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.
How to measure superheat (and what your number means)
Superheat is just suction line temp minus saturation temp — but reading it right, and knowing whether the number is telling you about charge, airflow, or your metering device, is where techs get tripped up.
Read itSubcooling, 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.
Read itTarget 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.
Read itDuct 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.
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