If you are worried about downloading an old .exe, here are free, modern alternatives that perform the same job:
McQuay International, now part of Daikin Applied, has long been a titan in the HVAC industry. During the golden age of desktop engineering tools (the late 1990s and early 2000s), McQuay released a suite of selection software that became an industry standard. mcquay duct sizer software free download
If you manage to find an old executable file (usually a .exe file) of the McQuay Duct Sizer, you will likely face compatibility hurdles. If you are worried about downloading an old