What Is an HVAC System and How Does It Work?

Most homeowners know what HVAC stands for (Heating, Ventilation, and Air Conditioning). Most also have a basic understanding of how the process works.

But very few people understand everything that goes into a full HVAC system.

This is understandable. How often do you have to think about your air conditioner, furnace, or another piece of HVAC equipment? Some have never had to purchase a new system, or do more than schedule routine maintenance for their existing equipment.

When it comes time to make a new investment, though, whether that’s building a new home or replacing existing equipment, it pays to know what’s what.

If you’re past that point and want to dig deeper into HVAC topics beyond this one, the Fire & Ice Learning Center is a great source for residential HVAC information. If you’re still getting a grasp on the industry, though, this article will act as a primer. By the end, you’ll have a solid understanding of HVAC equipment and processes, so that the conversations you have with your HVAC contractor are more productive.

What Is An HVAC System?

An HVAC system is the equipment, technology, and processes that go into heating, cooling, and ventilating a commercial or residential property. Typical equipment included in this definition includes air conditioners, heat pumps, furnaces, air handlers, ductwork, ventilation lines, filters, and other air quality products.

Let’s break down each of those for a more thorough understanding.

HVAC Equipment - Heating

Most homes will have a furnace heating their home. Furnaces come in different types and can use different fuel sources, including the following:

• Natural gas furnaces
• Electric furnaces
• Propane furnaces
• Oil furnaces
• Geothermal furnaces

Natural gas furnaces are the most common these days, although electric is more popular in some parts of the country where there are mild winters, the cost of gas is higher, or both.

Heating equipment generally includes a blower motor as well, which moves air throughout the home.

Most homes have what is known as a forced-air system. This is where the heat is distributed throughout the home through its ductwork by a blower.

HVAC Equipment - Ventilation

Ventilation includes any of the attached systems that help to process and move air throughout your home and HVAC system. This typically includes ductwork, floor, wall, and ceiling vents, and other ventilation shafts including chimney flues or PVC ventilation for indoor HVAC equipment.

A home’s ductwork is designed to house the air that is conditioned by the air conditioner or heated by the furnace. Inadequate ductwork can stifle a system’s ability to heat or cool, or may produce hot or cold spots where there isn't sufficient ductwork to carry the air.

Other ventilation such as chimney flues and PVC vents are often needed to vent excess heat from a system’s furnace.

Vents also exist on the outdoor air conditioning unit, and throughout the home to distribute air.

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Ductless HVAC systems will not include many of these more advanced forms of ventilation. There will still be an indoor and outdoor unit, and the indoor units (or “heads”) can often heat and cool (though some are cool-only). However, these are generally for an individual room or area, such as a finished basement or attic.

Many consider a home’s natural ventilation to be a part of this area as well. The ability to create cross-flow from windows and doors can be an important factor in keeping your home comfortable.

HVAC Equipment - Cooling

An HVAC system will traditionally include an air conditioner (or several of them for commercial properties). Additionally, heat pumps also work similarly to air conditioners. A heat pump can cool but can also heat a home.

Heat pumps are traditionally paired with electric furnaces, which supplement a heat pump’s ability to provide efficient heat. Air conditioners are traditionally paired with gas furnaces.

RELATED: Air Conditioner, Heat Pump, Furnace & Air Handler: What’s the Difference?

How Does An HVAC System Work?

The important thing to know is that HVAC equipment moves air. In general, a system exists to move warm air elsewhere, either into the home or out of it. A home’s air conditioner, heat pump, and furnace captures or creates the heat, then the blower and ductwork help to facilitate the movement.

Below we look at each sub-system and talk about specific equipment and processes. It’s important to remember that a central air HVAC system is a living, breathing system that functions as a whole. The heating system isn’t siloed off entirely from the cooling system, and the parts and processes that help both function properly often overlap.

Heating Your Home: How It Works

A furnace generates heat either through electrical energy or through burning its fuel source. This fuel source is most typically gas, but can be propane or oil as well.

A heat pump works somewhat differently when heating. It absorbs heat from the outdoor unit and transfers it to the inside. It’s not generating heat so much as transferring it from one place to another.

Cooling Your Home: How It Works

Instead of creating cold air, which is a common myth, air conditioners and heat pumps absorb heat from within a home and move it to the outdoor unit, where it is vented into the atmosphere.

The refrigerant in a cooling system is key to this. At different pressures, the refrigerant can be liquid or gaseous. The HVAC system modulates the pressures of the refrigerant depending on where it is. It is then able to absorb ambient heat and remove it once it’s at a different pressure.

By making the trip from inside to outside over and over, and with the refrigerant’s pressure modulating accordingly, heat is systematically removed from the home.

As mentioned earlier, a heat pump can do the reverse, absorbing heat from outside and transferring it inside. At very cold temperatures (freezing temps and lower), a heat pump will still be able to absorb heat from outside, but at a less efficient rate. This is why a heat pump is generally paired with an electric furnace, which has compatible technology and supplements the heat pump’s heating capabilities.

Ventilating Your Home: How It Works

Ductwork is the most obvious here, as it is directly connected to your heating and cooling system.

Ventilation for heating systems can also include chimney flue or vent stack for discharging excess heat. The efficiency of a furnace dictates what percentage of a furnace’s energy goes toward heating your home. Even in the most efficient heaters, though, which can hit 95-97% efficiency, the remainder is being vented.

Depending on the equipment, ventilation may need to be added that exits on the side of a home instead of above it. This is designed to prevent moisture condensation in the HVAC system itself, which can damage it long-term.

HVAC Odds & Ends

There are several ancillary items that we haven’t discussed yet, and large components of your equipment that help to regulate its function. Some of these are listed below, but this is not an exhaustive list of equipment within an HVAC system. Rather, the list is designed to give you a sense of what is part of a typical system, as well as a basic understanding of their function.

Air Return

An air return draws air into the main system through your filter.

Exhaust Outlets

We touched on some of these earlier when we talked about chimney flues and vent stacks, but exhaust outlets are any areas where heat is vented from the home.

Filters

Furnaces generally come standard with a 1-4 inch filter that traps particles that enter and pass through your system. These filters need to be cleaned or changed periodically.

Humidity Control Products

Dehumidifiers and humidifiers are often forgotten, but can be an important part of a whole-home HVAC system. They can lessen the burden on your heating and cooling equipment, making you more comfortable, healthy, and increasing your system’s efficiency.

RELATED: IAQ and You: Indoor Air Quality HVAC Products

Electrical Components

Each major piece of HVAC equipment needs to be able to relay information to other relevant areas of the system. This is particularly true when you have multi-speed equipment that adjusts automatically to the temperature. Proper electrical circuitry and controls manage all of this.

Thermostats

The thermostat is the endpoint for user control over the system, and relays instructions throughout the system. Depending on how complex your system is, and how much it needs to communicate with various devices, several electrical inputs may be needed in a thermostat.

Compressor

The compressor is a major part of an air conditioner or heat pump. It is what regulates the pressure of the refrigerant. Because it works a lot when your system is in use, the compressor requires routine maintenance to avoid breakdowns.

Coils

Coils absorb and transfer moisture and heat, and help to regulate the temperature of the refrigerant. The size of the coils can vary significantly depending on the efficiency of your unit.

Who Can Service HVAC Equipment?

Installing or servicing HVAC equipment requires years of training as well as state, local, and national certifications as required by your area. While some simple tasks such as filter changes can be performed by a homeowner, a licensed contractor should always handle repairs, part replacements, or full installations.

The number of skills required to install and maintain HVAC equipment is lengthy, and includes: plumbing, electrical work, metalwork, brazing (a form of welding), carpentry and others.

Additionally, many of the installation and testing processes require specialized equipment that a typical homeowner won’t own or have training on.

Learning About Your System: Only the Beginning

While a licensed HVAC contractor should perform work on your system, the more you know about it yourself, the better chance you’ll have of choosing the best system, options, and accessories for your home.

You’ll also be better prepared to choose the best HVAC contractor to meet your comfort needs.

While our Learning Center has myriad resources for every level of HVAC knowledge, if you’re looking for a good “next step,” check out our article on Top HVAC Questions below, which will continue you on the journey to becoming an HVAC expert.