A single-hung window normally has one operable lower sash and a fixed upper sash. A double-hung window has two operable sashes. That changes ventilation and cleaning access, but it does not by itself determine energy performance, durability, or installed cost.
| Issue | Single-hung | Double-hung |
|---|---|---|
| Operation | Lower sash opens | Upper and lower sashes open |
| Ventilation | Opening at the lower sash | Can vent at top, bottom, or both within product limits |
| Cleaning | Exterior of fixed upper glass may require outside access | Many models provide tilt-in cleaning for both sashes; verify exact hardware |
| Service | Fewer moving sash components | More balances, locks, weatherstripping, and moving interfaces |
Compare the exact window
Use the NFRC label for whole-product U-factor, solar heat gain coefficient, visible transmittance, and air leakage where reported. Frame material alone or the number of moving sashes does not substitute for these ratings. Match glazing to climate, orientation, shading, and code.
Measure the rough opening and determine whether the project is an insert replacement or full-frame installation. Full-frame work can reveal and correct flashing, sill, and water-management defects that an insert leaves in place. Installation quality and integration with the weather barrier are central to leak performance.
For a bedroom, confirm the exact unit meets local emergency escape and rescue opening requirements; a catalog size is not proof of the required clear opening. Choose single-hung when one sash meets ventilation and access needs and the simpler mechanism is attractive. Choose double-hung when upper-sash ventilation or interior cleaning access has real value. For repair symptoms, see a sash that is hard to open .