What is an HVAC System and How Does It Work? What You Need To Know

HVAC systems are essential for homes across the United States. However, not all of them are equal.

They are many varieties that fulfill the needs of different homes and climates.

Keep reading to learn all about the different types of HVAC systems, how they work, and which ones you should use for your home.

Outdoor units of an HVAC system

What is an HVAC System?

HVAC systems are a staple in millions of homes around the world. The HVAC acronym refers to heating (H), ventilation (V), and air conditioning (AC) systems. 

The term encompasses various heating and cooling systems, including furnaces, air conditioners, fireplaces, and ventilation systems. An HVAC system can be any of the following:

Furnace

a person adjusting the furnace

A furnace is a system composed of four primary components, including:

  • Burners – deliver and burn fuel
  • Heat exchangers – absorb heat from the burning fuel
  • A blower – blows air across the heat exchanger to warm the air
  • A flue – eliminate gaseous by-products and exhausts outdoors

The system generates heat by using and burning fuel, then distributes generated heat throughout your home via your ductwork.

There are two main types of furnaces: gas and electric. Electric furnaces are often paired with heat pumps, while gas furnaces usually accompany air conditioners. 

Central Air Conditioner

Central air conditioners work as a ducted system that efficiently cools your home via an outdoor unit, an indoor unit, and ductwork throughout your home. 

The system pulls heat energy out of your home and transfers it to the outside air. These systems are common in homes with pre-existing ductwork. 

Heat Pump

diagram of how a heat pump works

Heat pumps are a popular, energy-efficient choice in homes in mild climate zones. Although many people assume the system is specifically for heating, it is capable of both heating and cooling. 

The system works like an air conditioner and has the same components. In the summer, heat pumps remove heat from your home. 

And in the winter, they add heat to your home. They “exchange” heat from one area to the other with compressed refrigerant gas, which absorbs and releases heat. The compressed gas flows back and forth between the indoor and outdoor units. 

Although they can heat and cool, heat pumps are often supplemented with electric furnaces. The electric furnace adds extra heat if it ever gets too cold for the heat pump to work effectively.  

Ductless Mini-Split Heat Pump

a ductless mini-split next to an HVAC

Ductless systems, including mini-split heat pumps, are popular choices in homes and apartments without existing ductwork. Since ductwork installation requires considerable renovation, ductless systems are a great alternative. 

These systems work best for heating or cooling a single room or “zone” in your home. They work similar to central air conditioners and ducted heat pumps, as they have an indoor and an outdoor unit. 

But, instead of distributing the heated or cooled air throughout your home, it goes directly into your room with the indoor unit. Since ductless mini-splits skip the ductwork, they are much more efficient than ducted systems. 

Other Options

Besides the popular HVAC systems, there are a few more options for heating and cooling your home. A few of these alternative options include:

  • Geothermal heat pumps: Also known as ground source heat pumps; these units are highly effective for heating and cooling your home. They extract heat from the ground, where the temperature is stable and constant. 
  • Window AC units: Window air conditioners simply consist of a single unit with everything in one box. The units are usually mounted or installed in a window and pull power from a traditional electrical outlet. 
  • Portable AC units: Portable air conditioners, as the name implies, can easily be moved from room to room. They require venting via a window or a wall, generally achieved with an exhaust hose. Think of them as a window AC unit with wheels on your floor. 
  • Fireplaces: Gas and electric fireplaces are other options for heating your home. Depending on your choice, the fireplace will generate heat via electricity or gas.
  • Whole-house fans: These are installed in the ceiling between the attic and living space. The fan pulls air through your home, venting out the attic while bringing fresh air from open windows. 

How Does an HVAC System Work?

Most HVAC systems do the same thing, but they work differently.

HVAC For Heating

HVAC expert checking the HVAC’s furnace

There are a few different HVAC systems that can effectively heat your home. Generally, homeowners use a furnace or a heat pump to achieve a warm, comfy environment. 

Furnaces

If your home has a furnace for heat, it either uses electrical energy or burns a fuel source. Generally, furnaces burn natural gas, but some models use propane or oil instead.

Pros

  • Inexpensive to install 
  • Reliable heat, even in extreme cold
  • Require less maintenance than other heating options

Cons

  • Electric furnaces can be pricey to run 
  • Gas furnaces have a shorter lifespan than electric options
  • Can pose hazardous risks (gas)

Heat Pumps

A heat pump works differently than a furnace to generate heat. It technically doesn’t generate its heat. Instead, it absorbs heat from the outdoors then transfers the heat indoors, thus heating the house. 

This heat exchange from outdoors to indoors is possible with the vapor-compression refrigeration cycle. Even in cold weather, outdoor air holds some heat that a heat pump can capture and use to warm up your house. 

Pros

  • Highly efficient
  • Lower running costs
  • Superior air quality
  • Quiet operation

Cons

  • High upfront cost
  • Less efficient in extremely cold weather
  • May require an electric furnace, fireplace, or space heater in extreme cold

HVAC For Cooling

technician checking an HVAC system

To cool your home, you can use various HVAC systems. The primary picks for efficiently cooling homes are air conditioners and heat pumps. The way these two devices cool your home is pretty much the same. 

Both units use refrigerant, a critical element in the cooling system. The refrigerant changes between liquid or gaseous, depending on the stage in the vapor-compression refrigeration cycle. 

Your HVAC system regulates the pressures of the refrigerant depending on where it is in the system. The indoor unit absorbs ambient heat from the air, cooling it. Then, the refrigerant flows to the outdoor unit, and its pressure drops. It then releases the heat outdoors. 

The system cycles, making the trip from inside to out repeatedly. As the refrigerant’s pressure adjusts and the refrigerant flows, the system efficiently removes heat from your home. 

Again, heat pumps and AC units use this same process to cool your home. But, heat pumps can also work in reverse, bringing heat from outside to inside during cooler temperatures. 

Note: Given the similarity of the two systems, they share many pros and cons. The upfront installation of each can be expensive. But both options are highly efficient, translating to lower running costs. 

HVAC For Ventilation

a person adding ventilation in the ductwork.

Ventilation is a key part of many HVAC systems, especially central air conditioners, heat pumps, and gas furnaces. 

A key component in central heating and cooling systems is ductwork. It is what transfers the heated or cooled air throughout your home from its direct connection to the system.

In addition, chimney flues and vent stacks can also be part of the ventilation system. These components affect furnaces because they require somewhere to discharge excess heat and exhaust dangerous gasses. 

Note: Ventilation that exits on the side of the home instead of on top of it may be required for certain HVAC equipment. The purpose of this is to prevent moisture condensation from draining back into the system itself, which can damage it in the long run. 

Parts of an HVAC System

HVAC systems consist of various components, each working in tandem with the others to reach the overall goal. Depending on the system in question, some components in our list below may not be present. 

Ductwork

a worker installing ductwork

The ductwork in your HVAC system is critical for dispersing heated or cooled air throughout your home. Many new houses incorporate ductwork from the get-go, which simplifies the process of integrating central heating and cooling. 

Note: Installing ductwork is expensive. 

The ductwork connects to the system itself, transporting air from the HVAC system to various parts of your home. Generally, the ducts are metal or synthetic, insulated tubes.

Air Return and Supply Vents

an air return vent on the ceiling

The air return and supply vents are also key components in your HVAC system. 

Supply vents are located on your floor and supply cooled or heated air into the rooms of your home. They connect to your HVAC unit via ductwork. 

On the other hand, return vents allow air in your home to return to the system for heating or cooling purposes. These vents are usually on your walls near your ceiling. It draws the air from your home into the main system through the filter. 

Note: Return and supply vents are essential for maintaining a consistent, comfortable temperature in your home. 

Furnace Exhaust Vents

These vents are any outlet areas where heat is vented from your home. We mentioned chimney flues and vent stacks earlier on, which are types of exhaust outlets. 

Exhaust fans remove odors, moisture, and fumes from a particular area of your home. The fans then propel the air out of your home via the vents. 

Air Filters

a man installing a new air filter

The air filter in your HVAC system is important for optimal system function and maintaining clean, healthy air. Air pulled from your home moves through the air filter as it goes through the system. The filter removes dust, pet dander, pollen, pathogens, and other small particles from the air. 

HVAC systems typically have standard 1-4 inch thick filters that capture particles passing through the system. Some systems have multiple filters to help purify the air. Your HVAC unit may have a MERV or HEPA filter, depending on the brand. 

In addition, some manufacturers incorporate air purifying technology, like UV lights, to help eliminate dangerous particles like airborne pathogens. 

Humidifiers and dehumidifiers 

When we think of HVAC systems, many of us fail to realize that humidifiers and dehumidifiers have their place in the system as well. Besides cooling and heating, many HVAC systems have dehumidifying or humidifying capabilities. 

In scenarios where the air in the house is too dry, the system may add humidity to bring the air in your home to the correct humidity level. On the other hand, in humid climates, the dehumidifier may work overtime to keep your home comfortable and dry. 

These two additions can be a vital part of the entire system as they lessen the burden on the equipment. 

Thermostats

a technician installing a thermostat

The thermostat in your home is the helm of your temperature control over the HVAC system. It communicates your adjustments throughout the system, telling the components what to do and when. 

If your system is highly complex and needs to communicate with various devices, multiple electrical inputs may be necessary. Some HVAC systems have smart thermostats that allow optimized control (sometimes even wireless remote control), especially highly efficient, industry-leading models.

Electrical Components 

While the thermostat is the face of the electrical aspect of your system, the control board, on the other hand, works behind the scenes to keep everything running smoothly.

Note: Every component of your HVAC system needs to effectively communicate information with other parts of the system. 

If you have a multi-speed or variable speed unit, this becomes especially important, as the system adjusts automatically to the temperature. The electrical circuitry and controls manage the entirety of this aspect of your HVAC equipment. 

Blower 

The blower in your HVAC equipment does what it exactly sounds like: it blows heated or cooled air through the ducts and into your home. You may also hear it referred to as “blower motor.”

The blower motor is responsible for forcing the conditioned air through the duct system and out of the vents in rooms throughout your house. 

Compressor 

a technician checking the compressor’s amp

The compressor is the heart of the system in heat pumps and air conditioning units. Its function is to pump and regulate the pressure of the refrigerant, which, as we’ve learned, is a critical part of conditioning the air. 

Since it plays such a major role in the system and constantly operates while the system is in use, it’s prone to breakdowns and requires routine maintenance to avoid issues. 

Evaporator and Condenser Coils

In heat pumps and AC units, you’ll find evaporator and condenser coils. They each handle different sides of the cooling cycle. The evaporator coil handles removing heat and moisture from indoor air to bring its temperature down. 

On the other hand, the condenser coil takes the heat and releases it outside. 

The coils are responsible for absorbing and transferring heat. The coils may fluctuate dramatically in size depending on the system’s efficiency.

Outdoor Unit

outdoor unit of HVAC

Heat pumps and air conditioning units (except portable and window units) have an outdoor and an indoor unit. The outdoor unit is often the first thing that comes to mind when we think of the physical HVAC system, as it’s usually in plain sight. 

Inside the outdoor unit, you’ll find the fan, which provides airflow, and the compressor and condenser coil. This is where heat from inside your home disperses. 

Indoor Unit

The indoor unit of your HVAC system is responsible for cooling the air. It draws the heat and removes moisture from the air inside your home. The indoor unit holds the evaporator coils and a filter. 

While only certain HVAC systems have an outdoor unit, they all have an indoor unit. Whether it’s a furnace, mini-split heat pump, portable air conditioner, or central AC unit, they all have one. 

Of course, the indoor unit’s function looks different from the furnace since it’s heating the air. However, there isn’t a difference between the general function of the furnace and the “indoor unit” since the system doesn’t have an outdoor portion. 

Burner 

The gas furnace’s burner is the portion where the fuel mixes with air and is burned. Depending on the type of furnace you have, it may run using gas, oil, or even propane.

Heat Exchanger

The heat exchanger in a gas furnace is a thin metal barrier situated between the blower and combustion chamber. It separates the combustion process from your breathing air. 

Note: The separation is critical because the combustion process produces a toxic byproduct. 

Flue

Gas furnaces require a flue, which escorts combustion gasses safely out of your home. The flue usually feeds through your home and up through the roof, where it expels gasses above the roofline.

How Much Does an HVAC System Cost?

a house builder putting ductwork for HVAC

HVAC systems range in cost depending on a variety of scenarios. For example, the size of your home, quality of the ductwork (if applicable), your local climate, and the brand you choose all impact the final cost of the system. 

The chart below offers a general idea of average costs for each system type. Due to major variations of different homes, your costs may be higher or lower than those listed in the chart. 

Type Of EquipmentInstalled Cost
Electric Furnace$2,000 to $7,000
Gas Furnace$3,800 to $10,000
Central Air Conditioner$2,500 to $7,800
Heat Pump$3,800 to $10,000
Ductless Mini-Split Heat Pump$1,800 to $10,000
Window Air Conditioner$150 to $800

The drastic fluctuation in cost is due to the wide variety of scenarios. For example, central air conditioners come in multiple sizes, ranging from 1.5 tons to 5 tons. 

Depending on the size of your home, you may only need a 1.5-ton unit. Or, on the flip side, maybe you need a 5-ton unit. The cost difference between the two is significant, not to mention the other factors that directly impact the overall cost of the system. 

Check out our guide on calculating the right size AC unit for your home if you’d like to learn about this. 

HVAC Maintenance Costs

a repairman checking the HVAC system

Maintaining your HVAC system is essential for prolonging its lifespan. Depending on the system in question, maintenance may include the following:

  • Cleaning of drains, coils, and elements
  • Monitoring refrigerant pressure
  • Lubricating moving parts
  • Testing safety controls
  • Inspecting connections, thermostat functionality, and motor operations

The chart below reviews the average annual maintenance costs for each system type. Of course, the final maintenance cost may be higher or lower depending on whether repairs are necessary. However, the chart offers a general overview of average costs.

Type of EquipmentAnnual Maintenance Cost
Electric Furnace$150 to $500
Gas Furnace$50 to $300
Central Air Conditioner$100 to $500
Heat Pump$150 to $650
Ductless Mini-Split Heat Pump$100 to $600, depending on the number of indoor units
Window Air Conditioner$75 to $200

What is the difference between AC and HVAC?

The difference between AC and HVAC is what the acronym refers to. HVAC encompasses heating, ventilation, and air conditioning. On the other hand, AC simply refers to air conditioning. 

So, if you see ‘AC’ in reference to an HVAC system, it’s specifically referring to an air conditioning system. If you see ‘HVAC,’ it could be referring to any system under the general umbrella. 

Related Article: Common Air Conditioner Problems

Learn More About Your System

Learning the general overview of your system is only the tip of the iceberg. When it comes to deciding which HVAC system(s) is best for your home, there are several more things to keep in mind. For example, efficiency, ratings, and sizing are all important factors to consider. 

However, now that you have the general groundwork of knowledge laid out, learning about other aspects of your system will be much easier.

About The Author

Jonathon is a mechanical engineer with over ten years of experience in the HVAC industry. He has hands-on experience with all types of HVAC systems.

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