Electrical resistance heat may be used as either a primary heating method such as, electric baseboard, electric radiant, electric furnace and electric boiler, or it is used more commonly as a back up heating source in a heat pump installation. Heat pumps are used to provide both air conditioning and heat to a home. In the heating mode they are effective in climates where temperatures seldom go below 45 degrees Fahrenheit. When the heat pump can no longer acquire enough heat from the ambient exterior air the auxiliary electric resistance heating elements turn on automatically to supplement the unit and supply adequate heat. The system then functions as an electric furnace. Electric resistance heating is common in areas where systems are not used for extended winter months or where electricity is economical. The inspector will pay careful attention to not only the function of the system, but the requirements of a large electrical supply to the home as it relates to the electrical system itself. This is the most common problem of systems installed in expanded homes and older homes. The electric service must be adequate for the installation of electric resistance heat.