The HVAC system in your house operates on three basic components that are a source or cool or warm air, a system for distributing the cooled or warmed air to all the rooms and finally a method of control to regulate the system such as thermostat. In this case the source of warm air will be the furnace and the air conditioner for the cool air; these two use the same distribution and control systems in most homes. For homes that have central air conditioning. Both cool and warm air will flow through the same ducts and the same thermostat will be used to regulate them between lower and higher. Any problem with the heating or cooling system that occurs will be associated with the malfunctioning of any of those three components.
All heating and air conditioning units burn some sort of fuel; air conditioning systems consume electricity while the furnace uses fuel oil or gas even though there are newer systems that use electricity as well. There are systems that heat pumps, which is an electrically operated HVAC system that can heat and cool air; it will extract hot air from your house during summer while during winter it pulls heat from outside air which it warms and circulates throughout the entire house. While this may look like a simple operation, there is need for regular heating service if you are going to avoid expensive furnace repairs.
Whenever you turn on the furnace it will definitely consume the fuel which powers it whether it is electricity, gas or fuel oil. Heat is produced when the fuel is burned and is channeled throughout the house through a system of ducts, wires and pipes before it is blow out from radiators, registers or heating panels. There may be older systems that generate heat by heating some water which is in turn used to heat that air in your home. These systems operate on a boiler that heats and stores the water which it circulates using pipes placed on the floor, walls and ceiling.