HVAC Glossary
Providing “Comfort for Life” since 1972
Family-Owned
& Operated Since 1972
Third-Generation
Charleston Company
Trane
Comfort Specialist
- Family-Owned & Operated Since 1972
- Third-Generation Charleston Company
- Trane Comfort Specialist
Heating and Cooling Terms, Plain and Simple
The HVAC industry has its own vocabulary, and it can be hard to follow along when a technician is explaining what is going on with your system. We put this glossary together so you always know what you are hearing and can feel confident asking questions and making decisions about your home’s comfort.
If you come across something that is not on this list or want to talk through what a term means for your specific situation, give us a call. We are always happy to help.
- Air Balance The process of adjusting airflow throughout a home so that each room receives the right amount of conditioned air. A properly balanced system improves comfort, efficiency, and the overall performance of your equipment.
- Air Handler The indoor portion of a split HVAC system that circulates conditioned air through your home’s ductwork. It typically contains the blower motor, evaporator coil, and air filter.
- Air Infiltration The unintended movement of outdoor air into a home through gaps, cracks, and openings in the building envelope. High levels of air infiltration make it harder to maintain consistent indoor temperatures and can significantly increase energy costs, which is a common issue in older Charleston homes.
- AFUE (Annual Fuel Utilization Efficiency) A measurement of how efficiently a furnace or boiler converts fuel into heat over the course of a year. An AFUE rating of 80% means that 80 cents of every dollar spent on fuel is converted into usable heat. Higher AFUE ratings indicate greater efficiency.
- Air Duct The network of channels that carries conditioned air from your HVAC system to the rooms in your home and returns air back to the unit for reconditioning. Well-sealed, properly sized ductwork is essential for efficient system performance.
- Balanced System An HVAC system where the airflow, equipment capacity, and ductwork are all properly matched to the size and layout of the home. A balanced system runs more efficiently, maintains more consistent temperatures, and typically lasts longer than one that is mismatched.
- Blower Motor The motor inside your air handler or furnace that drives the fan responsible for circulating air through your ductwork. Variable speed blower motors adjust their output based on demand, which improves comfort and efficiency compared to single-speed motors.
- Carbon Monoxide (CO) An odorless, colorless gas that can be produced by gas-burning heating equipment when combustion is incomplete. Carbon monoxide is dangerous at elevated levels, which is why proper installation, regular maintenance, and working CO detectors are so important in any home with gas appliances.
- Capacity The amount of heating or cooling output a system can produce, typically measured in BTUs (British Thermal Units) per hour or in tons for cooling equipment. Proper capacity sizing is critical for comfort and efficiency. An oversized or undersized system will struggle to perform well regardless of its efficiency rating.
- Central Air Conditioning A whole-home cooling system that uses a compressor, condenser, and evaporator coil to remove heat and humidity from indoor air and distribute cooled air through ductwork. Central air conditioning is the most common cooling solution for homes in the Charleston area given the demands of our climate.
- Compressor The component of an air conditioning or heat pump system that pressurizes refrigerant and drives the heat exchange process. The compressor is typically located in the outdoor unit and is one of the most important and costly components in the system.
- Condenser The outdoor unit of a split air conditioning or heat pump system. It releases the heat that has been removed from your home’s indoor air to the outside. The condenser coil, compressor, and condenser fan all work together in this unit.
- Condenser Coil The coil located in the outdoor unit where refrigerant releases heat to the outside air. Keeping the condenser coil clean is an important part of routine maintenance, particularly in Charleston where pollen, debris, and coastal air can contribute to buildup.
- Carbon for Air Filtration (CFM) Cubic feet per minute, a measurement of airflow volume. CFM ratings are used to size equipment, ductwork, and ventilation systems appropriately for a given space.
- Damper A movable plate inside ductwork that controls or redirects airflow. Dampers are used in zoning systems to direct conditioned air to specific areas of the home based on demand.
- Dehumidification The process of removing excess moisture from indoor air. In Charleston, where humidity levels are consistently high throughout the warm months, effective dehumidification is just as important as temperature control for maintaining comfortable indoor conditions. Many HVAC systems provide some degree of dehumidification, and dedicated whole-home dehumidifiers are available for homes that need additional moisture control.
- Dual Fuel System An HVAC system that combines a heat pump with a gas furnace backup. The heat pump handles heating during mild weather when it operates most efficiently, and the gas furnace takes over when temperatures drop low enough that the heat pump alone cannot keep up. Dual fuel systems can offer meaningful efficiency advantages in climates like Charleston’s where extreme cold is uncommon but does occur.
- Ductwork The system of channels, usually made from sheet metal, flexible tubing, or fiberboard, that distributes conditioned air from your HVAC equipment throughout your home. Leaky or poorly insulated ductwork is one of the most common causes of inefficiency and uneven comfort in residential HVAC systems.
- EER (Energy Efficiency Ratio) A measurement of an air conditioner’s cooling efficiency at a specific outdoor temperature, typically 95 degrees Fahrenheit. Unlike SEER, which measures efficiency over an entire season, EER reflects performance under peak summer conditions. A higher EER indicates better efficiency when your system is working hardest.
- Evaporator Coil The indoor coil where refrigerant absorbs heat from your home’s air, causing the air to cool before it is distributed through your ductwork. The evaporator coil works in conjunction with the outdoor condenser coil to complete the heat exchange process.
- Expansion Valve A component that regulates the flow of refrigerant into the evaporator coil, controlling the rate at which refrigerant expands and absorbs heat. A malfunctioning expansion valve can affect system performance and efficiency.
- Filter A component that removes dust, pollen, pet dander, and other airborne particles from the air before it passes through your HVAC system. Changing your filter regularly is one of the simplest and most effective ways to protect your equipment and maintain good indoor air quality. In Charleston, where pollen counts can be significant during spring and fall, staying on top of filter changes matters more than many homeowners realize.
- Freon A brand name that is commonly used to refer to refrigerants used in air conditioning systems. Older systems used R-22 refrigerant, often called Freon, which has been phased out due to its environmental impact. Newer systems use more environmentally responsible refrigerants such as R-410A or R-454B.
- Furnace A heating appliance that generates heat by burning fuel, typically natural gas or propane, and distributes that heat through your home via ductwork and an air handler. Furnaces are rated for efficiency using the AFUE measurement.
- Heat Exchanger A component inside a furnace that transfers heat from the combustion process to the air that circulates through your home, while keeping combustion gases separate from your indoor air. A cracked heat exchanger is a serious safety concern that should be addressed immediately by a qualified technician.
- Heat Pump A versatile HVAC system that provides both heating and cooling by moving heat rather than generating it. In cooling mode, a heat pump removes heat from your indoor air and transfers it outside. In heating mode, it reverses the process, extracting heat from outdoor air and bringing it inside. Heat pumps are well suited to Charleston’s climate because our winters are mild enough that the heat pump can operate efficiently throughout most of the heating season.
- HEPA Filter (High Efficiency Particulate Air) A high-performance air filter capable of capturing at least 99.97% of airborne particles 0.3 microns or larger. HEPA filters are used in specialized air purification systems and are particularly beneficial for households with allergy or asthma concerns.
- HSPF (Heating Seasonal Performance Factor) A measurement of a heat pump’s heating efficiency over the course of an entire heating season. A higher HSPF rating indicates greater efficiency. The HSPF2 rating is the updated version of this standard, reflecting more accurate real-world testing conditions.
- Humidity The amount of moisture present in the air. Indoor humidity levels that are too high can make your home feel warmer than it is, encourage mold growth, and cause discomfort. Levels that are too low can cause dry skin, static electricity, and damage to wood furnishings. Managing indoor humidity is an important part of year-round comfort, especially in the Charleston area where outdoor humidity is consistently elevated.
- HVAC An abbreviation for Heating, Ventilation, and Air Conditioning. It refers to the full system of equipment and components responsible for controlling the temperature, humidity, and air quality inside a building.
- Indoor Air Quality (IAQ) A term that refers to the condition of the air inside a home or building, including temperature, humidity, and the presence of pollutants, allergens, and contaminants. Poor indoor air quality can affect health and comfort, and there are a range of products and services available to improve it, including air purifiers, UV lights, humidifiers, dehumidifiers, and ventilation systems.
- JEAC (Joint Efficiency Air Conditioning) A rating standard used in some commercial HVAC applications to assess combined system efficiency. Less commonly referenced in residential settings, but relevant in light commercial work.
- Load Calculation A detailed engineering calculation used to determine the correct size of HVAC equipment for a given home or building. A proper load calculation accounts for the home’s square footage, insulation levels, window placement, local climate data, and other factors. Skipping this step and guessing at equipment size is one of the most common mistakes in HVAC installation, often leading to comfort problems and shortened equipment life.
- LEED (Leadership in Energy and Environmental Design) A widely recognized green building certification program. HVAC systems that meet LEED standards contribute to a building’s overall sustainability and efficiency score.
- Matched System An HVAC system where the indoor and outdoor components are specifically designed and tested to work together. Using matched components ensures that efficiency ratings are accurate and that the system performs as intended.
- Metering Device A component that controls the flow of refrigerant between the high-pressure and low-pressure sides of an HVAC system. Common metering devices include expansion valves and fixed orifices.
- OSHA The Occupational Safety and Health Administration. OSHA sets workplace safety standards that govern how HVAC technicians handle refrigerants, electrical components, and other potentially hazardous materials on the job.
- Outdoor Unit The portion of a split HVAC system located outside the home. In a central air conditioning system, the outdoor unit contains the compressor, condenser coil, and condenser fan.
- Packaged System An all-in-one HVAC unit that contains both the heating and cooling components in a single outdoor cabinet. Packaged systems are a good solution for homes without the space for a traditional split system with separate indoor and outdoor components.
- Plenum A chamber that connects to your HVAC system and serves as a distribution point for conditioned air entering the ductwork or as a collection point for return air. Supply plenums and return plenums are common in residential systems.
- PSI (Pounds per Square Inch) A unit of pressure measurement used when checking and charging refrigerant in HVAC systems. Technicians use PSI readings along with temperature data to assess system performance and refrigerant charge.
- R-22 Refrigerant An older refrigerant used in air conditioning systems that has been phased out due to its ozone-depleting properties. Systems that still use R-22 can no longer be topped off with new refrigerant since production has stopped, and replacement with a current-generation system is generally the most practical path forward.
- R-410A Refrigerant The refrigerant that replaced R-22 in most residential HVAC systems. While R-410A is more environmentally responsible than R-22, it is itself being phased down in favor of newer low-global-warming-potential refrigerants such as R-454B as part of ongoing regulatory changes.
- Refrigerant The chemical compound that circulates through an air conditioning or heat pump system, absorbing heat in one location and releasing it in another to provide cooling or heating. Refrigerant is essential to the operation of any vapor-compression HVAC system.
- Refrigerant Lines The copper tubing that connects the indoor and outdoor components of a split HVAC system and carries refrigerant between them. Refrigerant lines must be properly insulated and sized to support efficient system operation.
- Return Air Air that is pulled back from your living spaces into the HVAC system to be filtered, conditioned, and redistributed. Return air vents are typically larger than supply vents and are located in central areas of the home.
- SEER (Seasonal Energy Efficiency Ratio) A measurement of an air conditioning system’s cooling efficiency over an entire season. Higher SEER ratings indicate greater efficiency and lower operating costs. SEER2 is the updated version of this standard, reflecting more realistic real-world testing conditions.
- SEER2 The updated efficiency rating standard that replaced SEER for new equipment manufactured after January 1, 2023. SEER2 uses a more demanding testing protocol that better reflects actual operating conditions, resulting in ratings that more accurately represent real-world performance.
- Split System The most common type of residential HVAC configuration, consisting of a separate indoor unit and outdoor unit connected by refrigerant lines and electrical wiring. Split systems allow for flexibility in installation and are available in a wide range of efficiency levels.
- Static Pressure The resistance that air encounters as it moves through your ductwork. High static pressure can reduce airflow, strain your equipment, and contribute to noise and comfort problems. Proper duct design and sizing are essential for maintaining appropriate static pressure levels.
- Supplemental Heat Additional heating capacity that activates when a heat pump alone cannot meet the heating demand, typically during colder weather. Supplemental heat is usually provided by electric resistance heating strips built into the air handler or by a gas furnace in a dual fuel system.
- Thermostat The control device that monitors indoor temperature and signals your HVAC system to turn on or off to maintain your desired setting. Smart thermostats offer additional features such as scheduling, remote access, and energy usage reporting that can improve both comfort and efficiency.
- Ton (Cooling Capacity) A unit of measurement for cooling capacity. One ton equals 12,000 BTUs of cooling per hour. Residential systems typically range from 1.5 to 5 tons depending on the size of the home.
- Two-Stage Compressor A compressor that can operate at two capacity levels, typically high and low, rather than simply on or off. Running at lower capacity during moderate conditions allows the system to maintain more consistent temperatures, reduce humidity more effectively, and operate more quietly and efficiently.
- UV Light (Ultraviolet Light) A type of air purification technology installed inside HVAC systems to neutralize bacteria, mold, and other biological contaminants as air passes through. UV lights are a popular indoor air quality upgrade, particularly for households with allergy or respiratory concerns.
- Variable Speed Motor A motor that can adjust its operating speed based on current demand rather than running at a fixed speed. Variable speed blower motors provide more consistent airflow, better humidity control, quieter operation, and improved efficiency compared to single-speed alternatives.
- Ventilation The process of exchanging stale indoor air with fresh outdoor air to maintain air quality and reduce the buildup of pollutants, moisture, and odors. Proper ventilation is an important but often overlooked component of a complete home comfort strategy.
- Zone System An HVAC configuration that divides a home into separate areas, or zones, each with its own thermostat and independently controlled airflow. Zoning allows different parts of the home to be heated or cooled to different temperatures simultaneously, which can improve comfort and reduce energy waste in homes where usage patterns vary from room to room.
Still have questions about your home’s heating or cooling system? Our team is always glad to help. Give Smoak’s Comfort Control a call and one of our NATE-certified technicians will be happy to walk you through whatever you need to know.