HVAC System Components: How Do They Function?

HVAC system components are handy and sometimes even vital to know about, whether you are homeowner trying to find a problem somewhere in your HVAC system or an apprentice HVAC technician learning the basics of HVAC systems and the HVAC system working principles.

Being able to maintain your HVAC system, detect when and where problems arise and prevent them from becoming worse is a major benefit to understanding your HVAC system components. You can save yourself money by looking after your system properly and preventing it from suffering from damage over time or outright breaking down.

The main HVAC system components to be aware of are the:

Need help with a repair or install? Get a free estimate online from top local home service pros in your area.

Furnace Central Heating

The furnace is the main source of heat for most households which have a central heating system. Usually it’s those of you who live up in the colder northern and eastern states and suffer harsh winters. Those in warmer states usually just have the cooling part of a HVAC system and use zonal heating such as a fireplace or wood stove for when they need it.

Whether you use a wood burning, oil or gas furnace, it is split into three major components that contribute to it functioning as one of the HVAC system components.

Heat Exchanger

The heat exchanger is where the main transfer of heat from the furnace occurs. It functions to expose cool air from your home to the heat generated by the furnace combustion chamber when prompted by your thermostat. The newly warmed air is then transferred to your home via your ductwork.

Some furnaces have an extra duct that allows the cool air to enter the heat exchanger at a quicker rate, essentially allowing your home to warm up quicker. The heat exchanger itself is a very resilient component made from stainless steel with alloys giving it resistance to damage from high temperatures.

If your heat exchanger was to suffer damage to its structure, such as cracks or holes formed after denting, it can be a serious cause of concern. Carbon monoxide can escape and enter your home which is a gas which has no color or odor and cause symptoms that range from dizziness, headaches, nausea, drowsiness and death.

If you have a furnace at home, be safe and secure by using a carbon monoxide detector which can be cheaply and easily found on Amazon such as the First Alert Carbon Monoxide Detector Alarm. If you do suspect a carbon monoxide leak, call a professional HVAC technician or gas engineer immediately.

Combustion Chamber

The combustion chamber is where the fuel is mixed with oxygen added (via a diversion in the return duct) and combined with a source of ignition to generate heat energy. In gas furnaces the source of ignition is the pilot light whereas other furnace types most typically use electronic ignition.

In oil burning furnaces, the oil needs to have air introduced to it to become vaporized. Once a vapor it can then reach the source of ignition to be combusted. If the vaporization process has a fault, the combustion chamber can become flooded, collapse and will need replacing.

You can get open or sealed combustion chambers. Open are more common and less costly but closed combustion chambers are generally safer and more efficient as carbon monoxide and uncombusted fuel can be captured and relit

Combustion chambers are also known as burners.

Blower Motor

Once the air that has entered the furnace has reached the temperature dictated by the thermostat, the blower motor kicks into action and pumps this air through your ventilation system to be dispersed throughout your home.

The blower continues throughout the heating cycle and after combustion ends so that all of the warm air produced is blown throughout your home. This is the element you can hear at work the loudest and so you will notice when i kicks in and goes off again.

There are different variations of blower motors but the best are the variable speed ones which adapt the speed of the blower to adjust the force of air flow around your home. This can compensate for certain HVAC system problems which relate to air circumvention.

Need help with a repair or install? Get a free estimate online from top local home service pros in your area.

AC Central Cooling

Central cooling systems are perfect for homes located in hot and humid states. They also make great HVAC system components for homes in colder climates still because they work with the rest of the system to modulate the air temperature to get it perfectly comfortable for you.

The workings of an air conditioner unit corresponds to the refrigeration cycle in which a refrigerant chemical is evaporated and condensed in a closed system to transfer heat from the air of the room to the air outside. The main components of an AC unit are as follows:

The Refrigerant

The refrigerant is a chemical used for its stability, non-flammability and its ability to change from liquid to gas and back again with ease. A refrigerant is usually a CFC (chlorofluorocarbon) which work extremely well for the vapor compression refrigeration system but they are toxic to the environment.

Historically in older refrigeration cycles, such as the vapour absorption refrigeration system, ammonia was used, but this format was inefficient and has a low coefficient performance when compared to the newer model.

The Refrigerant Loop

The loop is the system of pipes that the refrigerant travels through between the various components of the AC system.

Damage to the loop can cause a refrigerant leak and this can result in an ice build up on the other components, reducing their efficiency and even causing a need for repairs or replacement.


A compressor is responsible for mechanically compressing the refrigerant, greatly raising its pressure and its temperature. As heat is more inclined to travel from a high pressure to a low pressure environment, this has prepared the refrigerant for exhausting the heat it will pick up in the next component; the condenser.

The compressor consumes the most power out of all of the AC components and is regarded as the “heart” of an AC unit as it drives the refrigerant through the system.


After leaving the compressor and upon entering the condenser the refrigerant is in a vaporous state. This is a state of matter between gas and liquid.

The condenser contains many coils which the hot, high pressure refrigerant will travel through and comparatively cool, low pressure air from the outside is blown across.

The coils serve to increase the surface area to facilitate the transfer of heat energy from the refrigerant to the outside air. The heated air is then exhausted outside. The refrigerant has now cooled slightly and has changed into a liquid state but still remains quite high in temperature.

The condenser coils are located on the outdoor portion of your cooling unit and since it is exposed to the outside, it needs to be protected and maintained. Try to keep debris and dirt from entering the system while making sure to use AC coil cleaners to prevent the build up of debris on the coils.

Expansion Device

The hot, high pressure liquid refrigerant will enter the expansion device after the condenser which acts to dramatically decrease the pressure and the temperature of the refrigerant. The refrigerant will then leave as a cool liquid and travel to the evaporator.


Just like the condenser, the evaporator contains many coils for the refrigerant to travel through which increases the surface area for the transfer of heat energy. This time, the refrigerant is low in pressure and the fan is blowing in air from the room.

The high pressure, hot room air has its heat energy transferred into the refrigerant and the newly cooled air is ejected back into the room. The refrigerant, now containing heat absorbed from your indoor air, goes back into a vaporous state and begins the cycle again, travelling through the compressor towards the condenser to exhaust the heat it has absorbed.

Even air form the inside of your home will contain dust, debris and dander which can build up on the coils reducing the overall performance of the cooling system and shortening its lifespan. Make sure to clean the coils now and again.


The ventilation is pretty simple and does not have a whole host of components to remember. The main problem to looks out for with ventilation is blockages or damage which can disrupt or impair airflow throughout the home.

Air Filters and Dust Collectors

While not being required components for a functioning ventilation system they are without a doubt essential to have. Air filters and dust collectors grab the particulates out of the air and keep them from being dispersed through your home.

They are vital because they help to protect your health and keep the air that your breathe clean. Some air filters have a electrostatically charged pleats which trap the smallest microbes, such as bacteria and fungi which can cause respiratory illness.

While air filters just slot into your ductwork, dust collectors are larger pieces of machinery that actively extracts particulates from the air. These are more suited for use on building sites or in workshops than in a home.


Fans can be used in larger HVAC systems that have extensive ductwork running throughout the building. They serve to adjust the airflow and keep it optimal. If you have a large house and find that your HVAC system components are not performing to the highest quality, perhaps air pressure is just too low in the ductwork.

Fans are also used on a more commercial basis and are rarely used in residential ductwork. In some cases, exhaust fans are used, in the kitchen for example, to stop smoke and condensation build up in a busy kitchen that has low ventilation.

The Thermostat

The thermostat is the temperature control panel for your other HVAC system components which is set and determined by you. The thermostat has temperature sensors which dictate to the other components when they should be turned on and off to begin and end heating and cooling cycles.

Thermostats are best kept in the centre of the house away from drafty or cold areas to obtain accurate temperature readings. Sometimes you can have multiple thermostats that control individual components, or separate portions of the house, depending on the set up you have.

Some thermostats also have timer settings allowing you to schedule your heating or cooling. You may wish to set it to kick in the heating or cooling about 30 minutes before you come home from work, giving you the convenience of making sure your home is comfortable.

Need help with a repair or install? Get a free estimate online from top local home service pros in your area.

About the Author

Dave Miller is a HVAC technician with over 10 years in the industry. Dave created HeatTalk with the ambition for it to become a resource for individuals looking for answers, whether they be a layman, student or a professional.

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