Buyer tools · Thermal
U-value calculator. Pass the energy code before you specify.
Size the unit, choose the glass, spacer and profile depth, and see the whole-window Uw per EN ISO 10077-1 update as you type — with the U-factor in Btu, the g-value, the condensation risk at your design temperature and the code limits it meets.
Configuration
Uw1.37W/m²K
- U-factor
- 0.241 Btu/h·ft²·°F
- Solar factor gw
- 0.41 g 0.60
Where the heat goes
- Glass55%
- Frame32%
- Glass edge13%
- Frame fraction
- 31%
- Glass area
- 1.25 m²
- Unit area
- 1.82 m²
- Perimeter
- 5.42 m
Indicative EN ISO 10077-1 calculation with tabulated Uf, Ug and ψ values. Verify with your energy consultant or certifier; the declared Uw on the CE / UKCA declaration of performance is the value of record.
Code limits Indicative
6/12 · Uw 1.37
- Passive House componentPHI · ≤ 0.80 W/m²KFail
- ENERGY STAR NorthernUS · ≤ 1.25 W/m²K · U ≤ 0.22 BtuFail
- Part L 2021 notional (new build)UK · ≤ 1.20 W/m²KFail
- ENERGY STAR CanadaCA · ≤ 1.22 W/m²KFail
- GEG (Germany)DE · ≤ 1.30 W/m²KFail
- MaPrimeRénov' (France)FR · ≤ 1.30 W/m²KFail
- Part L 2021 replacementUK · ≤ 1.40 W/m²KPass
- ENERGY STAR North-CentralUS · ≤ 1.42 W/m²K · U ≤ 0.25 BtuPass
- Part L 2021 limitingUK · ≤ 1.60 W/m²KPass
- CTE DB-HE zone D/E (Spain)ES · ≤ 1.80 W/m²KPass
- ENERGY STAR SouthernUS · ≤ 1.82 W/m²K · U ≤ 0.32 BtuPass
- Dubai Green Building RegulationsAE · ≤ 1.90 W/m²KPass
Limits are indicative maximum Uw values for windows in new or replacement work; national rules vary with building type, compliance route and reference size. ENERGY STAR and NFRC rate U-factor at NFRC sizes and boundary conditions, so an EN ISO 10077 value is only a first check.
Condensation risk
BorderlineTi 20 °C · RH 50% · Te -10 °C
- Centre of glass
- 15.7 °C
- Glass edge
- 9.8 °C
- Frame (inside)
- 14.5 °C
- Dew point
- 9.3 °C
The coldest surface is within 3 K of the dew point. Upgrade the spacer or profile depth, or ask for a 2-D THERM/Flixo check.
02 — Buyer FAQ
U-value questions from specifiers
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