What’s the difference between REM/Rate and REM/Design?

Simply put, REM/Design is REM/Rate, but without the functions that RESNET restricts for the use of HERS Raters.

In practice, that means any reports or features that show a HERS Index or any of the other ERI variations are not available in REM/Design.  All of the core functions are the same in both, including basic results such as predicted loads and consumption, the availability of IECC compliance reports (excluding the ERI, of course), and additional features like the Improvement Analysis (used for existing homes).