A device for counter balancing a sash of a double hung window to hold it in an up position. There are four basic types:
* Block & Tackle - Sometimes referred to as string balance. A type of balance that employs a block and tackle apparatus and coiled spring. This type balance allows the sash to be easily removed from the window frame. A block and tackle balance can normally carry a heavier load than a spiral or friction balance.
* Spiral - A balance using a spirally-wound spring.
* Spring - A balance using a spring for counter-balancing; introduced in the 1980?s.
* Constant Force - A coiled steel tape under spring tension for balancing the sash, located in the head jamb of the window frame.
* Counterweight - The most common type of balancing system in older homes, utilizing a weight held by a sash rope or chain over a pulley.