Passive House windows

If you are designing to Passivhaus, the window is usually the hardest component to satisfy. This page states the criteria, gives our certified figures converted into the units the standard uses, and is explicit about the one thing we cannot claim.

Key facts

We are NOT a PHI-certified component supplier: We do not hold Passive House Institute component certification — Source: Stated plainly rather than implied — see below
Passivhaus window criterion, cool-temperate climate: Installed U-factor ≤ 0.15 Btu/h·ft²·°F (the standard states it as 0.85 W/(m²·K)) — Source: Passive House Institute component criteria — a metric standard, converted here
Our best certified whole-window U-factor: 0.14 Btu/h·ft²·°F — Source: NFRC CPD SHN-M-24, UPVC Fixed Window
Best thermally broken aluminum: 0.16 Btu/h·ft²·°F — Source: NFRC CPD SHN-M-21
What NFRC certifies: The whole window in a standard test size — not the installed assembly with its thermal bridges
The gap that matters: Passivhaus rates the INSTALLED unit including the psi-value of the fixing detail; an NFRC rating does not cover installation

What we cannot claim, stated first

We do not hold Passive House Institute component certification. If your project requires a PHI-certified window from the certified component database, we are not currently that supplier, and no amount of good U-factor data changes it.

We are putting that at the top rather than at the bottom because a specifier who discovers it at plan check has been wasted, and because everything below is more useful once it is out of the way.

What the standard actually asks for

For a cool-temperate climate, the Passive House Institute component criteria set an installed window U-factor of 0.15 Btu/h·ft²·°F or better, with glazing at 0.12 or better, plus criteria on glazing g-value and on the thermal bridge at the installation joint. PHI writes those as 0.85 and 0.70 W/(m²·K) — it is a European standard — so if you are cross-checking against its own documentation, that is where the metric figures come from.

The word doing the work is installed. PHI rates the window as built into the wall, including the psi-value of the fixing detail. An NFRC rating is a whole-window rating at a standard test size and does not describe your installation — the two are not interchangeable, and a window that meets the number in one system has not automatically met it in the other.

What we can evidence

We hold 44 NFRC-certified product lines across 2,485 rated configurations. The best certified whole-window U-factor is 0.14 Btu/h·ft²·°F on a UPVC fixed window; the best thermally broken aluminum line certifies 0.16. Both are comfortably inside the 0.15 criterion at the glazing level, before installation effects are counted.

On the U-value criterion alone, that best UPVC line is in the right territory before installation effects are counted. On a low-energy or net-zero project that is not being formally PHI-certified, those are real, third-party-verifiable numbers you can specify against. Ask for the CPD number and check it in the public directory yourself.

PHI criterion (cool-temperate, installed)	≤ 0.15 Btu/h·ft²·°F (0.85 W/(m²·K) as the standard writes it)
Our best certified whole-window U	0.14 Btu/h·ft²·°F — CPD SHN-M-24
Best thermally broken aluminum	0.16 Btu/h·ft²·°F — CPD SHN-M-21
PHI component certification	Not held

Products this applies to

Every product below is in the live catalogue with its own specification table.

UPVC Fixed Window UPVC Casement Window Signature Slimline Tilt & Turn Essential Tilt & Turn

Questions we are actually asked

Are your windows Passive House certified?

No. We do not hold Passive House Institute component certification. Our performance data is NFRC-certified, which is third-party verified and publicly checkable, but it is a different certification scheme and does not substitute for PHI component certification if your project requires one.

Can I use your windows on a low-energy or net-zero project?

Yes, provided the project is not being formally certified against the PHI component database. Our best certified whole-window U-factor is 0.14 Btu/h·ft²·°F. Ask us for the CPD number covering the exact configuration and verify it yourself before specifying.

Why do your U-factors look so different from European datasheets?

Units. NFRC ratings are in Btu/h·ft²·°F; European datasheets are in W/(m²·K). Multiply the US figure by 5.678 to convert. A number like 0.14 is excellent in US units and would be nonsensical read as metric.