The U-value is a coefficient that measures how much heat passes through one square metre of window per one degree of temperature difference. The unit is W/m²K (watts per square metre per kelvin). The lower the value, the better the window's thermal insulation.

Uf, Ug, and Uw — what's the difference?

• Uf (frame) — U-value of the profile frame only
• Ug (glass) — U-value of the insulating glass unit only
• Uw (window) — U-value of the assembled window as a whole (the number that matters)

In product specifications, look at Uw — that is the real performance figure.

What counts as a good Uw?

What is recommended for the Uzbekistan climate?

For Tashkent and the wider Central Asian climate, Uw ≤ 1.0 W/m²K is a sensible standard. It cuts winter heating costs by 25–35 % and prevents condensation. Engelberg's Termo 98 (Uw ~0.8) exceeds this benchmark.

What U-value affects

• Utility bills: moving from Uw 1.4 to 0.8 cuts annual heating costs by 20–30 %
• Comfort: a low-U glass surface stays warmer — sitting next to the window feels less cold
• Condensation: high-U windows "sweat" in winter, which leads to mould
• Environment: lower U means fewer CO₂ emissions

How to check

Ask the supplier for the Uw value in writing (not just Uf or Ug). Reputable manufacturers list it on the technical data sheet, verified by a certification body such as TÜV Rheinland.