Sash replacement may be an alternative to a full window replacement or an insert window into an existing frame. The physical condition of the existing window must be good—there should be no moisture or air leakage. An energy auditor or replacement contractor may help you determine if a sash replacement is a viable option based on your homes window and wall conditions.
Many manufacturers offer replacement sash kits, which include jamb liners to ensure good operability and fit. This option allows for relatively easy installation, but the existing frame must be in good shape so that air and water tightness is ensured.