Window Thermal Insulation and Sash Impact

When discussing window thermal insulation, attention tends to focus only on glass, but sash (glass frame) also greatly affects window thermal insulation. The proportion occupied by sash in windows appears small compared to glass, but aluminum, commonly used as sash material, has the property of "very easily conducting heat." Its thermal conductivity is about 200 times※1 that of glass, so even if the visual proportion in windows appears small, the impact on thermal insulation cannot be ignored.

For example, for a 1m × 1m window with sash visible dimensions of 50mm all around, the area ratio of glass to sash is

Glass : Sash ≒ 4 (0.81m²) : 1 (0.19m²)

showing that sash has a surprisingly high area ratio, different from visual impression.

Therefore, no matter how high the thermal insulation of the glass, if sash without thermal insulation consideration is used, the entire window may not achieve the expected thermal insulation effect. Similarly, when using insulating glass units to suppress condensation, if combined with sash with low thermal insulation, condensation on glass can be suppressed but sash will condense. To prevent window condensation, it is necessary to select sash with high thermal insulation in addition to glass.