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re: hot water heater
1 jan 2001
ben wrote:
>a booklet i received from my propane company last week claims that
>lowering the temp of the hot water heater from 140 to 125 will reduced
>enery costs by 1/2. sorry but there are no data presented nor are
>any references given...
this could be an overestimate. with a perfectly insulated tank,
heating 50 f water to 125 vs 140 f requires 100(125-50)/(140-50)
= 83.3% as much energy. this becomes 78.6%, starting from 70 f.
maintaining a tank with 30 ft^2 of r10 insulation at 125 f in a 70 f
room requires 24h(125-70)30ft^2/r10 = 3960 btu/day vs. 5040 at 140.
taking a 110 f shower requires about the same energy either way (with
more hot and less cold water at 125 f.) a washer and dishwasher with
no internal heaters would use more energy if consuming, say, 30 gallons
per day of 140 f vs 125 f water, eg 30x8(125-50)/0.8 = 22.5k btu at 125 f
and 27k at 140 f, at 80% efficiency, starting with 50 f water.
but (3960+22.5k)/(5040+27k) is only 82.6%...
nick
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