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Dave has a home in Pittsburgh, PA (HDD = 6,000) with a roof area of 1894
ft2. He is considering upgrading the insulation from R16 to R28. The
estimate for this job from the contractor is $902. Dave's home is heated with
natural gas. Last year, the average price he paid for natural gas was
$14.1/MCF. Assuming an AFUE of 87.5%, how long will it take Dave to
recover his investment (in years)?
Correct
B ) 7.7 Years
Cost of insulation = 902 / 1894 = 0.4762 $/sq.ft
Cost of energy = 14.1 / 1,000,000 = 0.0000141 $/BTU
Time to recover investment = (0.4762 x 16 x 28 x 0.875) / (0.0000141 x (28
 16) x 6000 x 24) = 7.66 yrs
A house in State College, PA (HDD=6000) has 344 ft2 of windows with R
value = 2.5, 1804 ft2 of walls
with R value = 18, and 1101 ft2 of roof with
an Rvalue = 28. What is the total heat loss from the house for the season (in
BTUs)?
Correct Answer:
C ) 39908685.71 BTUs
Heat lost through windows = 344 x 6000 x 24 / 2.5 = 3302400 BTUs
Heat lost through walls = 1804 x 6000 x 24 / 18 = 2405333.33333333 BTUs
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 Fall '06
 MATHEWS,JONATHAN

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