I have some Anderson windows installed in 96 I think. They are double hung and I believe they're double pane. They were installed before I moved in. What are the odds that these are low-e windows? I ask because we're willing to replace a few of them, especially those on the north side of the house where it's cold. In the brutal winter here in the midwest, it's pretty chilly next to these in the evening. And if they are low-e and should be well-performing windows, would it make since to take off the trim and replace the fiberglass insulation in the shim space with low-expanding spray foam for windows and doors? Thank you!

i have been a buyer for windows and doors since 2000 and i know LoE has been around since the early 80's although not used widely until the 90's. You might contact Andersen who might ask you for a code that might possibly be on the window somewhere or on the glass that can tell them what time of glass is in your windows. As far as taking the trim off and finding insulation in the shim area. Very unlikely unfortunately alot of builders don't insulate that area (could be wrong). But if you do insulati with foam make sure it is the low expanding otherwise you will bow out the frames. I would put new insulation in but make sure you don't cram it in there, just place it in there. A strip of insulation that is still fluffy has a better R-value than the same stirp smooshed down to nothing.

Low E coatings on windows are older than you might think. The very first low-E coatings were highly reflective silver coatings on evacuated glass bottles (aka "dewar" or "thermos" bottles), back in the 1890s. Half-silvered/aluminized window glass for security has been around at least since the 1930s, but the more selective coatings on window glass designed for air-conditioning load reduction on large glass buildings was commercialized by the Belgian company Glaverbel back in the early 1960s. There was at least one German company producing a gold-sputtered low-E glass back then too, but the expense wasn't amenable to large scale use in building apps.

Sealed multi-pane windows (low-E and otherwise) didn't get a lot of traction in the US until the late 1970s.

But this is totally irrelevant for figuring out your 1990s-vintage Andersens, eh? ;-)

Most low-E coatings have a sheen or slight tint in the visible region that you'd be able to notice if comparing side-by-side with clear uncoated glass. The commonly used indium tin oxide hard coat appears as fairly clear but slightly brownish gray filter compared to clear glass. Sputtered silver (usually only on heat-rejection windows for cooling dominated climates) is a somewhat purer-gray, and sometimes noticeably reflective from the exterior. If your Andersens are double-pane low-E these are the most likely coatings. But if it's noticably chilly standing next to it even when it's above 40F outside, it's probably not a low-E window.

But adding a low-E storm window over a clear-glass double pane can make a difference that you can feel, for far less cash than a replacement window. The combined U-factor for a low-E storm over a U-0.5-0.6 double-pane runs in the low U0.3 s or better. (google "low-E storm window" for more info- they're out there, and they're not outrageous. Harvey has a VERY tight storm window with a low-E option, and the better-grade Larsen "Gold Series" aren't bad either.)

For insulating around windows it's safer to air-seal & insulate only the outer 1/3 of the depth with foam, and do the rest with blown/stuffed fiber.

Begging to differ somewhat with BRINDASBABY, smooshing in shredded batt IS the right way to go, so long as it evenly fills the space. A higher density will result in a higher R/inch, (and thus higher net R.) An R19 batt runs ~R3.4/inch, (R19/5.5" )but has the exact amount of fiber as an R13 batt running R3.7/inch (R13/3.5"). It's the same amount of material, it's just less "smooshed". R15 batts are even quite a bit higher density still! If you pack it in with a hammer you will reach a density at which R values fall off, but you'd have to have the fingers of Goliath to hit that with your hands. Fiberglass will top out at about R4/inch if pushed to a fairly springy density, but go ahead and stuff it in there pretty good to be sure that it doesn't leave any voids where it hits your bubbled-up low expansion foam. If you compare it compression-wise to an R13 batt that's been pushed to ~2-2.5" rather than 3.5", that would be fairly optimal. As long as you fill the available depth, you're good.

this is directly from Owens Corning regarding installing insulation in cavities. So if you don't have enough space for using the full thickness then yes compress but if you do it is best to leave as it comes.

• Insulation should not be
compressed when the full
thickness space is available, as
this results in a reduction of
R-value.

Owen's Corning (and others) also publish the R values for compressed batts at standard stud-depths too, and they consistently deliver a higher R/inch when compressed.

http://numsum.com/spreadsheet/show/21111

http://www.owenscorning.com/around/insulation/CompressionChart.xls

^^^^ note that the R13 when compressed in to a 2.5" cavity hits R4/inch @ 2.5", up from R3.7/inch @ 3.5", which is about the density you're going for.

Also note that R22s only perform at R19 in the 2x6 cavities they were designed for, and R19s only perform at R18 in a 2x6 cavity. Both are measured & labeled at their full-loft, not the installed thickness in a wall cavity, which is something of a marketing slight-of-hand somehow allowable at the edges of FTC regs.

It's the reduced thickness that results in the lower-R for batts, not the higher density. With higher density the R/inch goes up, but for a given batt it's much fewer inches. As you fill the full available space you achieve a higher R value by stuffing it a bit harder, up to about 1.5-2x the density of an R13 batt, which is pretty easy to gauge with a finger-compression test. As long as it's still not so stuffed that it still springs back a bit you're at about R4/inch, which is as good as it gets with fiberglass & rock wool.

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