head
the upper horizontal member of a window frame.
back to top

head expander
a U-shaped extrusion slipped over the frame head that, when pushed up, closes the gap between the frame head and the opening head after window installation.
back to top

heat fusion
(welding) method to join PVC frame and/or sash members by heating the cut ends, squeezing them together, and allowing the assembly to cool.
back to top

Heat Mirror™
a triple-ply insulating glass unit (IGU) utilizing a polyester internal film with a special coating to reflect heat, but allows light to pass through. Heat Mirror is a trademark of Southwall Technologies Inc.
back to top

heat treating
the process where glass or aluminum extrusions are heated and cooled to make these materials harder and stronger.
back to top

hermetically sealed unit
an insulating glass unit (IGU) that is sealed against moisture. The unit is made up of two lites of glass, separated by a roll-formed metal spacer tube (at the full perimeter) which contains a desiccant (moisture and/or solvent absorbing material). The unit is then completely sealed, creating a moisture free air space.
back to top

hollow extrusion
a tubular extrusion having an enclosed cavity within it. It is usually stronger, although more costly, than a solid extrusion.
back to top

hung window
a window in which the operating sash move up and down within the master frame. The weight of each operating sash is counterbalanced with balances to permit easy operation.
back to top