Particular cost-effectiveness depends on the incremental cost of the heat pump and how much heating you use. There are a number of variables that will affect how economical they are and what the savings will be, especially the simple fact of how much heat you use. All things considered, odds are good that if you use a fair amount of heat each winter, you will save money by buying a heat pump because your heating costs will be lower. This is also a good time to have the ducts pressure-tested and to consider buying a programmable thermostat. The average life of a central air conditioner is about 15 years, depending on how regularly it is serviced.
Heat pumps have about the same life expectancy.
Units that have been well-maintained and newer units should last even longer. Before you buy an appliance that has special features, make sure you plan to use those features. A frost-free freezer, for example, will cost more and take more energy to operate.