When -on a hot day- the sun is incident on a window covered from the outside by a closed window shutter, the resulting heat is absorbed by the layers of air surrounding the shutter, subsequently circulating upward by convective motion thus drawing in new cooler air from below to cool down the shutter. If instead a curtain was shut on the inside of the window (window shutter absent in this case), the same heating of the surrounding air occurs, but this time around this air is tapped from the interior atmosphere of the house and thus it screws up the overall insulation of the house's interior conditions from the outside. To (partially) offset this effect, one is forced to pick light-tainted curtains. Even then, it seems to me that in a sunnier climate, curtains are going to shed more particulate matter into the surrounding room and thus adversely affect the air quality?

Q: Is this a legitimate/complete assessment? Have I overlooked something?

  • 3
    $\begingroup$ Keeping the sun outside is better in terms of keeping the room cool, so shutters... $\endgroup$
    – Solar Mike
    Commented Jul 7, 2019 at 13:38

1 Answer 1


There are two advantages for having a curtain versus not.

  • Even though the curtains absorb and convert sun's energy into infrared heat, but because of their relative small mass they can not absorb much energy radiated by the sun light, as opposed to sun heating up the entire room and its contents.

  • The little heat generated by the convection around the shades goes up directly without interface with the space used by people.

In designing the interior heating and air conditioning it is beneficial to limit the controlled air space to the space used by people and save energy.


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