PHIUS Certified Data for Windows program online

Graham Wright, who heads up the PHIUS Certified Data for Windows program, joins us today to provide clarifications on some key features of the program. And to clear up some misinformation.

I get and see online a lot of questions about the PHIUS Certified Data for Windows program, and how it differs from PHI’s Euro-centric program. Apologies—it’s clear that we haven’t communicated the program as well as we should have—but we are catching up to ourselves.

I’m happy to report that we’ve got data and climate recommendations for a nice range of windows online here.

The table lists products, climate zone recommendations, full data certificates and supporting THERM files.

There are a lot more coming—and we’ll be converting this static table to an online database soon.

For manufacturers and suppliers, we invite you to download a detailed description of the certification process (with an application form), and the document is also available at the program overview page.

In the meantime, I hope to clear up misconceptions and concerns about the program:

I heard that the PHIUS Certified Data for Windows program doesn’t account for whole-window R-value. Is that correct?

In fact, the program does provide recommendations based on whole-window R-value, and all have the force of criteria as far as manufacturers are concerned. Also the program provides recommendations / criteria on solar heat gain coefficient.  (They vary by climate from about R-5 to R-9.)

Why doesn’t the program address surface temperature factor (“fRsi”)?

Eventually, it probably will – but on the list of important future program improvements for North America, it’s pretty far down the list, after data publication, NFRC harmonization, air-tightness-durability, and Canadian Energy Rating. That’s partly because fRsi isn’t pertinent to hot climates (and there’s a lot of hot climate zone in North America), and we decided to pay more attention to solar heat gain coefficient.

We cover the condensation / fRsi issue by providing the THERM files, which allow consultants to calculate it if they wish, and more precisely, with respect to the expected interior humidity conditions for their particular project and climate. (I made an ASHRAE 160 + ISO 13788 calculator for computing fRsi requirements climate- and project- specifically. We make it available during CPHC training, and if you email me at, I’ll be happy to send it to you.)

Moreover, both the fRsi criterion and the single-height bar on U-value (at about R-7) look to be legacies of the single-zone origin of PHI’s window program.

Setting that high bar at R-7 has certainly spurred innovation. But our multi-zone system does the same thing – people want to “level up” from zone 3 to 4 or from 4 to 5.  A single standard, when it comes to windows, fails to inform a shopper whether a window is appropriate for a passive house project because it’s overkill in some places and under kill in others.

It also hurts manufacturers—many of them mainstream producers of very affordable windows—who, right now, offer windows that will work well in mild climates. Designers, builders and clients should have those options.

Moreover, we find much to admire in the NFRC system and would like to get the best of both worlds. Funding for such harmonization work is being applied for.

Do we really need the PHIUS window program?


PHIUS’ window program is moving toward a critical goal: producing data in the format that passive house consultants need, and that enables direct comparison to windows rated by other EN-based outfits like PHI or say, IFT Rosenheim. Both window industry representatives and passive designers have told us this is critical if we want to energize the market. To be sure, the programs’ fundamentals are aligned, but the presentation and recommendation level is different in a number of ways. For example, PHIUS’ program is more fussy about solar heat gain and zone granularity. PHI’s is more fussy about horizontal / vertical.

At PHIUS we believe that passive house principles apply universally, but a single criterion does not. From their Greenbuild presentation, it was clear to me that PHI recognizes the need for climate-specific recommendations for components, including windows.  But as I understand it their window certification is still pass/fail at one level. PHIUS has moved more quickly on this front. Going forward, if you hear “this is a passive house window” people should know to ask:  for what climate?  Be wary of claims about passive house windows that don’t show any numbers or label or certificate, it might just be loose talk.

Why such a long name? Why not just PHIUS Certified Window, for example

We settled on the name with care. The AAMA or NFRC would say, you don’t have a “window certification program” unless you address air / water / structural issues. So PHIUS is not certifying windows (and neither does PHI by such lights).

We’re certifying certain data about windows, namely thermal performance, modeled. Hence, “PHIUS Certified Data for Window Performance Program.”

We did not include the term “passive house” because while designed with passive house in mind, the data—even for windows that don’t receive recommendations for passive application—will be extremely useful for designers.

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