What U-value means for your climate
Window brochures, including ours, list U-values such as 1.4, 0.95, and 0.79 W/m²K. The figure describes thermal transmittance, but it must be read together with the component being measured and the stated test conditions.
What the number measures
U-value measures how much heat passes through one square meter of a building element for each degree of temperature difference between inside and outside. It is expressed in watts per square meter per kelvin (W/m²K). A lower value indicates better insulation. Under the same area and temperature conditions, a window with U = 1.0 transfers half as much heat as one with U = 2.0.
Uf, Ug, and Uw
Product information may list three related U-values. They describe different parts of the assembly and should be compared on the same basis:
- Uf: the thermal transmittance of the frame, including the aluminum profiles and thermal breaks.
- Ug: the thermal transmittance of the glazing unit, determined by the panes, cavity dimensions, coatings, and gas fill.
- Uw: the thermal transmittance of the complete window, combining the frame and glazing at the stated reference size.
A low Ug value does not by itself describe the performance of the complete window. For a direct comparison between window assemblies, compare Uw with Uw under equivalent reference conditions.
How low do you actually need to go?
The appropriate U-value depends on climate, building use, glazing area, orientation, and energy targets. As a practical guide:
- Mild coastal climates, where winter temperatures rarely fall below freezing: Uw around 1.8–2.5 W/m²K is usually sufficient. M9660 can be specified within this range without selecting a higher-insulation system than the project requires.
- Continental climates with cold winters, including Tbilisi, much of Georgia, and the central USA: target Uw around 1.0–1.5. S67 and S700 can be configured within this range.
- Cold or mountain climates, or projects with very low energy targets: Uw under 1.0. Passive House-grade systems such as S91 (Uw 0.79) are intended for this range.
U-value isn't the whole story
Other properties also affect year-round performance. The g-factor describes how much solar energy passes through the glazing; the appropriate value depends on climate, orientation, shading, and glazing area. Glass thickness and build-up determine structural capacity, safety, and sound insulation, particularly for large panes.
Argo specifies U-value, g-factor, glass build-up, and thickness together, based on the orientation, dimensions, safety requirements, and wind exposure of each opening. Send us your project details if you need a project-specific calculation.