There are three main parts of a heating system: the furnace (or heat source), the ductwork (air circulation system), and the thermostat. Most California homes have a furnace, so we will be assuming that heat source in this description. The furnace is the part of the heating system that provides hot air. The ducts take the hot air to different rooms in your home. Finally, the whole system is controlled by the thermostat.Depending on the size of your home, you may have a lot of ductwork or multiple thermostats. The basic components of the heating system remain the same, however. If you have a problem with any of these three components, you will need heating repair or replacement.