To install a furnace, first determine the type of furnace you want to install. There are two major types of furnaces: gas furnaces and electric furnaces. Gather all tools and materials before getting started. Assess the home to know how old the windows are, the type of insulation present and if there is an air infiltration system. Check to be sure that the existing ducts are going to fit the new furnace.
To install a gas furnace, shut off the gas and power supply to the furnace. Remove the old furnace to make space for the new one. Align the new furnace with the existing gas pipes and duct work. Install any doors, switches and wires to the internal furnace.
Connect the existing duct work to the new furnace, and attach a boot to it. Connect the gas line to the furnace, and inspect it for leaks. Connect the thermostat and power supply. Wait for at least five to 10 minutes before lighting the furnace.
To install an electric furnace, switch off the power from the main switch, and disconnect all the wire cables from the old heating unit. Examine existing wires for fraying, wear or tear, and do the necessary repairs. Put in the new electric furnace, and allow it to sit and fit in the position of the old furnace.
Make the necessary changes if not enough leads are coming from the heater to the ducts. Plug the furnace into a working electrical outlet. Test the electric furnace to ensure it is connected and working properly.