The short answer
Single-hung windows commonly have a movable lower sash and fixed upper sash; double-hung windows commonly allow both sashes to move. Compare ventilation control, cleaning access, hardware, clear opening, screen configuration, exact ratings, and the quoted product, not the style name alone.
| Compare | Single hung | Double hung |
|---|---|---|
| Upper sash | Commonly fixed | Commonly operable |
| Lower sash | Operable | Operable |
Sources
Sources
- Window Types and Technologies — U.S. Department of Energy
- Window Energy Performance Ratings — National Fenestration Rating Council