Interesting discussion. It's easiest if you can get the "whole assembly NFRC value" which is quite often on the Spec sheet, or even a marketing cutsheet. Sometimes, the fine print of the spec sheet will even say "NFRC values calculated using the Window 6 program" (or whatever version of the Window program they happened to use!) Of course, this ties into what Mr. Ellison says: i.e. just calculate the whole assembly NFRC via the Window program. I have seen comments asking for the specific calculations from the Window 6/7 program . Thus calculating the NFRC with frame effects via the Windows program would be the next step if not provided by the mfg. Regarding the spreadsheet calculations - I'm sure you can do the NFRC calculations via spreadsheet but I have not tried this myself. The Window program is pretty easy to use, maybe easier than a spreadsheet, after you've used it once. Hopefully manufacturers catch on and start including assembly NFRC values as standard data Bob ? On Wed, Apr 2, 2014 at 5:15 PM, wrote: