How Does HVAC Work?

You’ve got the papers signed, the inspections completed, the moving trucks all set up. It’s official: you’re a homeowner. Congratulations!

You’ve spent hours picking out the exact shade of white to paint the living room (eggshell? Alabaster? Parchment, definitely parchment) and you’re so excited to break in your new couch this weekend with your housewarming party.

But as soon as you step foot in the door, you decide to turn up the air conditioning. Going to your basement, you glance at the machine and...feel a sense of dread. That collection of metal tubes and boxes looks like it comes from another planet. You know it’s the HVAC unit but you have no idea how to use it, which leads you to wonder...

How does HVAC work?

Here in Denver, we at TJ Christensen’s Heating & Cooling field this question regularly. So let us help you, you curious and responsible homeowner, understand our favorite part of your house: the HVAC unit.

What Does "HVAC" Mean?

But before we get into how HVAC works, we need to learn the meaning of those four letters.

  • Heating:

    • Forced air: furnace heating systems consist of a burner, heat exchanger, blower, and a flue. The burner turns on when thermostat needs to be heated and signals the fuel exchanger to start the heating process. The exchanger absorbs air and turns the fuel and air mixture into heat, which will be sent via ductwork back into your home. Blowers move air through ducts and into different parts of your home.
    • Boiler: water is heated in boilers. From there, it’s distributed from piping to radiators in different rooms of your house to ensure equal heating.
    • Electric baseboards: heating elements in floors that heat up when the thermostat calls for heat - some have a blower to distribute heat.
  • Ventilation:

    • Flue and vent pipes: fresh air helps bring heated air to correct temperature before being distributed throughout the house. The flue and vent pipe are important to keep air in the house safe to breathe. They exhaust harmful byproducts of combustion (carbon monoxide and other noxious fumes) and push them outside of the building. The flue opens and closes to be sure there are no backups of dangerous exhaust. 

  • Air Conditioning:

    • Air conditioners are made of:
      • Outdoor unit with compressor, fan, condenser coil, and electrical components
      • Evaporator coil (on top of furnace)
      • Piping (connects indoor and outdoor components)
      • Refrigerant for cooling
      • Ductwork for air distribution
      • Thermostat
    • When needed, the air conditioner pulls warm air from the home into ductwork. At the same time, refrigerant circulates between indoor and outdoor components. It absorbs heat from the air as it passes into interior evaporator coil from exterior compressor coil. The cooled air travels back through ductwork and is distributed through the home.

Phew, so now that you know the meaning of the letters, let’s get into the different mechanical parts of the HVAC system.

Intro to the Parts of the HVAC System

There are multiple parts of your HVAC system, some you already may be familiar with! Here are the major ones:

  • Thermostat:

    • Thermostats are the tools (usually either a plastic ring set on your wall that allows you to set the temperature to what you’re looking for, or it’s a computer that you can set). The temperature can be set manually at any point day or night, or it can be set automatically to keep your house at a specific temperature. When it gets too hot or cold, the thermostat triggers HVAC to start circulating air as needed.

  • Heating System:

    •  Home heating is typically achieved by either a furnace or boiler, both of which use different methods for making sure you and your loved ones stay happy and warm (or cool) on a daily basis.  

      • Furnaces: furnaces are the big machines that are usually kept in back corners or in tiny rooms in basements. Basically, these are in the places where no one ever wants to go because it reminds people of horror movies. But have no fear! While you may come across a couple spiders here or there, the furnace room shouldn’t be intimidating if you know why it’s there. Furnaces are designed to heat air then distribute it to different parts of the home via ductwork or piping. 

      • Boilers: unlike furnaces, boilers use hot water to heat your home. The hot water is distributed through your home using small hot water pipes, pumps, cast iron radiators, or radiant flooring systems. And instead of using hot water to heat the home, steam boilers use (take a wild guess!) steam to achieve their goals. Boilers can be run on oil, gas, electricity, or, for the more environmentally-conscious, wood pellets.   

  • Coils:

    • Coils are used in air conditioners and heat pumps to help them complete the heating or air conditioning process.

      • With air conditioning and cooling, the evaporator coil absorbs heat from your home and the condenser coil pushes it outside. For air conditioning, air from the blower moves over the evaporator coil, and the refrigerant absorbs heat from home’s hot air. When used for heating, the process is reversed and the evaporator coil takes heat from refrigerant and the condenser coil pushes it into the house.

  • Condensing Unit:

    • Condensing units are usually found outside of home and filled with refrigerant gas. The gas is compressed into liquid, which is then pumped through the evaporator coil to be transformed into gas again.

  • Refrigerant lines:

    • Refrigerant lines are lines that carry refrigerant (bet you didn’t see that coming) to a condensing unit in form of gas. Gas is transformed to liquid form then transferred to evaporator coil, to be pushed out into your home.

  • Vents:   

    • Vents are the things that blow out air, usually found on the floor or on the ceiling. They allow different heated and cooled air from the duct system into various parts of your home.


Considering all the different parts that exist in a homeowners’ heating and cooling system, it makes sense that there would be a variety of HVAC systems to choose from! Each type of HVAC system has pros and cons and is better for different homeowners than others.

Different Types of HVAC Systems

  • Heating and air conditioning split system:

    • This is the usual HVAC system, with parts of the HVAC system located both inside and outside of the home. The heating and air conditioning split system includes an air conditioner designed to cool refrigerant outside of the home, and a fan or coil inside the house to make it ready to be pushed through the ducts. Ductwork carries air throughout rooms of home, making sure your temperature is perfect always.

  • Zoned systems:

    • Zoned systems allow you to cool or heat different areas of your home by controlling valves or dampers within ductwork. Dampers block airflow to certain rooms, making some rooms in your home warmer or cooler than others when you decide.

  •  Hybrid system:

    •   Hybrid systems use either gas or electric to heat your home, based on whichever is the most economical. Using electric heat pumps and gas furnaces, your heating costs are protected from huge increases due to the hybrid system's technology: using either gas or electric, it makes sure you're getting the best rate for you.   

  •  Duct-free split system:

    • These are designed to function without (you guessed it!) ductwork. A heat pump, air conditioner, small fan coil, wires, and tubing connect the outdoor unit to a fan coil, which pushes the air through the home.

  • Geothermal system:

    • For up and coming HVAC options, consider geothermal! Geothermal heating and cooling use the Earth's surface, or pond or well water, to heat your home in the winter and cool it off in the summer. Denver, and Colorado in general, has great access to geothermal energy!

  •  Humidity control:

    • We’ve all been there, especially in Denver (keyword): the dry air can make for some difficulty breathing, to say the least. Humidifiers (and dehumidifiers if you need ‘em) can be added to an HVAC system depending on your needs. You can control humidity levels when HVAC is running.


There you have it! You’re now familiar with the different parts of your HVAC system, what those letters stand for, the different types of HVAC system and, most importantly, how HVAC works! With your newfound knowledge, you are ready to go back to your air conditioner and turn it on with confidence.


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