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Consider a house in Blacksburg, Virginia. The typical annual space-heating load for this size of a house is 100 times 10^8 Btu. That is with no insulation in the attic, we lose about 100 times 10^8 Btu per year. With insulation in the attic the amount of heat lost each year will be reduced. The value of energy savings that results from adding insulation and reducing heat loss is dependent on what type of residential heating furnace is installed. Assume that an electrical resistance furnace is installed by the builder and its efficiency is near 100%. The cost of electricity is $0.15 per kWh. The cost of several insulation alternatives and associated space-heating loads for this house are given in the following table. Which amount of attic insulation is most economical? The life of the insulation is estimated to be 26 years