HVAC 101: What Is an HVAC System & How Does a Furnace Work?

HVAC 101: What Is an HVAC System & How Does a Furnace Work?

Before investing in a new HVAC system for your home, it's helpful to understand what these systems do and how they function. HVAC, or heating, ventilation, and air-conditioning systems, can be some of the most expensive appliances in a home, and they're critical for creating a comfortable environment inside of your home. Read on to learn more about what they are, how they work, and how to maintain yours.

What Is an HVAC System?

Put simply, an HVAC system conditions the air in your home by forcing heated or cooled air throughout the home and removing air that's too cold or hot.

Most HVAC systems include the appliances that heat or cool the home, including furnaces, air conditioning units and heat pumps. They also include any ductwork, controls and thermostats. The most complex systems include central heating and AC systems that rely on ductwork to move the air through the home. 

How HVAC Systems Work

HVAC systems work differently, and the functionality depends on how much space they need to heat or cool. They also function differently based on the exterior environment.

Central Air and Heat System

Central air conditioning systems usually have a separate unit that cools the air moving through the home. The unit has a fan, condenser coil and compressor. The central A/C system usually sits outside of the home and connects to an interior air handler, which also has evaporator coils, along with a furnace for heating. Most central A/C units also have blowers to move cooled or heated air through the ducts. 

Electricity powers the A/C unit, which pumps refrigerant through the system. Warm air in the house gets pushed through the evaporator coils, where the refrigerant vapor cools the air. The cool and dehumidified air eventually returns to the home maintaining the temperature on the thermostat. 

During the cooler season, the furnace portion works to heat the home. Usually, the furnace runs on natural gas, which lights a set of burners to warm the air that's blown through the home.

Packaged Heating and Cooling System

Packaged systems contain the heating element and air conditioning unit in one single package. Technicians usually put them on a roof or in a mechanical room. These elements have fans or blowers that move the warm or cool air through the home. They also work with electricity and forced air, as the central A/C units do. 

Energy Use and HVAC Systems

As more homeowners look for ways to reduce their energy costs, understanding how HVAC systems use energy is important. Most HVAC systems use electricity or natural gas to cool and heat homes. The amount of energy used by any heating and cooling system depends on a few factors:

  • The size of your HVAC units based on your home's square footage
  • The energy efficiency of the appliances
  • What energy powers the units
  • How often you use the units
  • Where you live and your local climate
  • How well you maintain your HVAC units

Heating and cooling appliances receive energy ratings that can help technicians and homeowners make wise energy choices. The rating systems include:

  • SEER (Seasonal Energy Efficiency Ratio): This rating measures the energy efficiency of a heat pump or air conditioning unit. The federal government mandates a minimum rating of 14 SEER
  • AFUE (Annual Fuel Utilization Efficiency): This rating measures how much gas or oil furnaces use and waste. The higher the rating, the better the efficiency. The federal government mandates that furnaces made in the USA have a minimum 85% AFUE
  • HSPF (Heating Seasonal Performance Factor): This rating system measures the efficiency of a heat pump. When the rating is high, the pump is efficient and uses less power. The federal government requires heat pumps to have a minimum rating of 5 HSPF.
  • Wattage: When looking at your heating and cooling components, consider the wattage. The systems use kilowatt-hours, and the EPA uses speed to determine the kilowatt-hours measurement. The more wattage your HVAC system uses, the higher your energy bills will be.

Other HVAC System Options and Features

When choosing a new HVAC system, the best choice is one that makes your home comfortable while using the least amount of energy. 

At a minimum, homeowners and technicians should decide whether to install a multi-stage or single-stage system. The single-stage system either turns on the air conditioning or the furnace to take care of the temperature in your home. The system is either on or off, and the blower runs at one rate. With a multi-stage system, the blower has a variable rate so homeowners can still get warm or cool air, but without the blower at full power at all times.

Other types of systems include 

  • Zoned systems, where HVAC systems open and close valves and dampers to send conditioned air where you need it. 
  • Humidifiers and dehumidifiers, where humidity control helps improve home environments. Humidity controls are added to air conditioning and heating units.
  • Radiant heating systems with water-based heat moved through pipes or flexible tubes under the flooring. 
  • All-electric furnaces for homes that use minimal amounts of heat.

Common HVAC Problems and Maintenance Tips

HVAC systems need routine maintenance. Ideally, you should have an HVAC technician visit your home for a checkup once per year. You can save money by having your furnace inspected in the summer and your air conditioning unit inspected in the early spring. Technicians usually inspect the internal components, clean the fans and coils, and run diagnostic tests on the system to be sure they are functioning at their peak.

Most furnace maintenance involves replacing furnace filters on a regular schedule — often seasonally or every three months. New filters help your furnace and A/C unit send clean air efficiently through your home. With routine HVAC maintenance, you can extend the life of your furnace, heat pump or air conditioning unit. 

Wrapping It Up

After installing a new HVAC system in your home, taking care of it will help it last for more than a decade. The latest HVAC systems are energy-efficient, especially when designed with your home's square footage, exterior environment and zone heating and cooling needs in mind. Choosing an energy-efficient system and using a smart thermostat, which you can program and control from the convenience of your smartphone, can help reduce your energy bills and keep your home comfortable.