For all those Replacement Window questions
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Curious why the NFRC ratings differ (albeit minimally) between the Okna 500DX and the 800DX when the glass packs are the same? Is that due to the frames? In the end the numbers are very good for either unit.
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The 800 series has the reinforcement in the rails of the sash as compared to foam in the 500 (if both deluxe) and the metal hardware is slightly thermally bridging as compared to none.
Makes sense. Thank you.
Keep in mind Beano that the u factor for the entire unit as tested and certified by the nfrc is profoundly affected by the window assembly, not just the glass. You could take that same glass from the Okna, put it in another window, and get a far worse rating. It is a simple surface 2 low e coating from Guardian. Many other windows offer the same glass, and many others still use a similar coating profile from a different manufacturer like Cardinal. For instance, in a wood window, you may actually get worse than a .30 which was the previous Energy Star threshold... It is everything else that goes into both the assembled IGU, as well as the window assembly overall that has such a major impact on U factor.