A support system for a heavy sash that is laterally removable from between opposed window jambs includes a pair of sash support arms pivotally mounted on each sash stile and counterbalance shoes that engage the support arms to uphold the sash. The support arms, in inwardly dependent positions, can engage the shoes as the sash is lowered onto the shoes; and the support arms, in outwardly extending positions, support the weight of the sash on the shoes. Hooks dependent from the shoes can lock the shoes to the jambs during sash removal or replacement; and the sash support arms, the shoes, and the hooks are all preferably cut from metal extrusions.