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Tech Tips:

A good technician uses their senses before they use diagnostic tools. Is your suction line abnormally cold? Make sure the evaporator coil isn't frozen, and inspect for obvious airflow issues like a dirty filter or evaporator coil. Is your liquid line abnormally warm to the touch? It could be a dirty condenser, condensing fan issue, […]

Troubleshooting For HVAC/R – Gathering Data

This article is part 3 in a 5-part series by Senior Refrigeration and HVAC Technician Jeremy Smith. Let's start with step#1 in the flowchart: Gather data. This is why we spend money on those fancy digital manifolds, shiny electrical meters, and other gadgets, widgets, and doodads. It isn't to brag about them on Facebook; it's […]

Troubleshooting For HVAC/R – The Don’t List

This article is the second in a 5-part series by Senior Refrigeration and HVAC tech Jeremy Smith. The Ground rules I've spent some time thinking about troubleshooting and the processes and procedures that I use to find problems. Not the “why isn't my air-conditioner running?” problems, but the “Things just aren't quite right”-type problems—the really […]

The Troubleshooting Mindset

This article was written by Senior Refrigeration tech Jeremy Smith. Big thanks to Jeremy for his contributions to HVAC School and the tech community. Having spent many years in the trade and many years reading posts from techs on forums and social media, a big issue that I see is that troubleshooting is something of […]

Troubleshooting Advanced Systems

This article was written by Senior Refrigeration Tech Jeremy Smith. Before we get to it, I want to remind you that ALL of the tech tips are available in chronological order HERE, and you can sort through them alphabetically by selecting the letters and numbers above the tips. It's a great link to share with […]

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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 comprehensive episode, Bryan and Roman dive deep into one of the most challenging topics in modern HVAC: making VRF (Variable Refrigerant Flow) and ductless systems perform effectively in humid climates like Florida. The conversation tackles a common misconception that inverter-driven equipment automatically handles humidity well simply because it can “turn down.” Roman emphasizes that successful application of VRF technology in humid environments requires skilled professionals who understand building science, envelope integrity, and proper system sizing. The biggest takeaway? If you’re going to err on sizing, undersize rather than oversize – these systems will run longer and maintain better humidity control when properly sized.

The hosts explore the three critical factors for dehumidification: runtime, coil temperature, and surface condensation. They explain how traditional inverter systems were programmed for energy efficiency by allowing coils to warm up as they approached the set point, which unfortunately sacrifices latent capacity. Modern systems with active dehumidification capabilities use expansion valve control to “starve” the coil, lowering saturation temperature to around 35-37 degrees while extending runtime. Roman shares his personal experience with a 7,000 BTU unit serving his 700 square foot master bedroom suite, demonstrating how proper application and understanding of equipment capabilities can deliver excellent humidity control without oversizing.

The discussion takes a practical turn as Bryan presents a comprehensive troubleshooting checklist for humidity problems, starting with bulk water leaks and progressing through envelope integrity, duct sealing, equipment selection, and pressure balancing. They debunk common “solutions” that actually make problems worse, like adding attic insulation or solar attic fans without addressing root causes. The conversation reveals a counterintuitive truth: reducing sensible load through excessive insulation can worsen humidity problems by reducing equipment runtime. They explain why “active dehumidification” through overcooling isn’t true dehumidification, and why another solution – reheat – requires adding sensible heat back to spaces to maintain longer equipment runtime.

Topics Covered:

VRF and inverter sizing misconceptions – Why undersizing is often better than oversizing in humid climates
Three factors of dehumidification – Runtime, coil temperature, and surface condensation explained
Active dehumidification technology – How expansion valve control creates longer runtime and colder coils
Equipment capacity ratings – Understanding that a “12K” unit may actually perform at 18,000 BTU
Latent vs. sensible capacity – Why checking engineering specifications is critical for humid climate applications
VRT (Variable Refrigerant Temperature) – When this energy-saving feature should be disabled in humid climates
Fan operation strategies – Why continuous fan operation can worsen humidity problems
Duct and envelope leakage – How pressure imbalances drive moisture problems
Surface condensation – Why vents and ducts sweat and how to prevent it
The overcooling trap – Why lowering the set point creates interstitial space moisture problems
Humidity sensors in thermostats – Understanding what they do (and don’t do)
Load diversity and zone control – How multiple smaller units can outperform single large systems
Reheat strategies – From electric resistance to passive solar gain
Common mistakes – Why attic insulation and solar fans often worsen humidity issues
Troubleshooting checklist – A systematic approach from bulk water to equipment selection

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VRF, Ductless and Humidity Control w/ Roman

11/27/2025

Bryan Orr

The History of the Thermostat – Short #267

11/25/2025

Bryan Orr