Heating and Cooling Systems Basics


When you feel comfortable in your home, the HVAC system has done its job. Either it has added the atmosphere of warmth, or provided fresh cool air. You hardly think of the process your system goes through to give you this comfort. But, it benefits you to know because HVAC systems require maintenance, and a basic knowledge of the system's operation helps to troubleshoot and identify deficiencies early before you get hit with a massive repair bill.

Air Conditioning

Air conditioning is the process of heating and cooling air, controlling its humidity, and filtering out dust and other pollutants.

An air conditioner transfers heat from the inside of a building, where it is not wanted, to the outside. The refrigerant in the system absorbs the excess heat which is then pumped through a closed pipe system to an outside coil. A fan blows outside air over the hot coil, transferring heat from the refrigerant to the outdoor air. When the heat is removed from the indoor air, the indoor area is cooled. An air conditioning system generally consists of four main mechanical components:

  • Compressor
  • Fan Condenser Coil (Hot)
  • Evaporator Coil (Cool)
  • Chemical Refrigerant

Most central air conditioning systems include a "hot" side, outside your home, and a "cool" side, inside your home. The "hot" side consists of a condensing coil, a compressor, and a fan.

The "cool" side is usually located in your furnace. The furnace blows air through an evaporator coil, which cools the air, and routes this cool air throughout your home using a series of air ducts.

The cleaning function of air conditioners is performed by filters, which remove dust and contaminants from the air. When filters become clogged, they restrict the flow of air and cause the system to operate inefficiently. In some systems, the filters are permanent and can be washed periodically to remove accumulated dirt. Most systems have disposable filters which should be replaced every 30-90 days.

Mechanics of A Heat Pump

A heat pump is like a conventional air conditioner, but it also provides heat in the winter.

Depending on the season, a heat pump runs through two cycles: heating and cooling.

In the summer, the heat pump collects heat from the house and expels it outside. In the winter, the heat pump extracts heat from the outside air and circulates it inside the house. The heat pump works best when the outdoor temperature is above freezing. Below that, additional heat often is needed. A heat pump can use 30 to 60% less energy to supply the same heat when compared to an electric furnace with a resistance heating element.

Cooling Cycle

Refrigerant passes through the indoor coil, evaporating from a liquid to a vapor. As the liquid evaporates, it absorbs heat, cooling the air around the coil. An indoor fan pushes this cooled air through ducts inside the house. Meanwhile, the vaporized refrigerant laden with heat passes through a compressor which compresses the vapor, raising its temperature and pressure. The reversing valve directs the flow of hot, high-pressure vapor to the outdoor coil where the heat released during condensation is fanned into the outdoor air, and the cycle begins again.

Heating Cycle

During the heating cycle, the refrigerant flows in reverse. Liquid refrigerant now flows to the outdoor coil picking up the heat as it evaporates into a low-pressure vapor. The vapor travels through the compressor where it is compressed into a hot, high-pressure vapor, then is directed by the reversing valve to the indoor coil. Then the vapor turns into liquid as it passes through the indoor coil, releasing heat that is pushed through the ducts by the indoor fan.

Understanding Your Furnace

A furnace heats your home by pulling cool indoor air into the furnace, heating it, and then redistributing the warmed air back into the rooms through ductwork.

Furnaces are usually fueled by natural gas, oil, or electricity. Each have differences in how they operate.

Natural Gas Furnace

With a natural gas forced air heating system, gas is mixed with air inside a burner and ignited inside the combustion chamber. A blower pulls cool air in from the rooms through air ducts in the furnace. The air is heated by passing over a heat exchanger connected to the combustion chamber. The warm air then flows back into rooms through ductwork. Exhaust gases from the burners are vented outside through a flue through the roof, or with some models, through a side wall vent.

Oil Furnace

An oil fired furnace operates in much the same way, except the oil is atomized, or turned into a fine mist, and burned. Air absorbs the heat in the exchanger, and a blower sends the warm air back into the rooms through ductwork. Emissions from the burners are then vented outside.

Some homes are equipped with gravity furnaces -- typically in basements -- which use central heating, but not with forced air and blowers. Instead, the heat naturally rises and heats the rooms through ducts.

Electric Furnace

An electric forced-air furnace uses a blower unit to blow air over electrically-heated coils. The warm air is then distributed through the home through ducts. These units can be used with heat pumps or central air conditioners.

Have Questions? Feel Free to Give Us a Call?

Knowing what kind of system you have and the basics of how it operates can help you troubleshoot minor problems and possibly save you money by not having to call a professional for simple fixes. If you want to learn more about your system, feel free to give us a call. We would be more than happy to provide any information you require!