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window insulation question: OT

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Posted by Jeff Thies on December 26, 2005, 6:00 pm
   I live in an old house (30's).

   Looking at the single pane window. I've read that the glass part has
an R value of about .9

   Softwoods (the window frame) have an R value of about 1.4/inch and
hardwoods have an R value of about .8/inch.

    I'm having a hard time believing that an inch of wood could have an
insulation value less than 3/16" of glass.

    There must be a boundary issue with the R value. Can someone explain

   Also, what is the approximate R value of my old walls? It's wood
siding, with a plaster inside. I doubt that there's any insulation. My
non scientific guess would be a 3 or 4. Perhaps I need an IR spot
thermometer and measure indoor air, outdoor air and wall surface temp...


Posted by nicksanspam on December 27, 2005, 5:54 am

The glass itself has little R-value. The 0.9 comes from a slow-moving
indoor (~R0.67) plus a faster outdoor (~R0.17) air film.

With heat flow across the grain, and about 1/3 of that parallel to the grain.

Comparing apples to apples, you would also add the air films to
the wood's thermal resistance.

Maybe a little lower. Air leaks count too.


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