Please try this guide for running multiple versions.
The key idea is: each version should go into its own folder.
The following procedure uses 14.5 and 14.6.2 as an example, but you can substitute any other version.
How to install:
Let's say you want to have both versions 14.6.2 and 14.5 installed.
Normally, the REM installer does not distinguish between minor versions. By default, both 14.5 and 14.6.2 will install into the same folder,
C:\Users\Public\Architectural Energy Corporation\REM Rate 14
To install 14.5 into its own folder, when you run the installer and reach the "Install Location" screen, click the "Change" button, and in the Path field, change "REM Rate 14" to "REM Rate 14.5". Then continue with the installation.
For 14.6.2, do the same procedure, but change the destination path to "REM Rate 14.6.2".
How to run:
There will be a Start menu shortcut for REM, but it's unclear which version it points to.
So how do you run a particular version?
I recommend making new shortcuts for each version.
In the file explorer, go to
C:\Users\Public\Architectural Energy Corporation\REM Rate 14.5
Select the file REMRate14.exe, and drag it to the desktop to make a shortcut.
Rename the shortcut to "REMRate 14.5".
Do the same procedure for 14.6.2.
How to open .blg files:
Double-clicking .blg building files is another ambiguity. Will it open in 14.5 or 14.6.2? (Note, you would have a similar problem with multiple versions of Excel installed.)
To guarantee a file is opened in the right version, you should run the version of REM wanted, then use File Open menu, or drag-and-drop the .blg file onto the REM window.
Sharing of files (.blg and library files) between versions can be problematic. While newer versions can read older files (backwards compatibility), older versions might not be able read newer files.