How to choose an energy-efficient window

How to choose an energy-efficient window: which profile and glass-unit parameters define thermal insulation, and how much replacing old windows cuts heat loss. The key benchmark is the heat-transfer resistance coefficient.

The video compares three tiers of energy-efficient windows, from a standard build to solutions for passive houses.

What the video shows

• a home's heat-loss breakdown: leaky windows 25–47%, walls 18–25%, roof 11–18%, ventilation 10–15%, floors and basement 3–9%;


• a window's efficiency is judged by its heat-transfer resistance coefficient — at least 0.75;


• "standard": 5-chamber 70 mm profile (e.g. REHAU Euro-Design 70), steel reinforcement from 1.5 mm, 40 mm double-chamber insulating glass unit, argon, low-e coating — about 2.5x warmer than an old timber window;


• "premium": 6–7-chamber 80 mm profile (e.g. REHAU Synego), glass unit up to 44 mm, argon, two low-e panes — about 3x warmer;


• for passive houses: 6-chamber 86 mm profile (e.g. REHAU Geneo), often without steel reinforcement, glass unit up to 52 mm, krypton — about 5x warmer.

Whatever the window class, its thermal performance also depends on correct installation with vapour and waterproofing sealing.