Originally Posted By: Brian Maloney
This post was automatically imported from our archived forum.
Most windows are coming double pane nowadays. Windows are rated in U-Value, which in the inverse (1 divided by the U-value), is its R-value (Resistance to heat loss). A single pane is rated 0.88 R-value. A double pane window with good seals can be as bad as 1.76 R-value; with Argon gas and Low-E coatings they can move up to 2.8 to 3.2. Since different companies fill different % of argon or use better (soft-coat rather than pyrolitic) and more (2 rather than 1) Low-E coatings, the r-value can get as high as 4.2.
Many replacement windows are poorly manufactured. So seals between moving parts can be poor allowing drafts, or meeting rails sag because of the weight of the 2 or 3 panes of glass on the relatively weak and flexible vinyl. A few mfgs internally brace the vinyl with wood, metal or fiberglass to reduce sagging and flexing. Some windows are rated for 165-180 mile hurricane conditions.
Air infiltration ratings are another measure of window quality.
Then some window manufacturers add third pane, better edge intercept sytstems, and 98% fill of krypton gass (the heaviest now available) and get the glass area up to an R-10 (remarkable!).
Window manufacturers get ratings of their frames from R-2.5 to R-20. Some are better insulated than others.
Some owners should add value to their houses by promoting the transferrable warranty that certain replacement windows offer. Many windows have Lifetime (pro-rated or non-pro-rated) for original owners, or if transferrable to next owner, expiring at 50 years.
Brian Maloney, NACHI
Valley Forge Chapter