Field Notes
HVAC how-tos & product updates
Practical walkthroughs from the field — the numbers that matter, and what they're telling you. Each one links straight to the tool that does the math.
- Refrigerant3
- Airflow1
More field notes
- Refrigerant6 min read
Subcooling, explained: charging a TXV system by the numbers
On a TXV system the valve holds superheat steady, so subcool is your charging number. Here is how subcool works, how to read it, and how to charge to a target without chasing your tail. - Refrigerant5 min read
Target superheat for fixed-orifice systems
A piston does not adjust, so on a fixed-orifice system you charge to a target superheat that moves with the weather. Here is how to find that target from indoor wet-bulb and outdoor dry-bulb — and charge to it. - Airflow6 min read
Duct sizing without the guesswork
Equal-friction duct sizing comes down to two numbers — the CFM a run carries and the friction rate you design to. Here is how it works, the velocities to stay inside, and how to size a round duct in seconds.