Pocket HVACWho I am
I'm Paul Williams, an HVAC technician and the person behind Pocket HVAC.
Working in the field, I know how important it is to have accurate information when you're standing in front of a unit trying to diagnose a problem or verify your readings. Whether you're checking superheat, figuring out subcooling, looking up refrigerant pressures, or sizing ductwork, the last thing you want is to waste time digging through PDFs or second-guessing a calculator.
That's why I built Pocket HVAC. I wanted a collection of tools that I could actually use on the job, with reliable numbers, straightforward inputs, and no unnecessary complications.
I also believe you should be able to see where those numbers come from. That's why every calculator shows the formulas behind it and references the technical sources used to verify its results. That way you can be confident in the numbers you get.
Why I built Pocket HVAC
With refrigerants like R-454B and R-32 becoming more common, having quick access to accurate pressure-temperature information matters more than ever.
The problem is that a lot of the information we rely on is scattered across manufacturer PDFs, reference charts, and different sources. I'll admit that some online calculators are convenient, but they don't explain how their results are calculated or where their data comes from.
I wanted to bring the tools we HVAC technicians use regularly into one place, designed to work just as well on a phone at the jobsite as on a computer.
My goal is simple: give other technicians quick, accurate answers they can verify and trust.
How I verify the numbers
I take accuracy seriously. A calculator isn't much use if it gives you the wrong reading, especially when you're using it to make decisions about a system you're working on.
Here's how the tools are built and checked.
Refrigerant pressure-temperature charts
Most of the PT calculators use CoolProp, an open-source thermodynamic property library that implements published refrigerant equations, including those from NIST. Rather than manually entering values from a chart, the calculators generate their results from these verified equations.
R-448A and R-449A are the exception. CoolProp's models for those two blends put their dew points about half a degree off the makers' tables, so their charts are built from the makers' own published tables instead: Arkema's PT chart for R-448A and Chemours' Opteon XP40 tables for R-449A. Each one is then checked against another maker's chart.
I compare those results against published refrigerant data from sources like Arkema, Chemours, and NIST, including complete PT chart ranges from -40°F to 150°F.
There is one known difference worth mentioning: R-454B bubble-point temperatures can calculate up to 0.6°F lower than the values published by Chemours. To account for this, I've made sure to explain that discrepancy on the R-454B PT chart page.
Superheat and subcooling
For blended refrigerants, using the correct saturation temperature matters. The calculators automatically use the dew point for superheat and the bubble point for subcooling, so you don't have to worry about selecting the wrong side of the refrigerant glide.
Target superheat and temperature split
The reference tables for target superheat and temperature split are based on California's Title 24 energy code.
Duct sizing
The duct sizing calculators follow the ASHRAE Fundamentals Handbook (2025, Chapter 21). I also compare the ductulator's results against ASHRAE's published examples and Duct Fitting Database.
Psychrometric calculations
The air-property calculators use PsychroLib, which implements equations from the ASHRAE Fundamentals Handbook (2017, Chapter 1). Results are checked against ASHRAE reference tables and independently compared with CoolProp.
Beyond those references, I have built automated tests into the site that check calculator results against published values. I make sure to run those tests before updates are released to help catch errors before they reach the tools you're using.
Always follow the equipment manufacturer
As useful as these calculators and reference charts are, the manufacturer's specifications always take priority.
Every system is different, and a general charging calculator can't account for every equipment design, installation condition, or manufacturer requirement.
Use these tools to check readings, run calculations, and help troubleshoot, but always refer to the equipment's charging chart, service documentation, and installation instructions when making final adjustments.
That's how I approach the tools on this site: they're meant to make our jobs easier, not replace proper service procedures.
Found something that doesn't look right?
If a calculator gives you a result that doesn't seem correct, I'd like to know about it.
Send me an email anytime at hello@pockethvac.com with the tool you were using, the values you entered, and the result you expected.
I'll review the calculation, compare it against the published reference data, and correct it if something is wrong.
My goal with Pocket HVAC is to build a resource that's genuinely useful to other technicians, and feedback from other people using these tools in the field is an important part of that!