1) Do window A/C units, when set on the fan only setting, blow fresh air in
from the outside, like a regular box window fan, or recirculate air from the
2) Same question, but with the A/C turned on. Does the air come from the
outside or inside?
Because I have my window A/C set to fan only, and even though it was
freezing outside, it was blowing warm air!
I think few new units have fresh-air intakes, in the name of
efficiency, assuming outside air is hotter than inside air so would
take more energy to cool. A bit of a shame since often the A/C is
blocking the only window that you could open for a breeze on a nice
Thanks Dan! But then why is the filter right along the front (inside the
house) grill of the air conditioner? And why is dust forming on this same
grill? It seems that the AC unit is sucking in air from the inside via the
grill then filter?
Any window unit made in the last 20+ years will have an adjustable flap
that allows some outside air to be mixed in to the room air passing over
the cooling fins. You can adjust it so that it is taking mostly outside
air all the way to no outside air.
For efficiency purposes related to cooling, you would want to close out the
outside air so you are just cooling inside air over and over.
The air comes from the inside. It is pulled through the filter then
the evaporator and blown out the vents above. Some units have a
selector you can turn that will open a small door to let fresh air in
to the stream or to blow stale air out but this would only be a
fraction of the air.
It works the same way. Doesn't matter if the compressor is running or
Yes you are correct that the air is coming from inside. If there is a
fresh air selector on the a/c it opens a little door in the air path
so fresh air from outside is drawn in to the air stream (about 10%)
Thanks Steve and to everyone else who answered! This explains why I am
getting warm air then with the fan-only setting. I had to run the A/C even
when it was cold outside, since the heat inside always runs inside the
house, making the temperature 76-77 degrees F. inside at all times! The
thermostat was fine, but something was wrong with the furnace so it almost
never stopped running, even though the thermostat was set at 58 degrees F.!
But my landlord finally called a furnace tech after a few weeks, at my
insistence, so hopefully this won't go on too long!
I know! When it is not hot enough to run the AC, but you still would like
fresh cool air blown inside, a window A/C unit is basically useless! And I'm
not going to uninstall it and replace it with a box window fan everytime I
just want fan only!
No, the "default" is to recirculate. If the unit doesn't have a "fresh"
switch/lever, then the unit will ONLY recirculate ...
See above ... and it would make little sense to set the lever to "fresh" if
you were attempting to cool the air ... it's kinda hard, in the middle of
summer, for your window unit to cool 95 degree air ...
This is much more of an issue in commerical buildings than anywhere else
(due to the much larger numbers of ocucpants). The average home has, what, 4
people in a 2000 sf enclosure ... unless the home is exceedinly tight,
infiltration and the occasional comings and goings will provide ample fresh
air. And, in this particular case, since the poster is talking about window
units, I'm making the assumption that the home isn't terribly tight ...
Mostly been just the "Kevin and Bill show" there for the past couple
days--hopefully, those nice men with the white coats won't let Matt back out
till his new meds kick in.
IOW, probly fairly safe to go back now...
Basic Principal of Economics Here
All air-conditioners are designed to re-circulate the indoor air. In
addition to cooling the air, the second, but equally as important job
of an air conditioner is to de-humidify the inside air. If they just
sucked in 100% outside air, the cost to cool and de-humidify that
volume of air would be incredible.
The little fresh air vent that has been described on most A/Cs is just
that... A way to provide a little bit of fresh air from the outside
without excessive expense.
Lack of fresh air is why some people feel sick in an air-conditioned
space. Your breathing the same CO2 and other byproducts of human
respiration over-and-over. If not enough humidity is taken out of the
air, you will feel cold and clammy.
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