Electric heat pumps are technologies that in the right circumstances can be cost-effective sources of heating. In a cold climate they frequently complement more typical energy sources such as oil or natural gas boilers in order to reduce total energy costs. To be cost-effective, however, the savings on oil and natural gas from using the heat pumps must be large enough to justify both their initial costs and the subsequent cost of the additional electricity to run them. Would you expect the number of heat pump sales to be affected by the magnitude of local interest rates? Why or why not?