What is HVAC? | HVAC systems and how they work

Your HVAC system brings you indoor comfort all year long. (Did you just think, “Wait, they’ve lost me in the first sentence. What is HVAC?”🤔 You’re in the right place.)

Learn how HVAC systems work and what this fast-growing industry is all about.

What does HVAC mean?

HVAC (heating, ventilation and air conditioning) is the use of technology to treat air. HVAC is an umbrella term for the systems, equipment, manufacturers, contractors and technicians that:

What is HVAC used for?

HVAC makes indoor air feel more comfortable. HVAC systems boost the temperature, humidity and air quality of indoor living and gathering spaces.

An HVAC system also adds a buffer between a building and the elements. Without an HVAC system, the temperature inside a building would feel as hot, cold, humid or dry as the air outside.

Residential vs. commercial HVAC

Residential HVAC is the air treatment of homes, apartments, RVs and other living spaces. Smaller systems can heat and cool a single room, while a central system is designed for whole homes.

Commercial HVAC is for corporate offices, industrial buildings and retail stores. Commercial HVAC systems work like residential units, but they’re much bigger because they treat larger spaces.

HVAC: Heating

Heating systems warm indoor spaces. They either create or transfer heat at a central source, then distribute the heat throughout the space.

Furnaces are the most popular heating system in America. While heat pumps are less common, they are gaining popularity with the Inflation Reduction Act that drastically reduces the cost. Heating systems use a range of methods to deliver warm air to a room or building.

Heat distribution methods

Heat distribution methods make sure that warm air actually reaches the room it’s supposed to heat. Although forced air is the most common method in the U.S., there are options for spaces without ductwork.

Forced air heating

A forced air system uses a series of ducts and vents to deliver warm air. In a nutshell, here’s how it works:

Step 1️⃣: Supply vents pull indoor air into the forced air system.
Step 2️⃣: A central heating source, usually a furnace, heats the air.
Step 3️⃣: The warm air leaves the heat source and travels through a network of metal, tunnel-like structures called ducts.
Step 4️⃣: The air reaches a different set of vents. Return vents disperse the air back into the room.

Ductwork is commonly found in commercial spaces and most modern homes, which makes forced air heating so popular.

Radiant heat

Radiant heating systems use direct transfer to deliver warm air. The ceiling, walls or floors have a heat source beneath them. The heat source emits energy, warming the surrounding air on contact.

Radiant heat usually relies on an electric or gas-fueled source, such as a boiler, or a hydronic (water-based) fuel source like a water heater.

The heat source warms the steam, air or water-filled tubes under the floorboard. As a less invasive option, hot panels can be installed in the ceiling or walls.

Radiant heat is energy-efficient, but it’s less common due to its high installation costs.


Geothermal heating uses the ground as its heat source. A few feet under the earth’s surface, the ground absorbs the sun’s rays and keeps a near-constant temperature.

Pipes are buried in the ground, where they absorb the heat. The pipes carry the heat to a heat pump, which transfers the heat and distributes it.

Geothermal heat pumps are gaining popularity, since geothermal energy is considered a renewable resource. It’s expensive to install, though.

Heating systems

A heating system is a device that converts a heat source (or fuel) into warmth. Heating systems use a variety of methods to create or transfer energy.

Check out some of the most popular heating methods and how they work.



A furnace is the most common heating method in the U.S. Furnaces can convert gas, propane, oil or electricity into heat. 

Most furnaces are central HVAC systems, meaning they create heat in a single location and send the warm air through ducts.

Product Callouts Section

  • Did you know?
    The furnace was patented in 1919.

Product Pros Highlights

  • Low upfront cost
  • Great for extreme climates
  • Electric models are energy-efficient

Product Cons Highlights

  • High operating cost
  • Dry indoor air
Our top furnaces

Heat pumps

one ac unit next to a house

A heat pump is an air conditioning and heating system in one. Heat pumps come in gas and electricity-powered models.

Heat pumps don’t generate heat like a furnace. They transfer it. In heating mode, a heat pump pulls heat from the air, water or ground outdoors and brings it inside. 

In cooling mode, a heat pump works in reverse by pulling warm indoor air and transferring it outside.

Product Callouts Section

  • Did you know?
    Heat pumps are most commonly sold in North and South Carolina.

Product Pros Highlights

  • Energy-efficient
  • Low operating cost
  • Dual HVAC system

Product Cons Highlights

  • Not ideal in extreme climates
  • High unit cost
Our top heat pumps

HVAC: Ventilation

Ventilation introduces air into an indoor space. A strong ventilation system boosts indoor air quality and promotes even, consistent airflow.

  • Air purifiers clean and deodorize the air.
  • Humidifiers and dehumidifiers keep moisture at a safe, healthy level.
  • Fans and blowers keep air moving.

HVAC systems use a combination of natural and mechanical ventilation to keep air feeling healthy and comfortable.

Natural vs. mechanical ventilation

Natural ventilation is uncontrolled airflow. Think of the wind blowing or air moving through an open window or door. Indoor spaces rely on natural ventilation to add fresh oxygen to the air.

Mechanical ventilation is airflow controlled by equipment or a device. HVAC systems use fans, motors and blowers to move and disperse air.

Air filters

Forced air and central HVAC systems use air filters. Filters catch airborne germs, dirt, debris and even odors.

💡Tip: To boost indoor air quality, make sure your central HVAC system has the right size filter.

HVAC: Air conditioning

Air conditioning cools indoor spaces. 87% of American homes have air conditioning systems, making them more popular than furnaces and heat pumps.

Air conditioning units work by pulling heat and humidity from your home’s air. The heat is converted from gas to liquid and moved outside, cooling the indoor air.

Check out the different types of air conditioning systems.

Central air conditioning

Central AC is for whole-home cooling. To distribute air, central air conditioners use the same forced air system as furnaces.

A tunnel of ductwork moves the air, and vents disperse the air into each room. There are two common varieties of central air conditioners.

Split system

A split system air conditioner has an indoor unit (air handler) and an outdoor unit (condenser unit).

The outdoor unit collects heat. The indoor unit, or air handler, circulates the air and passes it through a filter.

Packaged system

A packaged system is also known as a local HVAC system. It operates in the same way as a split system, but all the parts are contained in a single outdoor unit.

The outdoor unit combines both elements of a split system in one. Some models of packaged air conditioners also double as heat pumps or furnaces.

Packaged systems are great for homes with limited indoor space. With no indoor unit, packaged systems are also quieter than split systems inside the home.

Mini split

Mini splits are ductless air conditioning systems. The outdoor and indoor unit connect through a set of wires, so it’s a great option for homes without ductwork or central HVAC.

An indoor unit, or the air handler, is mounted on the wall, ceiling or floor. The air handler adds cool air directly to the room.

Single-zone mini splits pair one outdoor unit to one indoor unit. For cooling a single room or an add-on to a home, they’re a cost-effective choice.

Multi-zone mini splits, or multi-splits, pair one single outdoor unit with multiple indoor units. You can individually adjust the temperature of each room (known as zoning).

Window unit

Window air conditioning is an affordable option for single-room cooling. Window units are electric, and most plug into a standard 115V outlet.

We recommend window units for apartment living and as supplemental cooling. Over time, window units have gotten quieter and more attractive.


What’s the difference between AC and HVAC?
AC, or cooling, is just one aspect of the HVAC industry. HVAC also includes heating and ventilation, which uses different systems like furnaces. All air conditioning systems are HVAC systems, but not all HVAC systems are air conditioners.
Where can I buy HVAC equipment?
You can buy central HVAC systems on the manufacturer website or through a local contractor. Some contractors have an exclusive deal with an HVAC manufacturer, so they sell only one brand’s products. Other contractors sell products from multiple HVAC brands. Mini splits and window units are available from third-party retailers like Amazon.
What is HVACR?
The R in HVACR stands for refrigeration, or keeping something cooler than ambient temperature. Refrigerant is the gas-to-liquid component in air conditioners, heat pumps and fridges.
What are the best HVAC brands?
Trane, Lennox and Carrier are considered elite HVAC manufacturers. High-quality, long-lasting products and strong brand recognition contribute to their high cost. Rheem, York and Amana have impressive catalogs, but are often less expensive than the elite brands.
How do I find a quality HVAC contractor?
If you’re starting the search for a contractor, get quotes from at least three businesses. Rates vary widely, even in the same location. Ask each contractor if they’re licensed to operate in your state. To verify, you can ask for a copy of their state license. The contractor should also be bonded and insured. If a technician is injured in your home, insurance covers the damages.

HVAC contractors near me

Need an HVAC contractor? Let’s help you skip the search. We’ve vetted hundreds of HVAC companies to find the best contractors and technicians in the U.S.

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