Fan not pulling air thru the window?
#11
  
So... bought a new (to us) house this spring and moved.  I work rotating shiftwork (nights, weekends, some days, etc.) and do a non-trivial amount of day sleeping as a result - which is a whole lot easier (for me) with a cool (cold!), dark room.  So ended up putting a window-mount A/C unit in the master bedroom (upstairs); probably going to go with a mini-split next year.  This fall, as the temps cooled to where it's maybe 60 during the day, and in the low 40s at night, I pulled the A/C unit and put it away for the season.  Figured I'd be able to just put a fan in front of the window and things would be plenty cool enough.  Turns out, not so much!

For whatever reason, the fan (pedestal mount, tower style) doesn't appear to be pulling *any* outside air *into* the bedroom.  I've closed off the vents from the rest of the central air system, but the master BR is consistently 5 degrees warmer than the hall way outside, and probably 10 degrees warmer than the down stairs living area.  We've tried various configurations of window cracked, window wide freakin' open, bedroom door cracked/open, downstairs window cracked, etc.  About the only thing I haven't tried yet is putting a box fan in the window blowing *out*, mainly because I'd rather pull the 40-45F outside air into the room, rather than the 60-65F air from the rest of the house (at night) into the room.  I like the BR cold, not the rest of the dang house!

Been thinking that somehow there is a positive pressure on the house, or specifically that BR, that is making it difficult to 'pull' air in thru the window.  But at this point, I'm open to ideas - other than lugging the A/C unit back upstairs!
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#12
  Re: Fan not pulling air thru the window? by nuk (So... bought a new (...)
Do you have a window downstairs open.  The fan has to be able to push the air out
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#13
  Re: Fan not pulling air thru the window? by nuk (So... bought a new (...)
The pedestal fan will take the air from the easiest source which would be the room air. I expect if you could see the air circulation you would see that the air is mostly circulating in a sort of donut or toroid shape around the perimeter of the fan. A box fan in the window would be better, especially if you block off the opening on either side. (Assuming the window opening is wider than the fan.) And you could improve the efficiency even further by blocking off the corners inside the box fan so the air can't easily wrap around the ends of the fan blades.

If you put the fan in your bedroom window blowing in and there's no easy router for air to escape, the pressure in the room will limit how much outside air can get in. Instead of putting the fan in your bedroom window, put it in a window in another room and set it to exhaust the air out the window. Make sure your bedroom window is open wide and no other windows are open.

When I was a kid my dad set up a fan in a living room window which was at the opposite end of the house from the bedroom. At night only the fan's window and the bedroom windows were open so cooler outside air was pulled into the bedrooms and down the hall out through the fan. He used a dryer timer to allow the fan to run for about an hour or so and then shut off. That would cool the bedrooms enough so we could get to sleep. If the fan ran all night it would be often be too cold in the morning.
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#14
  Re: RE: Fan not pulling air thru the window? by fixtureman (Do you have a window...)
(10-16-2019, 10:50 AM)fixtureman Wrote: Do you have a window downstairs open.  The fan has to be able to push the air out

Not trying to push air *out*, trying to pull air *in*.
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#15
  Re: Fan not pulling air thru the window? by nuk (So... bought a new (...)
(10-16-2019, 10:55 AM)DaveR1 Wrote: The pedestal fan will take the air from the easiest source which would be the room air. I expect if you could see the air circulation you would see that the air is mostly circulating in a sort of donut or toroid shape around the perimeter of the fan. A box fan in the window would be better, especially if you block off the opening on either side. (Assuming the window opening is wider than the fan.) And you could improve the efficiency even further by blocking off the corners inside the box fan so the air can't easily wrap around the ends of the fan blades.

Ah... the air-flow pattern of the tower fan might indeed be a significant part of the issue. Makes sense, now that you mention it!

Quote:If you put the fan in your bedroom window blowing in and there's no easy router for air to escape, the pressure in the room will limit how much outside air can get in. Instead of putting the fan in your bedroom window, put it in a window in another room and set it to exhaust the air out the window. Make sure your bedroom window is open wide and no other windows are open.

There's a few complications with that... one being keeping the cat out of the bedroom with the door open at night (doesn't bother me, but drives the wife nuts), or household noise out (when I'm sleeping days on the weekends). Also, the thermostat for the whole house is right there in the upstairs hall way between the bedrooms - pulling cool air through that area past the thermostat would artificially jack up the temperatures in the rest of the house.

Hopefully just getting a fan with a better air flow pattern in the window will help enough.
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#16
  Re: Fan not pulling air thru the window? by nuk (So... bought a new (...)
If air is coming into the room from the window, the same amount has to leave, either go out the window, or some other path.  That's why fixtureman asked about having another window open.  If there's no outlet, then your fan won't pull air in that open window.

As DaveR1 said, the pedestal fan is going to just move air around the room.  It's really not going to pull much air in from outside.

You can get a fan that is designed to fit in the window opening, and it will likely work better.  However, for best efficiency, you'll need to have an path for the air to leave the room as well.  If you need to keep the door closed to that room, and still want to pull air in the window, then there are also double fan units; one can be pulling air in from outside while another is pushing air out.
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#17
  Re: RE: Fan not pulling air thru the window? by WxMan (If air is coming int...)
(10-16-2019, 11:27 AM)WxMan Wrote: If you need to keep the door closed to that room, and still want to pull air in the window, then there are also double fan units; one can be pulling air in from outside while another is pushing air out.

Ah.  I knew there were reversible models, didn't know there were ones that did in and out simultaneously.  Seems like there'd be some mixing / re-circ issues with that sort of setup, with the intake and discharge so close together?
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#18
  Re: Fan not pulling air thru the window? by nuk (So... bought a new (...)
I like to put a fan facing out in one bedroom that we don' use and open windows in the rooms we are in
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#19
  Re: RE: Fan not pulling air thru the window? by nuk ([quote='WxMan' pid='...)
(10-16-2019, 11:42 AM)nuk Wrote: Ah.  I knew there were reversible models, didn't know there were ones that did in and out simultaneously.  Seems like there'd be some mixing / re-circ issues with that sort of setup, with the intake and discharge so close together?

If you use a double fan in a single window, you'll need some sort of baffle to prevent the incoming air being exhausted right out before it has a chance to circulate through the room.
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#20
  Re: Fan not pulling air thru the window? by nuk (So... bought a new (...)
Just put a box fan right in front of the window screen. It will pull cold air into the room without needing to be able to vent air somewhere else.

I swear, you guys can over complicate the simplest things. Laugh
Mark

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