Refprop 91 Free (2026)

The search for "REFPROP 9.1 free" is a common path for students and engineers, but the real story behind it is one of high-stakes science, precise engineering, and the strict rules of professional software. The Mystery of the "Free" Version

In the world of thermodynamics, NIST REFPROP (REference Fluid PROPerties) is the gold standard for calculating the behavior of industrial fluids and refrigerants. Because it is such a critical tool, many users go looking for a free version of REFPROP 9.1, but the reality is that the full software has always been a paid product distributed by the National Institute of Standards and Technology (NIST).

The "free" versions found on the internet often fall into two categories:

The "Mini" Version: NIST offers a legitimate, free sample version called mini-REFPROP. It is designed for students and includes only a few common fluids like water, methane, and nitrogen. refprop 91 free

Legacy and Superseeded Versions: Version 9.1 was a major release in 2013, but it has since been superseded by Version 10. While some third-party sites might list "free trials" for 9.1, these are often just installers for the "mini" version or unofficial files that NIST does not support. Why People Still Search for 9.1

Despite being over a decade old, many engineers still search for 9.1 because:

Disclaimer: This article is for educational and informational purposes only. NIST REFPROP is a copyrighted, proprietary software. This guide does not provide cracked software, license keys, or links to pirated content. It is intended to help you find legitimate, free alternatives and understand the legal risks associated with "free" downloads. The search for "REFPROP 9

If you work in thermodynamics, chemical engineering, or HVAC research, you are likely familiar with REFPROP. It is the industry-standard reference fluid thermodynamic and transport properties database developed by the National Institute of Standards and Technology (NIST).

With the recent release of newer versions like REFPROP 10 and 11, many users are looking for information on the older, but still capable, REFPROP 9.1. Whether you are looking for legacy compatibility or simply trying to understand the differences between versions, here is your guide to REFPROP 9.1.

If you cannot obtain a licensed REFPROP, consider these free/open options (varying in accuracy and available fluids): If you work in thermodynamics, chemical engineering, or

  • IAPWS libraries (steam/water)
  • Thermo (Python package)
  • Engineering Toolbox / online calculators
  • Proprietary commercial alternatives (if budget permits)

    • For students: Using a cracked REFPROP 9.1 violates most university honor codes. Professors can detect inconsistent results from legitimate versus cracked solvers (cracked versions often corrupt equation solvers to bypass license checks).

    No. NIST REFPROP has never been freeware. A single-user license for REFPROP 9.1 was ~$325 (later versions are $375+). However:

    REFPROP, developed by the National Institute of Standards and Technology (NIST), is a comprehensive software package that provides detailed property data for refrigerants, including thermodynamic properties, transport properties, and phase equilibrium data. It's essential for engineers and researchers working with fluid dynamics, HVAC (heating, ventilation, and air conditioning), refrigeration, and chemical engineering.

    REFPROP's equations of state (like ECS, TC, and viscosity models) are complex. If your crack gives a wrong saturation pressure for ammonia at 300K, you have no official forum, no NIST helpdesk, and no patch. Your research or design could be dangerously flawed.

    For programmers: The Cantera library (cantera.org) includes thermodynamic models comparable to REFPROP 9.1 for many gases. Combined with Python’s SciPy, you can create your own REFPROP-like scripts for free.