How Does a Heating, Ventilating & Air Conditioning System Work?


Central heating, ventilation, and air-conditioning systems (HVAC) are designed to maintain air quality and comfort in the home. The ventilation system initiates air flow so it can be ventilated, heated, and cooled. The air-conditioning, furnace and heat pump control air temperature and help filter the air so fewer pollutants are circulating throughout the home.

Ventilation Systems

  • There are three major types of ventilation systems: exhaust, supply and balanced. Exhaust ventilation uses exhaust fans to pull air out of the home and reduce the air pressure inside so air flows in naturally from the outside. Supply ventilation does the opposite, pumping air into the building so the old, stale air leaks out. A balanced system uses both exhaust and supply fans so old air is pushed out, but fresh air can still come in.

Air Conditioning

  • Most central air-conditioning is composed of two units: a condenser and evaporator. The condenser is the outside unit, and the evaporator is in the inside unit. The condenser unit transforms a refrigerant, such as Freon, into a high pressure gas. As the gas flows through the tubing towards the inside unit, it looses heat and transforms back into a liquid, until it reaches the evaporator which transforms it into a low-pressure, low-temperature gas. As air circulates through the evaporator unit, the gas form of the refrigerant absorbs heat so cool air can be recirculated through the ventilation system. As the refrigerant heats up, it returns to the condenser unit to start the cycle again.


  • The furnace is connected to the ductwork, which usually has a heat exchange or fan to pull the heat generated by the furnace into the ventilation system so it can be circulated throughout the home. HVAC systems may also use a heat pump to supplement the furnace. A heat pump essentially works in reverse from the central air system. It draws heat from the outside air and moves it through the system to the evaporator which pumps the warm air into the ventilation system.


  • There are a number of problems that can occur with an HVAC system. If the duct work is not installed properly, the system can't maintain enough pressure to circulate the air. This will not only cause poor ventilation, but the furnace and air-conditioner will also need to work harder and will cost more money to run. Filters on the air-conditioner and furnace should be changed regularly. When the filter gets clogged with dirt, mold spores and other debris, these pollutants get circulated throughout the home and reduce overall air quality. Another common problem with an HVAC system is coolant leakage, which will cause the system to run inefficiently or not work at all. If you're having problems with your system, you can hire an HVAC contractor to make sure everything is installed correctly and make repairs if necessary.

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