How Does Central Heating and Cooling Work?

Most of us take heating and cooling for granted. We expect our air-conditioning to keep us cool during the summer and we depend on heating systems to keep us warm during the winter.

All climate-control devices or systems have three basic components: a source of warmed or cooled air, a means of distributing the air to the rooms being heated or cooled and a control used to regulate the system (such as a thermostat). The sources of warm air, such as a furnace and cool air, such as an air conditioner, in a house often use the same distribution and control systems. Both heating and air conditioning work on the principle that heat always moves from a warm object to a cooler one, just as water flows from a higher to a lower level. Furnaces and heaters put heat into the air to make your home warmer; air conditioners remove heat to make your home cooler.

Understanding the central heating and cooling processes will help you better maintain your HVAC system. Once you know the basics, you will know exactly what is going on in your home the next time you hear your HVAC system kick on.

How Does Central Cooling Work?

Central air conditioning is a common term used to describe most whole-home air conditioning systems. It replaces warm air with cool air that has been passed over cold coils, and then pushes it into your living spaces. It is essentially like a giant refrigerator for your house and actually utilizes the same types of components, materials and systems as a refrigerator, including a refrigerant that changes from liquid to gas and back to liquid as it travels through a system of tubes and coils or fins that collect and give off heat.

The typical central AC system is made up of two parts: the outdoor compressor-bearing unit and the indoor evaporator coil. The air is usually transferred by a furnace or air handler. Your thermostat works in conjunction with the system, monitoring the indoor temperature and signaling when warm air needs to be removed and cool air needs to be circulated.

As it goes through this cycle, it gathers heat from one place and transfers it to another. At the same time, it creates cold in one place and delivers that chill to another. A central air conditioner runs on electricity. During summer months, it can consume a lot of energy when it runs a lot, so the efficiency of the air conditioner can be a very important feature. If you are buying a new air conditioner, this means choosing one that is designed for energy efficiency and sized properly for your house.

Remember three main points: temperature control, cooling and air circulation. These three parts make up the bulk of the work that your AC performs to keep your home comfortable. Essentially, the system takes the heat out of the home, transfers it to the coils and, by doing so, cools off the air.

Here are the main steps in the process:

The Central Cooling Processes

Central cooling kicks off when a thermostat senses that the temperature in your home needs to be changed. In the case of central cooling, the thermostat will alert your cooling unit that the temperature needs to drop and all parts will work simultaneously to get your home to your desired temperature. Once the systems are alerted, they take these steps to cool your home:

  • When the indoor temperature rises above your desired set point, the thermostat turns on the system.
  • The fan in the indoor unit pulls warm air from inside your home into return air ducts, and then passes it through filters to remove dust and airborne pollutants.
  • That air passes over the cold evaporator coil, where liquid refrigerant absorbs heat, changes it into a gas refrigerant and cools the air.
  • The blower fan then sends the cooled air into living spaces.
  • The now-warm gas refrigerant travels to the compressor through copper tubing.
  • The compressor pressurizes the gas and sends it to the condenser coil, which releases the heat outdoors and turns the refrigerant back to liquid.
  • The refrigerant travels to the evaporator coil to continue the cycle.

How Does Central Heating Work?

Central heating systems can work in the same general way as central cooling systems by moving air around to change the temperature in your home. Air conditioning may be the top priority for Southern Californians when it comes to temperature control options, but central heating is just as important during cold winter nights.

Central heating comes in several forms, most typically a gas driven heater or a reverse cycle air conditioning system. The primary heating appliance, such as a furnace or boiler, is typically located in an out-of-the-way place such as a basement or garage. It delivers heat throughout the house either by pumping warmed air through a system of air ducts or sending hot water or steam through pipes to room radiators or convectors.

With both forced-air and gravity systems, one or more thermostats turn the heating or cooling unit off and on as room temperatures rise and fall. Homes without central heating normally utilize electric baseboard heaters or, in some cases, in-wall or in-floor gas heaters or radiant heat.

A heat pump can provide both heating and cooling. In the winter, a heat pump extracts heat from outside air and delivers it indoors. On hot summer days, it works in reverse, extracting heat from room air and pumping it outdoors.

The Central Heating Processes

The process works by using natural gas or liquefied petroleum to power a central gas heater, which are usually installed outside a house but can also be installed under flooring or other permanent fixtures with relative ease. The unit draws in cold air from inside your home with a fan and then pushes the cold air over a heat exchange, which uses a process known as gas combustion to warm up the air.

When the temperature drops and a heat pump needs to provide heat, the process essentially reverses itself. Once a heat pump registers the function shift, a reversing valve in the outdoor unit kicks on. This allows the heat pump to absorb heat energy from the outside air and transfer it into the home to warm it up, instead of taking heat from the home and putting it outside to cool it down. The reversing valve is never something that the homeowner needs to touch; the heat pump knows to switch functions on its own!

Furnaces, on the other hand, function in a totally different way than other HVAC products. While the thermostat still kicks off the heating process, all furnaces produce heat from a gas source, like propane. Depending on the type of unit you own, the gas source could be located in an outdoor unit or underground, but both will be connected to your home via a pipe. Once your gas source is connected, the furnace follows these steps to raise the temperature:

  1. Gas comes into the furnace through the pipe and lights the furnace burner.
  2. Cold air from your home meets the burning gas. The cold air is warmed via the gas within the furnace heat exchanger.
  3. Exhaust from this interaction between the cold air and hot gas is piped out of the furnace through a vent and then put outside your home via an exhaust pipe.
  4. A blower fan inside the furnace directs the newly warmed air through the various ducts in your home.
  5. More cold air is directed from your home into the furnace via the return ducts.
  6. The process repeats itself until your home is warmed, at which point the gas valve switches off and the furnace stops producing heat.

How the Heat Is Generated?

The first step, of course, is to generate the heat that will be circulated throughout the home. There are many methods of doing so, each with its own advantages and drawbacks.


  • Gas Heat

Gas heating is extremely common in millions of homes all over the country. For this, propane and natural gas are the most common fuel sources. The benefit of a gas-powered furnace is that it heats up very quickly and burns very hot. Even the coldest parts of the country are no match for the toasty temperatures generated by a gas furnace.

The major drawback for a gas furnace is access; if your home doesn’t already have a gas main hooked up to it, it can be prohibitively expensive to have one added. Still, it may be your best option if you live somewhere where the temperature regularly becomes very cold.


  • Electric Heat

Another popular option for generating heat is electricity. This has the benefit of being much more easily accessible than other methods. Because it doesn’t require burning anything to use, it also is safer than other methods.
Electricity, however, does take longer to achieve your desired temperature and electric heating coils can struggle against temperature extremes. A power failure can also leave you without any heat for your home.

Final Thoughts

Understanding heating and cooling product installation is important before you buy an HVAC system. HVAC systems should always be installed by a licensed HVAC professional and homeowners should never attempt any kind of installation or maintenance on their system themselves. But there are steps you can take before installation to ensure everything runs smoothly and your HVAC device is the perfect fit for your home.

If your air conditioner is not running properly and you are not experiencing better air conditioning efficiency after completing the above tips, it might be time to call a professional service technician at Aire-Tech. Our highly trained and skilled technicians will check your unit or units for proper air flow and coolant levels as well as clean internal coils and perform other repairs if required.

If your system needs repair or inspection before spring or summer, call us on 951-926-1002. You can also visit our Contact page and complete the contact form.