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Tech Tips:

HVAC systems often fail early or don't perform well due to inconsistent power. While technicians can't control a home's main power supply, they can stabilize it at the system using buck-boost transformers. These devices adjust voltage up or down to meet the equipment’s needs. As HVAC systems become more advanced, understanding buck-boost transformers will be […]

The Current War – Tesla, Edison & Westinghouse – Short #266

In this short podcast episode, Bryan is back for yet another history lesson. This time, the subject is the current war with Tesla, Edison, and Westinghouse. The current war was fought in the late 1800s with lightbulbs, electrocutions, and a World's Fair that dazzled the entire world. Edison didn't necessarily invent the lightbulb, but […]

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In this short podcast episode, Bryan explores the history of the finned-tube coil, which is what we use for heat exchange in air-source air conditioners and heat pumps.

Air-source HVAC systems have copper tubes threaded through thin metal fins. This design was optimized to ensure the greatest possible surface area for heat exchange to occur. However, prior to the finned-tube coil, HVAC coils looked more like plumbing projects with bare copper loops, which were heavy, costly, and inefficient.

In the early 1900s, HVAC was essentially plumbing with higher expectations; capacity was dictated purely by size and charge. In the 1910s and 1920s, early air conditioning pioneers were already attempting to increase surface area with metal discs or pipes, which evolved to continuous sheet fins. The tube would move refrigerant, and the fins would collect heat from the air and pass it into the tube; the finned-tube coil was born. The added weight was minimal, but the contact area was increased by almost 3000%, meaning coils and charges could be smaller with added efficiency.

This move was necessary because while we already knew that heat can indeed move without touching molecules (radiant transfer), radiant cooling had a unique challenge: dew point. Finned-tube coils rely on convection and only have temperatures below the dew point in a small area, which allows us to have a small drain pan. Aluminum was also plentiful after WWII, enabling finned-tube technology to evolve to louvered fins and reach the masses. By the 1960s, finned-tube coils were in all sorts of applications. However, it became clear that aluminum was fragile, and we have since innovated to overcome that challenge.

There are three barriers that heat transfer must overcome: air-side film resistance (air is a poor conductor), wall conduction through the tube and fins, and refrigerant-side film resistance (oil inside or laminar flow). The fins help with air-side film resistance, so we want to clean and straighten them as much as possible.

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The Finned-Tube Coil – Short #269

12/09/2025

Bryan Orr

Are Two Are Better Than One: Understanding Tandem Compressors

12/04/2025

Bryan Orr