What Is HVAC System And How Does It Work?

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Heating, ventilation, air conditioning – or HVAC – is a complex system that keeps your house comfortable. It includes heating units, cooling units, ducts, filters, fans, vents, and more. You’ll learn about each component of a HVAC system and how they work together.

What Is An HVAC System?

Most people know nothing about HVAC systems (see also ‘Seven Common HVAC Airflow Problems And How To Solve Them‘). Only a few people understand how these systems work. They need to be maintained regularly.

When it comes time to make an investment, whether that’d be building a new home or buying new equipment, it pays to understand what’s what when it comes to HVAC.

An HVAC system is a set of equipment, technologies, and processes used to heat, cool, and ventilate a building.

A typical example of an HVAC system is an air conditioning unit, furnace (see also ‘ How Does A Furnace Work? ‘), air handler, ductwork, ventilation line, filter, and other air quality products.

How Does An HVAC System Work?

Air conditioning systems capture or create heat, and then use fans and ducting to move the hot air away from people.

A central air conditioning system (see also ‘Central Air Conditioning Installation: How To Do It Yourself‘) is an integral part of any building. It helps maintain comfortable temperatures inside buildings by providing heat or cool air. It also regulates humidity levels.


Most homes will have a furnace that heats their home. They come in different types and use different fuels. Natural gas is the most common type of furnace today, but electric is also used.

Gas costs more than electricity, and oil is still used in some areas. Geothermal furnaces are becoming more popular as an alternative source of heat.

Forced-air systems use a blower motor to move air throughout the house. Heating equipment usually includes a blower motor, which moves air throughout your home.

Heating systems use electricity or natural gas to generate heat. Heat pumps transfer heat from outdoors to indoors.


Duct work is important because it helps to distribute warm or cool air evenly throughout the home. It also helps to prevent hot or cold spots.

Ventilation is important because it helps prevent mold growth and other problems. Chimneys and other vents help remove smoke and fumes from your house. Outdoor A/C units (see also ‘Should I Cover My A/C Unit In The Winter?‘) are used to cool down your home during hot weather.

Indoor units are used to warm up your home during cold weather. These types of vents are usually found in the attic or basement.

Natural ventilation is a major part of this area. Windows and doors allow air flow into the house. This helps cool down the house during summer months.

Ductwork is the most common type of ventilation. Chimney flues and vent stacks discharge heat. Efficiency of furnaces dictate how much heat is used.

Depending on the equipment, ventilation needs to be added that exits from the side of a house instead of above it. Ventilation systems should be installed to avoid moisture condensation inside the HVAC system.



An HVAC system includes an air conditioner or several of them for commercial buildings. Heat pumps also work similarly to traditional air conditioning systems. Heat pumps (see also our guide to heat pumps and emergency heat) can be used to both cool and heat a building.

Traditional air conditioning systems are typically paired with gas furnaces while heat pumps (see also ‘Which Is Better For Your Home: Heat Pump Vs Furnace?‘) are usually paired with electric furnaces.

Air conditioning systems cool or heat air inside your house by using electricity to move refrigerants around. A heat pump works similarly but uses an electric motor instead of refrigerant.

A furnace heats air using gas or oil. An air handler circulates warm air throughout the house.

Air conditioning systems use refrigerants to absorb heat from inside homes. Refrigerants are gasses that expand when heated, causing them to become less dense than air. This allows them to absorb heat from inside buildings. 

Once the refrigerant reaches a certain temperature, it changes phase from gas to liquid. When the refrigerant absorbs heat, it expands and causes the compressor to work harder. As the refrigerant cools down, it contracts and the compressor works less hard.

Heat pumps work by circulating cool air around your house. A heat pump uses electricity to make this happen. When you turn on your heat pump, it starts circulating cool air around your home.

You may notice that when you turn off your heat pump, the air gets warmer again. That’s because the heat pump was working hard to circulate cool air around your home, and now the air is getting hot again.

Things To Know

There are several ancillary devices that help regulate the function of the HVAC system. These include thermostats, humidifiers, air filters, and other things.

This list is not exhaustive, and there are many more devices that help regulate the operation of the HVAC systems.

Air returns draw air into the main system. Exhaust vents release heat out of the house. Furnaces come standard with a 1 to 4 inch filter that traps particles entering and passing through the system. Cleaning or changing filters regularly is important.

Humidity control products are often forgotten, but they can be an important part in a whole-home HVAC system.

They can lessen your burden on your heating and air conditioning equipment, making you comfier, healthier, and increasing your system’s efficiency.

A thermostat is an important part of any heating or cooling system. It manages the entire system by controlling the speed of fans, pumps, valves, and more. It also communicates with other parts of the system, including remote sensors.

Compressors are parts of air conditioning systems (see also ‘Top 10 Benefits Of Air Conditioning‘). They are used to regulate the pressure of the refrigerants. They work by absorbing and transferring moisture and heat. Their sizes can vary based on the efficiency of the system.

Servicing HVAC

Installing or servicing HVAC equipment requires years of training and certifications. A licensed contractor should always do the job. Some simple tasks such as filter change can be done by a homeowner.

But installing or servicing an HVAC system requires extensive knowledge about plumbing, electrical work, metals, carpentry, etc.

Specialized equipment is needed to install a security system. Homeowners should be trained on how to use this equipment.

A licensed HVAC contractor must complete an apprenticeship before being allowed to call himself a professional.

He or she must pass a test to prove he or she knows how to install, repair, and maintain heating and cooling systems. An HVAC contractor must be certified by the state to ensure his or her skills.


Hopefully this guide has helped you to learn what you needed to know about HVAC systems and how they work!

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