said by Chinabound:Having the fan(s) blowing the air in has always cooled a room much faster than using them to exhaust hot air out. My uninsulated, windowless 40x60 steel outbuilding has a reversible fan near the peak of the rooftop . It would take forever to draw the hot air out of the building versus having the fan blowing inward. I feel an immediate change in the temperature with it blowing inward, and felt nothing with it exhausting. Obviously, since it is a windowless building you are talking about, exhausting out isn't going to be better than blowing air in. If you're blowing out of a windowless building, there is no where for you to pull in air so you'd feel no cool air. |
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 UHFAll static, all day, ForeverPremium,MVM
join:2002-05-24 | reply to Ken Peterson
the age old question, are you supposed to blow or suck? |
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 Radio ActiveMy pappy's a pistolPremium
join:2003-01-31
Fullerton, CA | reply to Ken Peterson
I use one for exhaust in our hobby room, because I don't want cigarette smoke to linger AS MUCH as without. I use the AC (fan only) to supply fresh air throughout the house.
We also have an exhaust fan in our bedroom and one in the living room, the only rooms in which we smoke.
It works well, as I can see the smoke heading right out the window, but I know SOME odor will linger. 
It it gets too warm in the house, we use floor mounted swing fans as an adjunct, or the AC. 
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I can't think of a good posting .sig |
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scross
join:2002-09-13
Cordova, TN | reply to UHF
said by UHF:the age old question, are you supposed to blow or suck? And the obvious answer, of course, is to try both and see which one you prefer!  |
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 MsradellP.E.Premium
join:2008-12-25
Louisville, KY
 ·AT&T U-Verse
| reply to Chinabound
said by Chinabound:Having the fan(s) blowing the air in has always cooled a room much faster than using them to exhaust hot air out. My uninsulated, windowless 40x60 steel outbuilding has a reversible fan near the peak of the rooftop . It would take forever to draw the hot air out of the building versus having the fan blowing inward. I feel an immediate change in the temperature with it blowing inward, and felt nothing with it exhausting. What you're actually feeling is the cooling on your skin caused by air moving across it. Since the fan is so far away you don't feel the air flow when it's exhausting. Assuming you crack the door or some other place for air to move in pulling air out will definitely lower the temperature of the room more. |
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ChinaboundPremium
join:2002-12-21
Antioch, IL
kudos:3 | A door is opened on the opposite end of the outbuilding allowing for exhaust.
It seems to me a fan blowing in cooler air is not only exhausting hot air out at the other end, but it is also cooling the warmer air exposed to the cooler air being blown in.
Does that make sense? |
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 koolman2Premium
join:2002-10-01
Anchorage, AK
1 edit | reply to Ken Peterson
Exhausting would cause the cool air to flow in much slower from the other window. This allows the air to settle and create a temperature differential between the ceiling and floor. Blowing the air in would force the air to mix immediately, cooling the room more evenly. Both methods get the job done eventually, but without supplemental air movement (such as a ceiling fan), it would seem that blowing in would be more immediately effective.
IMHO of course |
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bbear2Premium
join:2003-10-06
94045
kudos:3 | reply to Ken Peterson
This is the same issue that comes up with regard to cooling a desktop PC. Mind you, I'm not calling your living space a box but the concepts are the same. They both have "heat generators" within.
If you can only have one port and one fan; then you need to suck hot air out. If you blow air in, you will create a positive pressure inside the box and the cooling capacities will be greatly diminished - you might feel comfy from the persperation evaporation as someone mentioned, but the cooling effect in the box/room will be limited.
If you have two ports / two fans, then the "stronger" fan needs to be exhaust, sucking air out. And the best you can use the weaker fan to blow in and create a cross flow ventilation the better. If the blow in fan is stronger, then you will again create the positive air pressure situation inside the box/room (see above) - and reduce the cooling capacity. |
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| reply to Ken Peterson
I'd say based on the attached image you want to suck air out. |
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| reply to Ken Peterson
Exhaust the hot air. |
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 mix
join:2002-03-19
Utica, MI | reply to Ken Peterson
Unless you are sitting in that room and like the feeling of cool air blowing on you (this is the point of a box fan), you aren't moving enough air to make that much difference in an exhaust configuration. Furthermore, unless you know which way to breeze outside is blowing, you maybe working against the natural airflow from the wind that enters your room. I think you are better off just leaving all the windows open and only turning the fan on when you are in the room and want a cool breeze to hit you. |
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| reply to Ken Peterson
If the window with the fan is on the shaded side of the building, then draw air in. If it is on the sunny side of the building, then exhaust air out. |
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