What Is an HVAC System?

Nearly every home in the United States has heating and air conditioning systems, commonly called HVAC systems. These systems are essential for regulating the temperature in your living space and keeping you and your family as comfortable and safe as possible. There are several different kinds of HVAC systems available for homeowners, and we’ll discuss all of these options and what components they include in this article.

We should note up-front that HVAC systems are complicated and require professional installation. Not only is the equipment expensive, costing you hundreds or thousands of dollars extra if you make a mistake with a DIY installation, but properly setting up the components is crucial for functionality. 

We strongly recommend checking out our list of the top-rated HVAC companies for information on choosing a highly-rated HVAC pro for your installation.

What Does HVAC Stand For?

HVAC stands for heating, ventilation, and air conditioning. The term refers to all equipment in your home that regulates temperature or indoor air quality. 

The below components should be included when referring to HVAC systems:

Heating

Heating systems are some of the most crucial parts of an HVAC system. They use furnaces, boilers, or heat pumps to produce heat for your home. Forced hot air (FHA) — also called forced air systems — and other heating systems that use blown air also use blower motors to help distribute the heated air through the ductwork behind your walls.

Ventilation

Ventilation is an often-forgotten portion of an HVAC system that provides clean, fresh air for your living space. HVAC systems use air filters to scrub pollen, dust, and other contaminants out of your air. Some use ultraviolet (UV) treatment to kill bacteria and pathogens, and systems equipped with dampers introduce fresh air from outside before heating or cooling it to prevent the air in your living space from getting stale. This is a form of natural ventilation, whereas indoor air purifiers and ventilation systems are considered mechanical ventilation. Dampers can also help control indoor humidity levels.

Air Conditioning

The air conditioning side of your HVAC system comes in handy in the warmer months, as it uses heat pumps or systems consisting of condensers, evaporators, and air handlers to cool and distribute conditioned air throughout your home. Many kinds of AC systems can be included in HVAC systems, including central air conditioning systems, ductless mini-splits, heat pumps, and geothermal air conditioners.

What Are the Different Types of HVAC Systems?

The term HVAC system refers to a system that controls your home’s temperature and air quality, but many types of cooling and heating equipment fall under this umbrella term.

Below is a list of the different types of HVAC systems and equipment, along with brief descriptions:

• Boilers: A boiler can use natural gas, oil, or propane to heat water inside a large tank or, rarely, electricity. The heated water is then passed to whatever portion of your heating system needs the hot water to provide heat to your home.
• Central AC: A central AC system uses evaporators and condensers to condition the air inside your home, along with air handling units that distribute the cool air evenly throughout your living space.
• Ductless mini-split systems: Contrary to its name, a ductless mini-split uses a small duct running through a single wall to connect an indoor AC unit to an outdoor unit for localized temperature control.
• Ductless multi-split systems: Some use this term to refer to a single compressor connected to multiple ductless mini-splits. The technology works similarly, but multi-split systems generally heat and cool an entire home rather than a single area.
• Forced air heating systems: Forced air heating systems pull cool air into the air returns in your system, warm it using a furnace or heat pump, and then push the heated air through the HVAC ductwork behind your walls and into your living space.
• Furnaces: A furnace is similar to a boiler in that it burns fossil fuels — or electricity, but rarely — to produce heat for your living space. However, furnaces heat air that is circulated in your home instead of heating water.
• Geothermal heating and cooling systems: Geothermal heating and cooling systems use heat exchangers and heat pumps to move heat to and from your home to a deep hole in the earth. Cool air can be transferred into your home in the summer, and warm air can be transferred to your home in the winter.
• Heat pumps: Heat pumps are convenient because they can provide heated air in the winter and cooled air in the summer. They use compressors and heat exchangers to condition the air inside your home. Heat pumps can be part of central AC systems, heating systems, and other options, like mini-splits.
• Packaged heating and air conditioning systems: A packaged HVAC unit includes all the components needed for heating and cooling in one package rather than having one unit inside and one outside or multiple separate units inside.
• Radiant heating systems: Radiant heating systems use boilers to heat water and circulators to move the heated water through pipes under your floors. The heat then radiates upward into your living space. Technically, baseboard heat and steam radiators also use radiant heat, so they are sometimes lumped into this type of system.

How Do HVAC Systems Work?

HVAC systems can work in various ways, depending on your system type. However, there are some key principles your system can use that are common among all the different HVAC system styles.

First, you have some fuel source. Depending on your system type, your fuel could be electricity, natural gas, oil, or propane. Your primary heating and cooling equipment uses that fuel source to heat or cool water or air for distribution throughout your home. Below are the three options for how your fuel is used:

• A boiler burns fossil fuels to heat water for baseboard heat, radiant heat, and steam radiators.
• A furnace burns fossil fuels to heat air for distribution through your home’s ductwork.
• A heat pump uses electricity to power a heat exchanger to remove heat from your home or heat air to be pushed into your home to regulate temperature. Heat pumps can be included in mini-splits, geothermal systems, and even central AC and heating systems.
• Condensers and evaporators in a central AC system remove heat from the air in your home and transfer it to the exterior.

Finally, a device distributes heat or cooled air throughout your living space. In the case of baseboard heat and radiant heat, water circulating pumps are used to move the heated water through the copper pipes. All systems that blow warm air throughout your home use blower motors to move the hot air through your ducts.

Components of an HVAC System

HVAC systems are complicated regardless of what kind you have and whether they provide heat alone or heating and cooling. Below, we’ll include a list of the common components of HVAC systems, along with brief descriptions of the purpose each one serves.

• Air ducts: Central HVAC systems that heat or cool air for your home rely on ductwork. Ducts run behind your walls and distribute air throughout your entire living space. Ductless systems technically do have a single duct, but it doesn’t function in the same way.
• Air filters and purifiers: All modern HVAC systems include filters to remove larger particles and contaminants from your air. Some include purifiers that expose the circulating air to UV light, others use electrostatic energy to pull contaminants out, and some pass air through carbon filters for filtration. Some of the best HVAC filtration systems use ionizers to add electrical ions to particles in the air to pull them out of suspension.
• Compressors and condensers: The compressor and condenser units create changes in pressure to convert your refrigerant from a liquid to a gas and back. In a central AC system, the condenser is the unit that sits outside, while the compressor is usually located in your indoor unit.
• Evaporator coils: Evaporator coils are located on your indoor air conditioning unit. As the refrigerant flows through the coils, it absorbs heat from the air around them. The cooled air can then be blown into your living space.
• Fans and blowers: HVAC systems that condition air use blower motors attached to fans to push the heated or cooled air into your home.
• Heat exchangers: Heat exchangers are made of metal with high thermal conductivity. As air is blown over them, the heat inside the exchanger quickly heats it for distribution. Some high-efficiency heating systems use a double heat exchanger to recapture heat normally lost to exhaust.
• Refrigerant lines: Refrigerant lines are used in central AC systems, carrying Freon or, more commonly now, Puron. The refrigerant in your air conditioning system transitions back and forth from a gas to a liquid, and the chemical change releases or absorbs heat depending on where the transition occurs.
• Returns and supplies: Two key parts of your HVAC ductwork are the returns — which pull air from your living space for conditioning — and the supplies — which deliver conditioned air from your system throughout your living space. Returns and supplies are the connections between your living area and your ductwork.
• Thermostats and controls: The thermostat in your home controls how often your HVAC equipment is called upon for heating or cooling. Some homes have multiple HVAC zones and, therefore, multiple thermostats. Mini-splits often have stand-alone control systems, like a remote, to control the temperature.

Energy Efficiency of HVAC Systems

When you’re thinking about purchasing a new HVAC system or replacing an old one, the energy efficiency of your equipment is one of the first things you should consider. There are two efficiency ratings to consider regarding heating and cooling equipment.

Heating systems use a measurement of efficiency called the annual fuel utilization efficiency, or AFUE for short. Your AFUE rating is a percentage that tells you how much of the fuel — natural gas, oil, or propane — that’s burned gets converted into heat for your home. High-efficiency furnaces can sometimes reach 99% efficiency. These will be expensive, but they often pay for themselves, given the high cost of fossil fuels for home heating.

HVAC Brand Reviews

With the wide variety of air conditioning systems and numerous brands available, reading reviews is crucial to finding the best AC unit for your home's needs and budget.

Central air conditioners, ductless mini splits, portable ACs, and other types all come in a range of models with different features, capacities, efficiency ratings, and more. Prices can vary widely as well, from a few hundred to several thousand dollars depending on the brand, size, and technology.

Reviews from experts and homeowners can provide valuable insight on how certain AC models stack up in terms of reliability, noise levels, sizing accuracy, energy efficiency, and overall value. They can also highlight potential downsides to be aware of.

Be sure to research reviews of the top brands' latest AC model lines before investing in a new system. Focus on reviews of central air conditioner systems or ductless mini splits rather than window units. Key aspects to look for in AC reviews include:

• Noise ratings - How quiet is the indoor and outdoor unit?
• Sizing accuracy - Does the BTU capacity match as advertised?
• Efficiency - How does the tested SEER rating compare to claims?
• Reliability - Are there issues with breakdowns or needing repairs?
• Warranties - Does the company stand behind the AC with a solid warranty?
• Cost - Does the performance and durability justify the price tag?

In addition to reviews, be sure to compare warranties when choosing an AC brand. Reputable companies will back up their air conditioners with at least 10 years of coverage on major components.

For the latest reviews on top-rated air conditioner models across different types and brands, check out our Air Conditioner Reviews subcategory page.

Maintaining an HVAC System

HVAC systems are complex and have quite a few moving parts. While they’re built to last for 15 to 20 years, on average, you can extend that lifespan by performing routine preventative maintenance on your equipment. Below, we’ll list some of the most crucial things you can do to keep your system running properly.

• Replace your air filters at least once in the fall (for heating) and once in the spring (for cooling) to maintain good airflow.
• Make sure the area around your condenser unit outside is overgrown or crowded.
• Set your thermostat to COOL in the spring and HEAT in the fall.
• Make sure you don’t have furniture or other belongings blocking the returns or the air supply vents throughout your living space.
• Use a programmable thermostat to reduce unnecessary wear on your system.

Lastly, we strongly recommend hiring a reliable professional HVAC company to perform preventative maintenance or a tune-up at least once yearly. This will help ensure your system’s moving parts are working properly and that there’s no minor damage to your components that could lead to more severe issues if left unchecked.

Additionally, call in an HVAC technician at the first sign of any issues. These include your system making strange noises, your AC blowing warm air, or your unit not turning off. These problems all indicate serious issues that will only get more costly to repair the longer they go without professional service.

Learn More About HVAC Costs

Learn what different components of your HVAC system will cost to repair or replace.