Glossary

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Hanging sash (also hung sash)
Sash hung on a cord connected to a counterweight.
Header
The upper horizontal member of a window frame. Also called head.
Heat-absorbing glass
Window glass containing chemicals (with gray, bronze, or blue-green tint) which absorb light and heat radiation, and reduce glare and brightness. See also Tinted glass.
Heat gain
The transfer of heat from outside to inside by means of conduction, convection, and radiation through all surfaces of a house.
Heating degree day
Term used by heating and cooling engineers to relate the typical climate conditions of different areas to the amount of energy needed to heat and cool a building. The base temperature is 65 degrees Fahrenheit. A heating degree day is counted for each degree below 65 degrees reached by the average daily outside temperatures in the winter. For example, if on a given winter day, the daily average temperature outdoors is 30 degrees, then there are 35 degrees below the base temperature of 65 degrees. Thus, there are 35 heating degree days for that day.
Heat loss
The transfer of heat from inside to outside by means of conduction, convection, and radiation through all surfaces of a house.
Heat-strengthened glass
Glass that is reheated, after forming, to just below melting point, and then cooled, forming a compressed surface that increases its strength beyond that of typical annealed glass.
Hinged windows
Windows (casement, awning, and hopper) with an operating sash that has hinges on one side. See also Projected window.
Hopper
Window with sash hinged at the bottom.
Horizontal slider
A window with a movable panel that slides horizontally.