Information · Passive House & Phius
Passive House & Phius
What is a Passive House?
A Passive House is a building that needs very little energy for heating and cooling, because its envelope does most of the work. Five principles get it there: continuous insulation, an airtight envelope, thermal-bridge-free detailing, high-performance windows and doors, and balanced ventilation with heat or energy recovery. The result is a building with steady temperatures, fresh air and no cold spots, that uses a fraction of the energy of a code-built one.
There are two certifying organizations in North America, and they are often confused.
Passive House Institute (PHI)
The Passive House Institute in Darmstadt, Germany, founded by Dr. Wolfgang Feist, created the Passive House standard; the first Passive House was built in Darmstadt in 1991. PHI’s criteria are the same everywhere in the world, and buildings are modeled in PHI’s Passive House Planning Package (PHPP).
- Heating demand of no more than 15 kWh/m² per year, or a peak heating load of no more than 10 W/m².
- Airtightness of no more than 0.6 air changes per hour at 50 pascals (n50).
- Renewable primary energy limits, with Classic, Plus and Premium classes for buildings that also produce renewable energy.
Phius
Phius, founded in the United States in 2007 and based in Chicago, runs the Phius CORE and Phius ZERO standards. Instead of one set of numbers for the world, Phius sets targets for each location, based on its climate and on what is cost-effective there. Buildings are modeled in WUFI Passive, and certification includes on-site verification by a Phius verifier or rater.
- Phius CORE sets climate-specific limits on heating and cooling demand and peak loads, an airtightness limit of 0.060 cfm per square foot of envelope at 50 pascals, and source-energy limits.
- Phius ZERO adds renewable energy to reach net zero source energy.
- Phius CORE Prescriptive offers a simpler, checklist-based path for some projects.
PHI and Phius compared
| Passive House Institute (PHI) | Phius | |
|---|---|---|
| Based in | Darmstadt, Germany | Chicago, United States |
| Targets | The same worldwide | Set for each location’s climate and costs |
| Modeling tool | PHPP | WUFI Passive |
| Airtightness | n50 ≤ 0.6 ACH | ≤ 0.060 cfm50 per ft² of envelope |
| Professionals | Certified Passive House Designers and Consultants | Certified Passive House Consultants (CPHC), verifiers and raters |
| Window ratings | EN ISO 10077, PHI component certification | Phius window program, by NFRC or EN methods |
Both produce excellent buildings. Many U.S. teams choose Phius for its climate-specific targets and its links to U.S. programs; others choose PHI for its single international standard. Some energy codes and funding programs accept either: Massachusetts’ Specialized Opt-in Code, adopted by dozens of municipalities, requires larger multifamily buildings to meet Passive House standards. To see how Phius and PHI window data relate to NFRC and CSA ratings, and what a building department will ask for, see Which Rating Applies?
What Passive House asks of a window
In a Passive House, windows are usually the weakest part of the envelope, so both organizations set high bars.
PHI certified components. PHI certifies windows for seven climate zones, from arctic to very hot. For the cool, temperate zone, a window must reach Uw ≤ 0.80 W/m²K, and no more than 0.85 once installed, with an interior surface temperature factor fRsi of at least 0.70 to prevent cold surfaces and condensation. Certified windows are also given an efficiency class, from phA+ (best) down to phE, based on heat lost through the frame and glass edge.
Phius certified windows. Phius certifies windows by NFRC methods (its Blue Path) or EN methods (its Orange Path), and recommends whole-window values for each U.S. climate zone:
| IECC climate zone | Max U-factor, Btu/h·ft²·°F | Max U, W/m²K | Max SHGC |
|---|---|---|---|
| 8 | 0.11 | 0.62 | – |
| 7 | 0.12 | 0.68 | – |
| 6 | 0.13 | 0.74 | – |
| 5A, 5B | 0.16 | 0.91 | – |
| 4A, 4B | 0.19 | 1.08 | 0.40 |
| 4C, 5C | 0.24 | 1.36 | – |
| 3A | 0.23 | 1.31 | 0.25 |
| 3B | 0.29 | 1.65 | 0.25 |
| 3C | 0.29 | 1.65 | 0.30 |
| 0, 1, 2 | 0.29 | 1.65 | 0.25 |
Phius values from the Phius Window and Door Certification Program summary, v1.2 (April 2026). They are recommendations; Phius project certification rules govern.
Where GlasFëns fits
Our GR85 dual action window is a Certified Passive House Component, certified by the Passive House Institute for both the cold and the cool, temperate climate zones, in the highest efficiency class, phA, with certified installation values for three wall types. With ZERO 04 hybrid vacuum glass, our GR85 fixed and dual action windows calculate at 0.085 and 0.093 Btu/h·ft²·°F, below even the climate zone 8 recommendation. See the performance page for the certificate values and every system, and ask us for PHPP and WUFI Passive inputs.