Episode quotes:

"Below about 0.4 microns, many low-cost PM sensors are basically guessing—right where wildfire smoke and aerosols live." — Sissi Liu

"Electrostatic filters can look great at first—and then fall off a cliff in smoke. Pressure drop won't warn you." — Sissi Liu

"Science is a way of thinking much more than it is a body of knowledge." — Carl Sagan

Eric digs into the "fresh air" myth with Sissi Liu, CEO/co-founder of Metalmark Innovations and active ASHRAE committee member. Sissi explains why "outdoor = fresh" is context-dependent—urban pollution, agricultural activity, and especially wildfire smoke can make outdoor air worse than indoor air. Because air quality is dynamic, she pushes for comparing indoor and outdoor conditions in real time and ventilating intelligently, with attention to the energy cost of conditioning outside air.

They then get nerdy on sensors and filters. Many low-cost PM2.5 laser-scattering sensors struggle below ~0.4 µm and can misread certain particle types (e.g., dark/black carbon), which matters because smoke and pathogen-carrying aerosols often live in the ~0.1–0.3 µm range. On filtration, Sissi contrasts mechanical vs. electrostatically charged media: electrostatic filters start efficiently with low pressure drop but can lose effectiveness within hours in smoke events. In contrast, mechanical media hold up better (though at higher pressure). She highlights ASHRAE 52.2 Appendix J (loaded efficiency) and argues that standards—along with reporting practices—must evolve for wildfire realities.

• "Fresh air" is conditional: check outdoor AQ (and indoor) before cranking up ventilation.
  
  

• IAQ is dynamic; test and compare locally rather than assuming static conditions.
  
  

• Consumer PM sensors can under-count the tiniest and darkest particles; treat data with caveats.
  
  

• Wildfire smoke clusters in the most-penetrating particle size (~0.1–0.3 µm) for many filters.
  
  

• Electrostatic filters may degrade fast in smoke; pressure drop alone won't reveal failure.
  
  

• ASHRAE standards (e.g., 52.2 Appendix J, SGPC-44) are evolving—industry needs to catch up.

Sissi's LinkedIn: https://www.linkedin.com/in/liusissi/

Metalmark website: https://metalmark.xyz/

This episode was recorded in October 2025.

Eric Kaiser sits down with Haley Harlow and Al Mitchell from PHIUS (Passive House Institute US) to explore Revive 2024, a groundbreaking new retrofit standard focused on thermal resilience and healthier, safer existing buildings. Haley shares her path from Pennsylvania College of Technology to her current role managing building certifications at PHIUS. At the same time, Al recounts his journey from aspiring car engineer to building scientist, drawn to the elegant complexity of whole-building systems.

Together, they unpack how Revive differs from traditional PHIUS new-construction standards. Instead of focusing on heating and cooling load targets, Revive emphasizes thermal resilience—a building's ability to remain habitable for up to a week during power outages or extreme weather. They also discuss ReviveCalc, PHIUS's new software tool for analyzing retrofit scenarios, allowing designers to test various upgrade packages, balance cost and performance, and phase improvements over time. The tool incorporates lifecycle cost analysis, dynamic energy modeling, and resilience metrics, making advanced design decisions more accessible to real-world projects.

Both guests share their excitement about addressing the massive stock of underperforming existing buildings. Haley connects it to her own experience growing up in energy-intensive apartments, while Al reflects on how to use today's computing power better to design resilient, efficient homes. They close with a shared message: retrofitting our current buildings is not only possible, it's essential for the future of sustainability, comfort, and community resilience.

• PHIUS Revive 2024 focuses on retrofits, bringing resilience and energy equity to the existing building stock.
  
  

• Thermal resilience replaces traditional load metrics, ensuring buildings remain habitable during grid or system failures.
  
  

• ReviveCalc helps users model envelope and mechanical upgrades, estimate lifecycle costs, and optimize phase-by-phase improvements.
  
  

• The program aligns with ASHRAE Guideline 0.2 for commissioning and integrates EPA's Energy Savings Plus Health framework.
  
  

• Air sealing remains the top "bang for the buck" retrofit measure for both comfort and energy savings.
  
  

• CPHC certification (Certified PHIUS Consultant) is open to anyone—no degree required.
  
  

• The Revive approach balances performance, cost, and practicality for real-world projects.

Haley's LinkedIn: https://www.linkedin.com/in/haley-harlow-3965b41b5

Al's LinkedIn: https://www.linkedin.com/in/al-mitchell-bb74827b/

Info on Phius Revive 2024: https://www.phius.org/phius-revive-2024

This episode was recorded in October 2025.

Quotes by Brantley:

"Most moisture problems are a three-way dance—envelope, mechanicals, and the occupants."

"Skim the light, don't blast it. The right flashlight technique makes the invisible visible."

"If you only understand one piece of the system, you're solving 1/3 of the problem."

Indoor environmental specialist Brantley May joins the show to unpack how he investigates moisture, mold, and air-quality problems through building forensics. Starting as a mold remediator in his family business, Brantley shifted to assessment work and now runs national investigations that pinpoint root causes—from envelope leaks and interstitial space connections to mechanical design and operation issues. He explains the value of "flashlight technique" (skimming light across surfaces to reveal early hyaline mold) and why good eyes, a light, and critical thinking are still the most important tools in the bag.

Brantley walks through his toolkit—manometers, blower doors, pressure pans, thermal imagers, moisture meters, anemometers/flow hoods, data loggers, and even a backup sling psychrometer—plus his new favorite screening instrument, the InstaScope, which provides real-time readings on particulates, mold/pollen, bacteria/virus, VOCs, and CO₂. Investigations culminate in a report and protocols for the envelope, mechanicals, and remediation, often requiring tight coordination across multiple trades. He stresses pre-drywall inspections, "red-pen" continuous air/thermal barrier checks, and long-term monitoring to verify theories—especially on complex modern designs where vented attics and interstitial spaces end up unintentionally connected.

A major theme: cross-disciplinary literacy. Most condensation/humidity problems stem from three interacting factors—envelope failure, mechanical failure, and occupant behavior—so HVAC pros must understand building science, and envelope pros must understand HVAC. Brantley shares how training (BPI, IICRC), mentorship, microscopy work (McCrone/Ochsner), and relentless curiosity shaped his practice. Watch for him at industry events (HVACR School Symposium, Build Show)—maybe even submitting a short BryX talk next time.

Brantley's LinkedIn: https://www.linkedin.com/in/brantley-may-b3988283/

His company: EnviroHealth.co

His Instagram: https://www.instagram.com/brantley.iaq/

McRone Institute: https://mccroneinstitute.org/

Instascope: https://www.instascopeair.com/

Institute of Inspection Cleaning and Restoration Certification: https://iicrc.org/

Building Performance Institute: https://www.bpi.org/

Building Science Summer Camp:

https://buildingscience.com/events/twenty-fifth-annual-westford-symposium-building-science

National Home Performance Conference: https://building-performance.org/events/national/

This episode was recorded in October 2025.