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A Steam Heat Primer by Dan Holohan (Podcast)

By Bryan Orr

In today's podcast episode, Bryan gives an audio recording of the legendary Dan Holohan's article, “A Steam Heat Primer.”

Read that article HERE.

Check out more about Dan's work at heatinghelp.com.

If you have an iPhone, subscribe to the podcast HERE, and if you have an Android phone, subscribe HERE.

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Author:

Bryan Orr

Company: HVAC School

Position: Founder

Check out our most recent video

How to Evacuate an AC system, Full Vacuum Procedure

Our latest Podcast

HVAC School – For Techs, By Techs

Real training for HVAC ( Heating, Ventilation, Air Conditioning and Refrigeration) Technicians. Including recorded tech training, interviews, diagnostics and general conversations about the trade.

In this long-awaited live episode of HVAC School, host Bryan Orr reunites with three industry veterans — Jim Bergmann of measureQuick, Roman Baugh (Kalos), and Andrew Greaves of NAVAC — to tackle one of the most pressing and underaddressed challenges in modern HVAC: performing refrigerant recovery and system evacuation in extreme cold-weather conditions. The conversation was sparked by a real-world observation from technician Chris Hughes, who relocated from Louisiana to Minnesota and quickly discovered just how different — and difficult — cold-climate HVAC work can be. What follows is an honest, science-heavy, and often humorous deep dive into a problem the industry has largely ignored.

The episode centers on the growing prevalence of cold-climate heat pumps, especially inverter-driven systems capable of operating at extremely low outdoor temperatures. As these systems become the primary heating source in cold regions, technicians are increasingly being called to make repairs — and perform evacuations — in sub-zero conditions. The group walks through why this is such a challenge, examining the fundamental physics that make pulling a proper vacuum nearly impossible once temperatures drop below 40°F. The conversation draws heavily from refrigeration science principles that, as Jim Bergmann bluntly points out, were largely left out of HVAC trade education over the past several decades.

One of the most compelling moments of the episode is Andrew Greaves’ introduction of the “heat provocation test,” a term he coins on the spot to describe a technique for verifying whether moisture has truly been removed from a system by observing micron gauge behavior after applying external heat to cold-soaked components. This sparks a rich debate between Jim and Andrew about where moisture actually concentrates in a system — in the line set vs. the outdoor unit — and whether heat can realistically reach those areas in a real-world installation. The panel ultimately agrees that heat is the only viable tool when you absolutely must complete a job in cold conditions, but that prevention and scheduling remain the gold standard.

The episode closes with a fascinating dive into the phase diagram of water, specifically the concept of the “triple point” and how it governs moisture behavior at low pressures. Andrew uses a whiteboard diagram to explain why, below 4,500 microns, moisture can only exist as vapor or solid — not liquid — and why that makes sublimation the only removal pathway when heat is absent. Jim adds nuance by describing the self-refrigerating cycle that occurs during deep vacuum pulls, a phenomenon that makes the problem progressively worse the deeper you pull without adding heat. The group wraps up with practical field takeaways and a promise to revisit the topic, including the potential role of nitrogen purging and triple-evacuation techniques in cold-weather scenarios.

Topics Covered

The rise of cold-climate heat pumps and why they demand refrigerant work during cold seasons
Why evacuation becomes extremely difficult — or impossible — below 40°F ambient temperature
The physics of moisture removal: heat energy, vapor pressure, and molecular movement
Jim Bergmann’s real-world demonstration pulling a vacuum to 135 microns on a wet system and still failing the decay test
Andrew Greaves’ “heat provocation test” — using external heat sources to verify dryness after evacuation
The debate over where moisture concentrates: outdoor unit vs. line set
Why mini-split manufacturers don’t allow permanent desiccant dryers — and workarounds using temporary bypass configurations
VRF systems and how shell dryers can be temporarily added and then removed post-evacuation
The self-refrigerating cycle: how pulling a vacuum on ice makes the system progressively colder and more resistant to drying
Phase diagram of water: the triple point (~4,580 microns) and why liquid water becomes unstable below it
Why sublimation is the only moisture removal pathway below the triple point
Gibbs free energy and its role in determining which phase (solid, liquid, vapor) a substance will occupy
Hot nitrogen purging as a method for carrying moisture out of open line sets
Push-pull recovery technique to maximize refrigerant removal in cold conditions
The challenge of vapor recovery in cold weather — leaving multiple pounds of refrigerant behind
Practical field solutions: insulated tarps, portable propane heaters, belly band heaters, heat guns
Dry ice cold-trap brainstorm as a creative moisture capture method
The dual-fuel argument: why Jim advocates for backup heating as the real long-term solution
How rapid industry growth in the mid-20th century led to mechanics being trained instead of engineers, losing foundational science in the process
Why this topic matters more now than ever as cold-climate compression refrigeration becomes mainstream