HVAC Glossary

Your Guide to Understanding Home Comfort Systems

At T.F. O’Brien, we understand that HVAC terminology can seem overwhelming to homeowners and business owners. This extensive glossary is designed to demystify some of the technical language surrounding heating, ventilation, and air conditioning systems. We think this will be a valuable tool to help you make more informed decisions about your home or business’s comfort and quality of air.

Our guide breaks down the essential HVAC concepts you’ll encounter, from core system components to efficiency ratings and maintenance terms. Whether you’re a first-time homeowner or looking to upgrade your existing system, this glossary will help you understand some of the language used by HVAC professionals.

From understanding the basics of how your HVAC system regulates temperature and air quality to deciphering complex efficiency ratings like SEER and HSPF, we’ll walk you through everything you need to know. Learn about critical components, air quality considerations, and key maintenance terms that will help you keep your Long Island home or business comfortable year-round.

Core Concepts:

  • HVAC System: A system that regulates a building’s indoor environment by controlling temperature, humidity, and air quality.
  • BTU (British Thermal Unit): A measure of heat energy, often used to rate heating and cooling equipment. One BTU is the amount of energy required to raise one pound of water by one degree Celsius. A higher BTU rating indicates greater heating or cooling capacity.
  • SEER (Seasonal Energy Efficiency Ratio): A measure of how efficiently an air conditioner uses energy over a cooling season. A higher SEER rating indicates lower energy costs.
  • EER (Energy Efficiency Ratio): A rating that measures air conditioning efficiency at a specific temperature (usually 95°F). While SEER measures seasonal efficiency, EER tells you how efficiently your system will run on the hottest days when you need it most. Higher numbers mean better efficiency.
  • HSPF (Heating Seasonal Performance Factor): A measure of how efficiently a heat pump uses energy to heat a home during a heating season. A higher HSPF rating means lower heating costs.
  • Thermostat: A device that controls the temperature setting for an HVAC system, often programmable or smart.
  • CFM (Cubic Feet per Minute): A measure of how much air flows through your HVAC system. Higher CFM means more airflow, which affects comfort and efficiency.
  • Dehumidification: The process of removing excess moisture from the air to make your home more comfortable and prevent mold growth.
  • Latent Heat: The hidden heat in moisture that affects how humid your home feels. HVAC systems remove latent heat to keep your home cool and dry.
  • AFUE (Annual Fuel Utilization Efficiency): A percentage rating that shows how effectively your furnace converts fuel into heat. For example, an AFUE of 95% means 95% of the fuel becomes heat for your home, while 5% is lost in the exhaust. Modern furnaces range from 80% to 98.5% AFUE.

System Components:

  • Air Conditioner: A system that removes heat and moisture from indoor air, typically using a refrigerant.
  • Air Balance: An HVAC service that involves adding dampers to the plenum of an HVAC system and adjusting them to even out the airflow from the air ducts.
    • Whole Home Air Balance: Air balance for every branch of the air duct, typically done when an HVAC system is replaced.
    • Single Room Air Balance: Air balance for a single branch of air duct, usually done after a replacement.
  • Air Duct: Distribution channels in an HVAC system that allow air to flow from the furnace or air handler to different areas. Air ducts can be round or square. John Moore uses air ducts with an R8 r-value.
  • Air Filter: A device that prevents airborne dust, dirt, and debris from flowing through an HVAC system. One-inch filters, typically found in the grille, should be replaced monthly.
    • Media Filter: An air filter that goes in the duct system and prevents finer airborne particles from flowing through the HVAC system, improving air quality.
  • Air Flow Meter: A meter used to measure the amount of air coming out of an air vent to determine if enough air is flowing to effectively cool a room.
  • Air Handler: A component found in electrical HVAC systems that contains the evaporator coil, heater, and blower.
  • Air Register: A rectangular grill that can be opened and closed to direct airflow. Its placement and size are critical to HVAC system efficiency.
  • Blower: A motorized fan that pushes air through the HVAC system’s ductwork.
    • Blower Components: Blower wheel, blower motor, motor mount, electrical connections, capacitor, fan belt (in some models), bearings, shaft, pulley system, speed control module, vibration dampeners, cooling fins, mounting bracket, wiring harness.
  • Boiler: A device that boils water, with the heat then blown through the HVAC system. Furnaces are more common than boilers in most newer homes.
  • Capacitor: A device that stores an electric charge. In HVAC systems, capacitors charge an electromagnet that keeps the condenser fan spinning.
  • Collar: A component that attaches the air duct to the plenum and holds attachments like dampers in place.
  • Compressor: The component that compresses refrigerant, raising its pressure and temperature. It is the central component of the outdoor unit that compresses refrigerant to the correct pressure and temperature before it passes through the condenser coil.
    • Compressor Components: Compressor housing, electric motor, compression mechanism, crankshaft, pistons, connecting rods, bearings, valves, refrigerant lines, capacitor, thermal overload protector, oil pump, mounting feet, vibration isolators.
  • Condenser (or Outdoor Unit): The outdoor unit that typically houses a heat exchanger, compressor, and a fan to cool the refrigerant inside.
    • Condenser Components: Condenser coil, compressor, condenser fan, fan motor, refrigerant lines, condenser unit housing, mounting pad, electrical connections, capacitor, contactor, refrigerant pressure switches, coil fins, protective grille, vibration dampeners.
  • Condenser Coil: The coil in the outdoor unit that works with the evaporator coil to remove warm air. It cools warm refrigerant after it’s been moved from the evaporator coil.
  • Condensate Drain Line: A drain line attached to the HVAC system that captures and drains condensation from the evaporator coil. They are often constructed from ¾ inch PVC pipes and must be insulated.
  • Damper (or Butterfly Damper): A device with moving parts used to adjust the amount of airflow through an air duct, attached between the collar and the plenum.
  • Drain Pan: A pan that captures condensation coming from the evaporator coil.
  • Duct Design: The mathematical process of resizing ducts according to a home’s heat load calculation, based on Manual D: Duct Design.
  • Ductwork: A network of ducts that distributes conditioned air throughout a building.
    • Ductwork Components: Flexible ducts, rigid metal ducts, duct joints, duct sealant, insulation, duct supports, duct tape, dampers, duct connectors, vent covers, return air grilles, flexible duct connectors, duct hangers, duct insulation tape.
  • ECM (Electronically Commutated Motor): A high-efficiency motor in some HVAC systems that adjusts speed to save energy and improve comfort.
  • Emergency Condensate Drain Line: A secondary branch of the condensate drain line that drains water from the drain pan, typically positioned to be visible under roof soffits.
  • Evaporator Coil: A heat exchanger located within the home (either in the air handler or just outside the furnace) that circulates cold gas and warm refrigerant to cool and absorb warm air.
    • Evaporator Coil Components: Copper tubing, aluminum fins, refrigerant inlet, refrigerant outlet, condensate drain pan, insulation, mounting brackets, coil support frame, anti-corrosion coating, thermal expansion valve, refrigerant metering device, drain line connection, coil cleaning ports, protective coating.
  • Float Switch: A safety device installed in your AC’s drain pan that automatically shuts off the system if water starts to accumulate. This prevents water damage to your home if the condensate drain line becomes clogged. Some areas require these by code.
  • Furnace: A heating system that burns fuel (like natural gas or oil) to heat air, which is then circulated through ductwork. An appliance that contains an air blower and a heating element. In most natural gas HVAC systems, furnaces turn on even when cooling because they contain the air blower.
    • Furnace Components: Burner assembly, heat exchanger, combustion chamber, pilot light or electronic ignition system, gas valve, flame sensor, limit switch, furnace filter, blower motor, control board, inducer motor, flue pipe, thermocouple, pressure switch.
  • Hard Start Kit: A device that helps your air conditioner’s compressor start up more easily, reducing wear and extending system life.
  • Heat Pump: A system that can both heat and cool a home by transferring heat between indoor and outdoor air.
    • Heat Pump Components: Refrigerant lines, reversing valve, compressor, condenser coil, evaporator coil. Expansion valve, outdoor unit fan, indoor air handler, refrigerant, defrost control board, accumulator, crankcase heater, capacitor, refrigerant pressure sensors.
  • Heater: The heating element located within the air handler on an electric HVAC system.
  • Plenum: The air-distribution box attached to the supply outlet of the HVAC equipment that connects to all of a home’s air ducts.
  • Refrigerant: A substance used in air conditioning and heat pump systems to transfer heat. A reusable gas/fluid found in the condenser, used to cool the condenser coil.
    • R-22: An older refrigerant being phased out due to its ozone-depleting properties.
    • R-410a: A newer, more environmentally safe refrigerant.
  • Refrigerant Lines: Pipes that carry refrigerant to and from the evaporator coil.
  • Return Air Grille: The larger grating that holds the HVAC’s air filter.
  • TXV (Thermal Expansion Valve): A small but important part of your AC that controls how much refrigerant flows into the cooling coil, improving efficiency.
  • Vents: Openings in walls or ceilings that allow conditioned air to enter a room.
    • Vents Components: Vent covers, Adjustable louvers, Return air grilles, Supply register, Damper mechanism, Mounting brackets, Decorative frames, Air deflectors, Magnetic vent covers, Filter grilles, Vent screens, Rust-resistant materials, Paintable vent covers, Magnetic vent deflectors.

Air Quality:

  • Air Filter: A device that removes pollutants, allergens, and other particles from the air.
  • ERV (Energy Recovery Ventilator): A system that brings fresh air into your home while keeping your heating or cooling from escaping, improving ventilation without wasting energy.
  • HEPA Filter (High-Efficiency Particulate Air Filter): A super-effective air filter that removes almost all dust, pollen, and pet dander, improving indoor air quality.
  • HRV (Heat Recovery Ventilator): Similar to an ERV, but best for colder climates where humidity control is less of a concern.
  • Indoor Air Quality (IAQ): The quality of the air within a building, affecting health and comfort.
  • MERV Rating (Minimum Efficiency Reporting Value): A rating system for air filters, indicating their ability to capture particles of different sizes. A higher MERV rating means better filtration.
  • Off-Gassing: The release of chemicals from new furniture, carpets, and paints that can affect indoor air quality. HVAC filters and ventilation can help reduce it.
  • UV Light Systems: An add-on air purification device that uses ultraviolet light to kill bacteria, viruses, and mold in your HVAC system. Usually installed near the cooling coil or in the ductwork. While effective against biological contaminants, they don’t filter dust or other particles.
  • Ventilation: The process of introducing fresh air into a building and removing stale air.
  • Whole-House Dehumidifier: Dehumidifiers remove excess moisture during humid weather to improve comfort and prevent mold growth
  • Whole-House Humidifier: Adds moisture during dry winter months to prevent static electricity, dry skin, and wood damage

Maintenance and Troubleshooting:

  • Annual Tune-up: Routine maintenance to ensure optimal performance and energy efficiency.
  • Blower Door Test: A test that checks your home for air leaks, helping improve energy efficiency and comfort.
  • Capacitor Failure: A common issue that prevents your AC from turning on or running properly. It’s an easy fix for a technician.
  • Coil Cleaning: Cleaning the cooling coils in your AC helps it run efficiently and last longer. A professional should do this during routine maintenance.
  • Duct Sealing: Sealing leaks in ductwork to improve energy efficiency and air quality.
  • Filter Bypass: When air sneaks around a clogged or poorly installed filter, reducing efficiency and air quality.
  • Freon Electronic Leak Detector: An electronic device used to detect freon leaks.
  • Refrigerant: A substance used in air conditioning and heat pump systems to transfer heat.
  • Refrigerant Leak: When your AC loses refrigerant, it can’t cool properly. Leaks should be fixed quickly to avoid system damage.
  • Short Cycling: When your AC or furnace turns on and off frequently instead of running in longer, more efficient cycles. This often indicates a problem like an oversized system, dirty filter, or low refrigerant. Short cycling wastes energy, causes excess wear and tear, and fails to properly dehumidify your home.
  • System Calibration: Adjusting the system’s settings to optimize performance.
  • Wet Vac: A large vacuum cleaner used to remove water from an emergency drain pan or condensate drain line.

Additional Terms:

  • Geothermal Heating and Cooling: A system that uses the Earth’s constant temperature to heat and cool a building.
  • Heat Load Calculation: A calculation HVAC technicians use to size equipment for tonnage that takes into account the size of your home, the depth of your attic’s insulation, the state of your air ducts, plants, and any air leaks.
  • HVAC: An acronym that stands for Heating, Ventilation, and Air Conditioning.
  • Relay: A switch that uses low voltage to turn a fan motor off and on.
  • Service Panel/Disconnect: The electrical shut-off box located near your outdoor AC unit. Homeowners should know where this is located in case they need to cut power to the unit during an emergency or for service. It usually looks like a gray or tan metal box mounted on the wall.
  • Smart Thermostat: A thermostat that can be controlled remotely and learns your preferences.
  • Static Pressure: The resistance to airflow in your ductwork. High static pressure can reduce comfort and increase energy bills.
  • Tonnage: Used to rate the size of equipment. One ton is 12,000 BTUs.
  • Two-Stage Systems: HVAC equipment that can operate at two different levels – usually “high” for very hot or cold days, and “low” for mild weather. This provides better efficiency than single-stage systems while being more affordable than variable speed equipment.
  • Variable Speed Systems: Advanced HVAC systems that can run at different speeds instead of just “on” or “off.” These systems run longer at lower speeds, providing better temperature control, improved humidity management, and higher efficiency. They’re quieter and more comfortable than traditional single-speed systems.
  • Zone System: An HVAC system that has electronic dampers that allow air flow in each room or area of the home to be regulated from the thermostat.
  • Zoning: Dividing a building into different climate zones, allowing for more precise temperature control.