Suppose a house has 15 cm of blown-in cellulose insulation above the ceiling and inside all exterior walls. The thermal conductivity of the insulation is 0.040 W/(K-m). The interior of the house is a box 15 m long by 10 m wide by 3.1 m high. When the outside air temperature is 1.6°C, and the interior temperature of the air in the house and the ground under the house is 21.1°C, how much heat is lost through the walls per hour?

How much heat is lost through the ceiling per hour? 

The house has a furnace that runs on natural gas. Natural gas provides heating of 1.083 megajoules per standard cubic foot (MJ/scf). (MJ is megajoules. Standard cubic feet (scf) is a non-metric unit for measuring the quantity of natural gas.) How much natural gas needs to be burned per hour to keep the air temperature steady in the house? 

 If an additional 12 cm of insulation is added above the ceiling, how much less natural gas is used per hour?