What Is HVAC and How Does it Work? (2024 Guide)

By Amanda Lutz Updated January 9, 2024

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Homeowners in areas with mild weather year-round can often use natural ventilation to keep their homes comfortable. However, most of us need help from residential heating, ventilation, and air conditioning (HVAC) systems. These vital home systems heat or cool the air, filter out particles, and regulate indoor humidity. We’ll outline the different types of HVAC systems and when they’re most useful.



What Is HVAC?

The acronym HVAC stands for heating, ventilation, and air conditioning. It’s a collective term for all the different types of cooling and heating systems homeowners use to change the temperature and humidity indoors. HVAC systems also improve indoor air quality through mechanical ventilation and filtration. Some common HVAC systems include central air conditioning units, ductless mini-splits, furnaces, and boilers. HVAC also encompasses large-scale refrigeration in commercial buildings.



How Does HVAC Work?

Most commonly, HVAC systems are forced-air systems that provide heating and air conditioning as the air circulates through the system. Duct systems, such as central air conditioning, have a central unit that treats the air, and a blower that circulates treated air throughout a building’s ductwork and into the main living space.

Ductless systems like mini-splits do the same thing, but they exchange air directly with the living space instead of through ductwork. As the air passes through the HVAC unit, it may be run through air filters to remove allergens, dust, or other particles.



HVAC System Basics

HVAC systems contain many important components, including the following:

Air Ducts

A building’s ductwork is a system of tubing that runs throughout the walls and ceiling to carry warm or cool air from a central HVAC unit to multiple parts of the building. Ducts should be sealed and insulated to provide the highest energy efficiency. Air ducts are attached to air conditioner and heating units using special ductwork pieces called plenums. There are usually two plenums in a system: the supply plenum that handles outflow and the return plenum that handles inflow. 

Air Handlers

The air handler is the indoor portion of a central heating or cooling system that moves conditioned air throughout the building. It contains a blower motor and fan that sends heated or cooled air into the ductwork. The air handler also brings in air to be treated. In an AC unit, the air handler contains the evaporator coils that cool the air as it passes through.


The condenser is the outdoor unit of a central AC system. It acts as a heat exchanger for the refrigerant, a chemical used in ACs that produces a cooling effect when it expands or vaporizes. The condenser contains the condenser coils, which release heat from the refrigerant into the outside air, and the compressor, which prepares the refrigerant to return indoors and cool more air.

Humidifiers and Dehumidifiers

Depending on your local climate, the air in your home may need to be humidified or dehumidified to make your home comfortable and protect it from mold and mildew. Humidifiers add moisture to the air and dehumidifiers remove it. Air conditioning systems automatically dehumidify the air, but you’ll need to add a separate humidifier to your HVAC system in dry climates.


Refrigerant is a liquid that’s used to transfer heat from one place to another. In an air conditioner, it pulls heat from the indoor air and transfers it outside, cooling the indoor environment. Freon is one brand of refrigerant, but it’s sometimes used to refer to all refrigerants the way that Kleenex stands in for all facial tissue brands.


Most HVAC systems have a device for regulating the system’s function called a thermostat. The user sets the thermostat to their desired temperature, and the HVAC system works until temperature is reached and then turns off. This helps conserve energy and maintain a consistently comfortable environment.


An HVAC system’s vents connect the ductwork to a building’s interior or exterior. Vents serve many purposes, such as ensuring airflow and bringing in fresh air.

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Types of HVAC Systems

HVAC systems may provide heating, cooling, or both. Here are some of the most common systems you’ll find in homes today.

Air Conditioning

All air conditioners operate similarly: Blowing indoor air over tubes full of refrigerant to remove heat and humidity from the air. The heated refrigerant then travels to the outdoor part of the system, where it cools back down before returning indoors to start the process over. However, each system differs in how the components are packaged.

Central Air Conditioning

Central AC is a split system, requiring both an indoor air handler and an outdoor compressor. These are the most powerful and efficient types of air conditioners, but central air conditioners cost the most to install and run. They also require ductwork, so installing central AC if your home wasn’t built for it is expensive. However, in hot climates, central air goes a long way in making an entire home comfortable.


Mini-split systems also require an outdoor condenser and one or more indoor air handlers, but they don’t need ductwork. Instead, homeowners install an air handler in each room they wish to cool. Mini-splits are a great choice for cooling multiple rooms in an older house or one without existing ductwork. They’re also more customizable than central AC. Not everyone likes the look of an air handler unit mounted on the wall or ceiling, but there are ways to conceal them.

Other Air Conditioners

Non-split AC systems such as window units and portable air conditioners contain both the air handler and the condenser in the same housing. In a window unit, the condenser side faces outdoors to vent the heat, and the air handler faces indoors to distribute cool air. Portable air conditioners typically connect to the window via removable tubing, but can be packed up and put away during cooler months. These units only cool one room at a time, but they’re less expensive than permanent split systems and more affordable to run.


Boilers are somewhat uncommon HVAC equipment because they don’t blow forced air. Instead, boilers heat water, sometimes past its boiling point until it becomes steam, to send through a network of radiators throughout a building. The heated radiators then heat the air in each room. Boilers may run on natural gas including propane, heating oil, electricity, or even wood.


Furnaces burn fuel to warm air, which they then blow into a home’s ductwork for distribution throughout the house. Propane and natural gas furnaces are the most common and least expensive to operate, though some older homes in cold climates may still have furnaces that burn heating oil. These are powerful heaters, but they can produce toxic fumes such as carbon monoxide that must be properly vented.

Electric furnaces exist, but they take a lot of power and are slow to heat up, so they’re usually found in mild climates. Many mini-split systems can also act as electric furnaces.

Heat Pumps

A heat pump system transfers heat indoors in winter and outdoors in summer, providing both heating and cooling in one. These systems are highly efficient: An electric heat pump can heat your home with approximately 50% less electricity than a comparable furnace. However, they can be pricey to install, particularly if you choose a model that uses renewable resources such as geothermal energy.

Packaged Systems

Packaged systems combine heating and cooling equipment in a single housing that’s located outdoors. A heat pump with extra evaporator coils for cooling is one type of packaged system, and an air conditioner with added heat strips is another. These systems save indoor space by putting all the equipment outdoors, but they typically aren’t as powerful or efficient as other systems. Thus, they’re mostly used in small homes.

Radiant Heating

Radiant heating systems directly heat your home’s walls or floor, warming it without needing to circulate air. Most of these systems, called hydronic systems, use hot water or steam from a boiler to produce heat, but others may use electric heat cables. Radiant heating uses energy efficiently and reduces the circulation of allergens, but it’s difficult to install, particularly if your home wasn’t originally designed for it.



What Is the Difference Between HVAC and Air Conditioning?

Air conditioning is one type of HVAC system. Essentially, all air conditioners are HVAC systems, but not all HVAC systems are air conditioners. HVAC stands for heating, ventilation, and air conditioning, so it encompasses heating and ventilation systems such as furnaces, boilers, and heat pumps as well. However, many people use “HVAC” and “air conditioner” interchangeably, leading to confusion.



Professional vs. DIY HVAC Repairs and Maintenance

Hiring an HVAC technician is almost always best when repairing or maintaining your heater, air conditioner, or ductwork. Nearly all states require these technicians to maintain current licensure and complete training and apprenticeships to ensure they’re up-to-date on the latest technology. Few homeowners have the knowledge, expertise, or tools to work on HVAC systems themselves, as it’s a highly specialized field. You may be able to install a small window AC unit yourself, but you should always call a professional if you’re opening up or repairing your system.



Our Recommendation

There are a number of HVAC systems to choose from to heat, cool, and ventilate your home. The type of system that’s best for you depends on your surrounding climate and your home’s existing infrastructure. For example, if your area has brief, hot summers and your home has no ductwork, a mini-split system or window AC unit might be the right choice for cooling. We recommend contacting a local HVAC technician with any questions. They’ll be able to point you in the right direction whether you want to repair your system or install a new one.

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HVAC Systems FAQ

What does an HVAC system do?

HVAC systems provide heating, ventilation, and cooling for indoor environments. They typically circulate air in order to regulate the temperature and humidity within a building.

What is the difference between HVAC and AC?

AC, or air conditioning, is an indoor system that cools and dehumidifies the air. Air conditioning falls under the HVAC umbrella, but other types of heating and ventilation are also HVAC systems.

What are the four main types of HVAC systems?

While there are many types of HVAC systems, they usually fall into four categories.Split systems with indoor and outdoor units that provide both heating and cooling through ductwork.Hybrid split systems that allow you to switch between gas and electricity for heating.Ductless or mini-split systems that don’t require ductwork.Packaged heating and air conditioning that combine heating and cooling equipment in a single outdoor unit.