Subcool: HVAC PT & Superheat

New for the A2L changeover: R-454B and R-32 in full. Superheat, subcooling, duct sizing and psychrometrics, with no account needed.

Subcool is the calculator an HVAC technician actually reaches for at the unit.

Pick the refrigerant, enter the gauge pressure and the line temperature, and read the answer. No account, no subscription, no upsell in the middle of a service call.

SUPERHEAT AND SUBCOOLING, DONE RIGHT

Superheat is measured against the dew point and subcooling against the bubble point. On a blend like R-407C those are more than twelve degrees apart, so an app that quietly uses the average column is wrong in both directions at once. Subcool knows which curve each measurement belongs to and picks it for you.

Saturation values are interpolated from the refrigerant manufacturer's own published pressure-temperature chart, and every result names the chart it came from.

R-454B AND R-32, FREE

New residential systems in the United States moved to A2L refrigerants in January 2026, and the pressures are not the ones anyone learned on. Subcool ships fifteen refrigerants and every one of them is free: R-454B, R-32, R-410A, R-22, R-134a, R-404A, R-407C, R-448A, R-407F, R-450A, R-507A and the older interim blends still out there on equipment nobody has replaced yet.

Nothing about charging a system sits behind a purchase. There is no counter, no daily limit and no trial that runs out.

FREE FOREVER

• Every refrigerant, including both A2Ls
• Superheat and subcooling, with a plain reading of what the pair suggests
• Target superheat for fixed orifice systems from the indoor wet bulb and outdoor dry bulb
• Delta T, airflow, and CFM per ton
• Ohm's law, single and three phase power, capacitor microfarads from measured volts and amps, voltage imbalance
• Imperial and metric throughout

SUBCOOL PRO

One payment unlocks the engineering side and the paperwork:

• Duct sizing for round and rectangular duct at any friction rate, with real velocity and the equivalent size a sheet metal shop can cut. Friction comes from Darcy-Weisbach with the Colebrook-White factor, not from a scanned wheel.
• Total external static against what the air handler is rated for, so you can tell a duct problem from a fan problem.
• Full psychrometrics: relative humidity, dew point, grains, enthalpy, specific volume and mixed air, from the ASHRAE equations, with altitude correction. Set your site altitude once and the airflow constants stop being sea level numbers.
• Combustion: clock the gas meter to find what a furnace is really firing at, check the rise against the data plate, and work out steady state efficiency.
• Save every visit against a customer and a machine, with photos of the nameplate, and export a PDF service report and a CSV with your company on it.

BUILT TO BE CHECKED

Subcool computes. It does not certify. Every result carries the source it came from and a reminder to check the data on the unit, and the diagnostic notes say what a set of readings suggests rather than pretending to know what is wrong with somebody's system.

PRIVATE BY DEFAULT

There is no account, no analytics, no tracking and no networking code in the app at all. Your customers, your job records and your photos stay on your iPhone.