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re: hot water heating
7 may 1997
leslie gratton wrote:
>now, as i understand it, (and i freely admit i could be wrong) to heat
>water up to the usable temperature uses considerable energy. however, to
>maintain said temperature uses comparatively little...
yup. heating up 60 gallons of 50 f water to 120 f takes about 60x8x(120-50)
= 33.6k btu or about 10 kwh. keeping it warm for a day in a 70 f room in
a 1' diameter x 8' tall tank surrounded by 6" (more than most tanks) of
fiberglass insulation takes about 24(120-70)27ft^2/r20 = 1600 btu or 0.5 kwh,
about 5% of the energy needed to heat up the water. turning off the power
for 24 hours lets the water cool 1600/(60x8) = 3 degrees f, so the water
heater only loses about 24(120-3/2-70)27/20 = 1566 btu, saving a grand total
of 34 btu or 0.01 kwh/day worth 0.001 cents at 10 cents/kwh, so one might save
about 1 cent every 6 years if one did this every other day, or maybe 10 cents
every 6 years, if one only washed dishes and bathed on saturday nights :-)
nick
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