As you navigate the world of Passive House in the US, it’s not unusual to find yourself asking what the difference is between the Passive House Institute (PHI) and Phius. While there is no simple explanation, we can look at the approaches, metrics, and results to get a better sense of where each stands. We hope this collection of brief descriptions, charts, and links gives you a better understanding of how the two programs may related to each other and your work. – PHN

Moving Markets or Moving Performance

PHI has applied Passive House understanding to new uses, typologies, and climates while maintaining the most robust requirements, reinforcing its logic, and pushing the industry to move toward normalizing high-quality everywhere. Phius has instead lowered standards on window and ventilation units, and weakened the logic of high-quality, to move toward the American market. We appreciate that markets resist change, but moving quickly to accommodate industry norms instead of challenging them shortchanges the potential for market transformation. This is exemplified in PHI’s Component Database and PHN’s growing Manufacturer’s Directory, where a growing number of manufacturers and suppliers can be found.

Simplification or Complication

PHI offers a focused approach to the process of making exceptionally high-performing buildings, as exemplified by the “5 Principles” and specific energy targets that frame project development efforts. It allows for—but does not require—integration with other certification systems (e.g., LEED, DOE ZERH, and WELL). Phius incorporates multiple U.S. programs as mandatory co-requisites (e.g., EPA Energy Star, EPA airPLUS, and DOE ZERH), which can distract from the critical benchmarks.

The Passive House Network views PHI’s laser-like focus on performance drivers as a great gift to project teams, allowing them to layer in additional goals at their discretion.

Global or National

PHI is the scientific research institute that developed Passive House based on international scientific standards, and focuses on its development worldwide. PHI is led by a team of physicists with over 30 years of global technical leadership and scientific research, producing wide-ranging resources. Phius derived its approach from PHI, but changed the metrics and norms to accommodate the existing American industry.

The Passive House Network (PHN) is part of PHI’s global effort, learning and working with people on buildings across borders, climates, and cultures.

What About Retrofits

PHI launched the EnerPHit retrofit certification standard to address the special needs of existing buildings—including orientation, existing structural thermal bridges, air sealing difficulty, interior insulation, and historic preservation requirements and more — while maintaining the high quality and durable results expected from a Passive House building. EnerPHit is a straightforward and flexible approach that has a track record of results. Phius launched its retrofit standard in 2024 and largely dispenses with Passive House logic, instead focusing on the ability to shelter in place. It is less a retrofit version of Passive House than another animal altogether.

Transparency or Black Box

PHI provides a relatively simple and transparent calculating tool called Passive House Planning Package (PHPP). PHPP is robust enough to provide predictable outcomes. PHPP’s calculated energy balance, with instantaneous feedback, is core to the effort’s DNA. Phius uses the proprietary WUFI Passive program, a more complex calculation engine where the calculations are not openly accessible or transparent.

Calculated or Prescriptive

PHI simplifies the optimization process for single-family homes with the easyPH PHPP, which maintains the core Passive House approach of calculating the energy balance. Phius, however, in an attempt to simplify single-family homes, swaps the calculated energy balance for a prescriptive method, taking a significant step away from Passive House logic.

How do Project Costs Compare

There are a multitude of possible cost drivers in construction. Consequently, Passive House need not be a prime driver of overall project cost. Phius’ general admission of lower quality windows, ventilation units, and thermal bridging mitigation can lead to lower component costs; however, mandating additional EPA and DOE certification requirements add costs.

A range of “extra” costs to building is driven by the team’s experience, and how realistic the baseline cost is, not whether the project is PHI or Phius. See the PHN report, Is Cost the Barrier to Passive House Performance?

What are the Performance Outcomes?

Energy Standards aren’t easy to compare; however, there is an excellent study completed by Emu Passive that looks at PHI, Phius, compares them across a variety of metrics, and presents comprehensive results and analysis. The bottom line? PHI’s Low Energy Building (PHI-LEB) standard performs similarly with Phius Core, while PHI’s Classic, Plus, and Premium standards outperform Phius Core.

To meet the Massachusetts Specialized Code, projects can be certified to PHI-LEB, Classic, Plus, and Premium standards as well as Phius Core and Zero.