What is a double-hung window?

What this means for your home project

1. Record whether the upper and lower sashes move; include their opening operation in your window request. Source: National Fenestration Rating Council — Efficient Windows Collaborative, read 2026-11-05.
2. For historic windows, photograph each unit and prepare a parts-and-condition list so the repair assessment can address individual windows. Source: National Park Service, read 2026-11-05.
3. Request frame-to-opening insulation in the written installation scope; ask the installer to identify how that gap will be insulated. Source: U.S. Environmental Protection Agency — ENERGY STAR, read 2026-11-05.
4. Request the selected window’s manufacturer installation instructions with the proposal so you have a document to compare with the planned work. Source: U.S. Environmental Protection Agency — ENERGY STAR, read 2026-11-05.

What is a double-hung window vs single-hung?

Use NFRC’s descriptions (read 2026-11-05) to identify which sash moves; NYC’s architectural glossary supplies the vertical-track terminology. “Single-hung windows have two sashes: a fixed one in the top half of the window, and a sliding one on the bottom that moves up or down.” (source) “Double-hung windows have two sliding sashes.” (source) “The top sash can be lowered and the bottom sash can be raised, providing the choice of which parts of a window to leave open.” (source) “Double hung: A type of window with two sash, each sliding on a vertical track.” (source)

Are double-hung windows energy efficient?

Use DOE’s rating explanations (read 2026-11-05) to evaluate a double-hung product’s insulation and air leakage when comparing window labels. “U-Factor measures the rate of heat transfer and tells you how well the window insulates.” (source) “U-factor values generally range from 0.15 to 1.1 and are measured in Btu/h•ft²•°F.” (source) “The lower the U-factor, the better the window insulates.” (source) “Air Leakage (AL) measures the rate at which air passes through joints in a closed window.” (source) “AL is measured in cubic feet of air passing through one square foot of window area per minute.” (source) “The lower the AL value, the less air leaks through the window.” (source)

Can double-hung windows be repaired?

For historic double-hung windows, NPS guidance (read 2026-11-05) helps frame a condition assessment before deciding which parts need replacement. “Historic windows and doors can often be repaired or upgraded to improve energy efficiency and occupant satisfaction.” (source) “Conducting a window inspection is a good way to assess the overall condition of your windows and to determine whether repair or replacement is the better alternative.” (source) “But, if a large number of new parts are required, then it may be appropriate to consider investing in a good, matching replacement window.” (source)

What factors affect the cost of double-hung windows?

ENERGY STAR distinguishes product choice from installation labor; NPS identifies repair complexity as another scope consideration (both read 2026-11-05). “ENERGY STAR certified windows, doors and skylights may cost more than non-certified products, but the labor involved should be comparable for both.” (source) “More extensive repairs may require a professional.” (source)

What should I look for when I am buying a double-hung window?

Use DOE’s ENERGY STAR specification 7.0 guidance (read 2026-11-05) to compare climate suitability and obtain installation instructions before ordering. “Figure 4 shows the ENERGY STAR Program Requirements for Residential Windows and Skylights, Version 7.0.” (source) “This version took effect on October 23, 2023.” (source) “Look for ENERGY STAR-labeled products that meet or exceed the criteria for your climate zone.” (source) “ENERGY STAR certified windows, doors, and skylights are required to have installation instructions packaged with the product or readily available online.” (source) “Some manufacturers will void your warranty if you do not follow manufacturer installation instructions.” (source)

Sources

• Architectural glossary — New York City Landmarks Preservation Commission; read 2026-11-05.
• Window Types — National Fenestration Rating Council — Efficient Windows Collaborative; read 2026-11-05.
• Weatherization of Historic Buildings: Repair and Upgrade Windows and Doors — National Park Service; read 2026-11-05.
• High-Performance (ENERGY STAR) Windows — U.S. Department of Energy — Building America Solution Center; read 2026-11-05.
• Residential Windows, Doors, & Skylights — U.S. Environmental Protection Agency — ENERGY STAR; read 2026-11-05.