About PT Charts

Who builds it

PT Charts is made by Rocky Mountain Apps. Paul Gunder writes the software behind it: the charts, the calculator and the practice tests. He's a tool builder, not an HVAC technician, so the site doesn't lean on field know-how. Every value comes from a computed model or a saved source, and the methodology page shows which.

Why it exists

Pressure–temperature charts for newer blends like R-454B are scattered across manufacturer PDFs, and some sit behind account logins. Free EPA 608 practice questions are easy to find, but they rarely say which part of the regulation an answer rests on. This site puts the charts in one place, readable without an account, and ties every practice answer to the paragraph it comes from.

How it's paid for

A paid printable chart pack may be offered at some point. The charts, the calculator and the practice tests on this site stay free.

Your inputs

Everything you type into a chart, the calculator or a practice test is worked out in your browser, and none of it is sent to us. The charts and the calculator write your inputs into the page address, so a result can be shared or bookmarked; the practice tests don't. To save you retyping, the charts also keep a few things in this browser's local storage: the refrigerant you used last, the ones you pin, your last eight readings, and whether you asked for °C and kPa, and your field-mode choice. Clear under the recent readings removes the readings, and clearing this site's data in your browser removes the rest. A practice test keeps your picks in this tab's session storage until you close the tab, so a reload doesn't lose them. Pages you open are also kept in this browser's cache so they work without a signal; clearing this site's data removes them.

Found a mistake?

If a value looks wrong or a rule has changed, please say so through the contact page. Corrections are listed on What changed.