Building designers in cold climates are accustomed to coping with the heat loss from large windows in the winter. Air next to the window is quickly cooled and—being heavier than the rest of the air volume— flows down the face of the glass, billowing into the room in a steady cascade. A common solution is to install baseboard heaters at the bottom of the glass, with either hot water or electric resistance elements. Warm air rises up the window, preventing the cold air from building a uniform flow momentum into a steady-state flow regime.
These baseboard heaters are needed 24 hours a day, even at night when the building is not being heated. Although some building operators might be overzealous and try to save energy by turning the baseboard heat off at night, this may not be an energy saver. With the window heaters off, the exterior zones quickly reach equilibrium with the outside, causing a precipitous drop in temperature that soon cools even the interior zones (which generally would stay substantially warmer than the exterior ones) as high volumes of air cascade off the vertical window surfaces.
Many building operators in more temperate climates, on the other hand, are unaware of this phenomenon and do not guard against it. Any large expanse of glass should be protected, no matter how long the heating season. Finally, in any situation, the heaters should be disabled during the cooling season, so they do not operate in response to the cool air conditioning and waste energy in reheating.