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re: winterizing windows: insulator
23 oct 1998
janine wrote:
>...a neat way to winterize your windows...
nice... a friend of mine covers almost all of the windows in his house
this way in the winter, and has very low heating bills. he just cuts the
foamboard to fit tightly and pushes it into the window frames. it seems
to me that most houses have too many windows.
a "well-lit office" has about 50 footcandles of illumination (50 candles
1' away, a lot more than bob cratchit or abe lincoln used. i can read
in 0.1 fc, eg 1 candle 3' away.) full sun is about 10,000 fc, 200 times
brighter than a well-lit office. so... if we spread the light around
uniformly with a reflective light shelf below and a white ceiling and
walls, a square foot of window or skylight might provide all the light
for a 10x20' room at noon... but many houses have 10% vs 0.5% of the
floorspace as windows, 20 times more than they need for 1998 light. the
boca code requires that at least 8% (or 4%, depending on interpretation)
of the floorspace of a house be windows. windows are expensive luxuries.
where i live, in colonial times, when a dollar was serious money, windows
ostentatiously facing the street were taxed at $1 per window per year.
>material:
>1 or more 1/2" styrofoam sheet (4'x8)
i've used 2" foamboard for this. less fragile, more insulative
(adding r10 to an r2 double glazed window, vs r20 for a wall.)
>carefully measure your window, length and width. using a ruler, outline
>the measurements of your window on the stryrofoam sheet...
it needs to fit tightly to avoid condensation on the inside of the glass.
>pop in place and enjoy the savings.
in my 5,500 (f) degree-day climate, each square foot of r2 window leaks
5,500x24h/r2 = 66,000 btu per winter of heat, equivalent to 1/2 gallon
of oil. adding 2" of foamboard reduces this to 5,500x24h/r12 = 11k btu,
saving 55k. insulating 90% of the 200 ft^2 of windows in a 2,000 ft^2
house this way in the winter would save 180ft^2x55k = 9900k btu, 76 gal
of oil per year (or a cord of wood, or 9,900,000 kitchen matches :-)
>be sure to remove these if your window gets sun exposure...
or make them solar air heaters... loosely glue some dark window screen
to the outside of the foamboard, use a couple of spacers so there's a
1" gap between the foamboard and the glass with the board installed,
and cut the board so there's a 2" gap at the top to let warm air rise
up and out into the room during the day. a south-facing version collects
the heat equivalent of about a gallon of oil per year per square foot,
where i live. (the unfoamed window is an even better solar collector,
with a lower temperature next to the glass and less thermal loss to
the outdoors, but it loses lots of heat at night and on cloudy days.)
one might do this to non-south-facing house windows as well, for
additional light and peephole views and convenient handles and
condensation control. where i live, unshaded south-facing windows
transmit an average of 750 btu/ft^2 per day of sun in january.
west, north and east windows transmit 300, 130 and 290.
>sealing your window with caulk and weatherstripping will make your
>insulator more effective>
this would increase the chance of condensation. one might even want
to "unseal" it a bit, eg drill a small hole to the drier outdoor
winter air, if the foamboard covers the entire window.
nick
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