Ed Pawlowski wrote:

wrote
That's all BOX fans do when used properly too - they are NOT window
fans. Using them as such is a misuse.- Hide quoted text -

- Show quoted text -

Says who?

Harry K
They make window fans for that purpose. Box fans are air movers meant
to sit on the floor.

What happens to them if you sit them on a window sill? I've seen many
used like that; I'd guess millions nationwide are in windows. I've
never seen a caution about not using them in a window.

However, I did find this on Lasko's web site:
http://www.laskoproducts.com/prodinfo/faq-fans.html
Can I use my Box Fan in a window? Most box fans are not designed for use
in a window

Note the word "most" as opposed to using the word "no".

And the don't give any specifics here
What is a Window Fan? A fan mounted in a window to circulate the air.
Window fans are used for air intake, air exhaust, or air exchange. The
blade size ranges from 8" to 16"


A window fan is intended to seal the window space so it can inhale as
well as exhale.

Placed a few inches from a screen, a box fan won't inhale much through
the screen but will exhale very well through the screen. This can be
demonstrated by dangling a piece of toilet paper beside the fan. If
it's blowing toward the screen, there won't be much air movement beside
the fan. If it's blowing into the room, the toilet paper will probably
be sucked toward the screen and into the fan. The viscosity of still
air makes it hard to reach the fan through the screen, so air from the
room is sucked around behind the fan.

When a fan exhales toward a screen, the velocity of the air will carry
it right through. A fan 6" from a screen will do better than one 6'
from the screen because the velocity will be greater at the shorter
distance.

A 20" box fan should exhale twice as efficiently as a 10" window fan.
The smaller fan would have to impart 4 times the velocity to blow the
same volume as the larger fan, and that means 16 times the energy.

I have a couple of loops of cord tied through the top of my 9-pound box
fan. It takes just a moment to hang it from hooks at the top of my
kitchen window, where the air is hottest and most humid and there may be
smoke in the event of a cooking mistake. If I want to cool the house, I
walk outside and feel for any movement of air. If there's air coming
from the direction of that window, I'll put the fan on a table in a
window on the other side of the house. No use fighting Mother Nature.