What is air conditioning? How home ventilation systems work

Keep your home comfortable with a functional HVAC system.

Almost every home has some HVAC equipment designed to control the temperature and air quality. Air conditioners, heat pumps, and furnaces are all components of an HVAC system. Each works to cool or heat the air, depending on the current temperature inside the home. Use this guide to answer the question: What is HVAC, and how does it work?

HVAC Definition

HVAC is an acronym for heating, ventilation, and air conditioning. HVAC systems control the temperature inside the home through a variety of methods, though most involve pumping air over cooling coils or a heat exchanger to increase or decrease the air temperature. The air is then blown into the home through vents and ductwork.

Some HVAC options, like a boiler and radiator system, don’t involve airflow, and some HVAC units don’t affect the temperature in the home. Other HVAC components increase or decrease the ambient humidity and work to improve air quality. An HVAC system can also have an air purifier to filter bacteria, fungi, viruses, and other debris.

What Does an HVAC Do, and How Does It Work?

The purpose of an HVAC system is relatively easy to understand. The system heats, cools, and filters the air. However, it isn’t as easy to grasp precisely what HVAC systems do and how they work. Typically, an HVAC system pulls in air using a fan and carries the air through the system using a series of ductwork. The air is then pulled over heating elements or carried over refrigerant-filled cooling coils to change the air temperature before being blown through the ductwork and out through the vents into the home.

This process allows homeowners to increase or decrease the temperature inside the home by changing the thermostat setting. Additionally, HVAC systems filter dust, bacteria, and other particles to improve the air quality inside the home by forcing the air through an air purifier or air filter to remove debris. The HVAC system can also control the humidity inside the house as long as the system has a built-in humidifier or dehumidifier.

HVAC systems have three major parts, including a heating unit, a cooling unit, and ducts to carry the air. The most common configuration is a furnace and air conditioner, but some homes may also use a heat pump, boiler, or air handler to control the temperature inside the home. Boilers work differently from other HVAC components because they don’t heat the home with air. Instead, boilers heat water inside a closed system, and the water or steam circulates through the radiators. The heat radiates from the radiators to warm the house.

HVAC Components

HVAC systems comprise a series of components to facilitate a home’s heating, cooling, and ventilation. They can include air conditioning systems, boilers, heat pumps, furnaces, ventilation systems, air handlers, and ductwork.

    • Air conditioning systems are one of the most common additions to a home HVAC system. These systems have a fan that draws in air, pulling it over refrigerant-filled coils to rapidly cool it. The cool air is then sent through the air handlers and into the ducts, where it is released to cool the rooms in the home.
    • Boilers are not as popular as furnaces in a home. This type of HVAC equipment rapidly heats water before releasing it to a network of radiators. The heat from the water radiates from the radiators to heat the home. Some boilers may heat the water until it is steam for use in a steam radiator system.
    • Heat pumps pull warm air from the house and pass the air over refrigerant coils to cool the air. Warm air is then expelled from the building while the cool air is pumped back in to reduce the temperature inside the home. Heat pumps work in reverse when it’s cold outside, pulling in heat from the air or ground outside the home. The refrigerant coils absorb the heat, increasing the air temperature as it is blown over the coils and into the home.
  • Furnaces are a popular choice for homes in cold climates. The furnace uses a combustion chamber to heat a heat exchanger. When air is pulled into the furnace, it flows through the heat exchanger, increasing the temperature of the air before blowing it through the ducts and back into the home.
  • Air handlers are less effective for cold climates than furnaces but can be a good option in areas with mild weather. Instead of a combustion chamber and heat exchanger, air handlers rely on an electric heating coil to warm the air before the blower circulates the air back into the home.
  • Ductwork is a key component of any HVAC system. This part of the system is responsible for carrying the air between the primary components of the HVAC system and releasing conditioned air into the home.
  • Ventilation systems include humidifiers, dehumidifiers, and air purifiers intended to filter out dust, dirt, bacteria, viruses, and other small debris to improve the air quality within the home.

Types of HVAC Systems

Forced-Air System

The most common type of HVAC system is a forced-air system. It is also called a split system because it has one unit inside the home and one outside. Generally, a forced-air system comprises a furnace for heating and an air conditioner for cooling, although this setup can also consist of an air handler and heat pump or a furnace and heat pump.

Some HVAC professionals may refer to a furnace and heat pump setup as a hybrid heat pump system. During milder periods of the year, the heat pump heats the home, but as temperatures drop, the furnace takes over to ensure the home is kept warm through the colder months.

A furnace/heat pump hybrid system saves money on heating costs for most of the year because it is cheaper to heat a home with a heat pump than a furnace.

Mini-Split System

Smaller homes, garages, and workshops may benefit from a mini-split system. Like larger forced-air or split systems, mini-split systems have an outdoor and indoor unit. Ductless mini-split systems pull in warm air from outside and cool it by blowing it over refrigerant-filled cooling coils before releasing it directly into the garage, workshop, or room.

Ducted mini-split systems rely on tubes instead of large ducts to move the air throughout the home. This type of system is best when the home is relatively small or there isn’t a lot of space for traditional ductwork. While ductless systems work well for single rooms, ducted mini-split systems are better for tiny houses with multiple rooms.

Packaged System

While a split system has an outdoor and indoor unit, a package system houses all units outside. This type of setup is ideal for homes that don’t have a lot of available interior space, although they are also a good idea if the goal is to reduce the ambient noise of the HVAC system. Since the units are outdoors, packaged systems are much quieter. Additionally, packaged systems can have lower installation costs, but this depends on the installation company and the existing HVAC setup.

Radiant Heating System

Radiant heating systems don’t rely on airflow to heat the home. Instead, radiant heating systems use hot water or steam from a boiler to produce heat. The hot water or steam circulates through a series of pipes and radiators, which then heat the air in each room to increase the temperature throughout the home. Some radiant heating systems use electric heat cables instead of hot water or steam.