Directory of HVAC Terms
Learn about all things related to HVACs
AHRI
AHRI stands for the Air-Conditioning, Heating, and Refrigeration Institute. It is a globally recognized trade association that represents the HVACR (heating, ventilation, air conditioning, and refrigeration) industry. AHRI provides standards, certifications, and educational resources to ensure quality, performance, and safety in HVACR equipment. It certifies the energy efficiency of HVAC equipment and uses independent third-party laboratories to test equipment and verify that manufacturers' claims about their products are accurate.
BTUs - BTU, or British Thermal Unit
In the context of heating, ventilation, and air conditioning (HVAC), BTU is typically used to measure the heating and cooling capacity of systems. As an example, an air conditioner rated at 12,000 BTU can remove 12,000 BTUs of heat from a room per hour.
Compressor
The compressor is often referred to as the "heart" of the HVAC system and is primarily responsible for circulating the refrigerant and maintaining system pressure. It is typically located in the outdoor unit.
Condenser
The condenser responsible for cooling the refrigerant and releasing the heat outside. It is typically located in the outdoor unit.
Evaporator Coil
The evaporator coil's primary function is to absorb heat from the indoor air, allowing the refrigerant to evaporate and cool the air prior to it being circulated throughout the home. It is important in ensuring both the efficiency of the system and the quality of the air as it plays a role in dehumidifying the air.
Gas Furnace
A gas furnace is part of an HVAC system that heats indoor air by burning natural gas or propane.
Heat Pump with Air Handler
Heat Pump: The heat pump operates by transferring heat between the indoors and outdoors. It uses electricity to run the compressor. This process absorbs heat from the outside and releases it indoors for heating, or vice versa for cooling.
Air Handler: The air handler, which is typically paired with the heat pump contains the blower fan and evaporator coil. The blower fan circulates the conditioned air through the ductwork of the home, while the evaporator coil helps transfer heat to or from the air depending on if the system is in heating or cooling mode.
Horizontal vs. Vertical vs. Multiposition HVAC Units
Horizontal units are designed to be installed in a horizontal position so the unit lies flat, with the airflow moving side to side. It is typically ideal for spaces like an attic with limited vertical clearance. Vertical units are designed to be installed in a vertical position so the unit stands upright, with the airflow moving from top to bottom or vice versa. A multiposition unit is flexible and can be installed in multiple orientations: upflow, downflow, horizontal and is adaptable to various spaces and installation needs.
Package System vs. Split System
Package System: An HVAC system that contains all the components for heating and cooling in one unit. It is typically found outside the house on the roof or on a concrete slab next to the home.
Split System: An HVAC system that contains two separate units: an outdoor unit (compressor/condenser) and an indoor unit (evaporator coil and air handler/gas furnace).
Plenum
The plenum is a crucial component of an HVAC system for distributing and returning air, ensuring efficient operation, and maintaining balanced airflow. The supply plenum distributes conditioned air throughout the home, while the return plenum collects air to be reconditioned.
SEER vs. SEER2 vs. EER
EER (Energy Efficiency Ratio) is a measure used to evaluate the efficiency of the air conditioning unit or heat pump. It is calculated as the ratio of total cooling capacity of the unit (in BTUs) divided by the total amount of energy consumed (in watt-hours). A higher EER means a more efficient unit while a lower EER means less efficiency. EER is measured under specific test conditions while Seasonal Energy Efficiency Ratio (SEER) is calculated over the entire cooling season, providing a more comprehensive indication of seasonal performance. SEER2 is an updated DOE standard measurement from SEER effective as of January 1, 2023 that better simulates real world conditions, resulting in SEER2 ratings which are typically lower than SEER ratings.
Single Stage/Two Stage/Variable
Single Stage: A single-stage HVAC system has two settings: on or off. When cooling the home, a single-stage AC will turn on to 100% capacity to reach the desired temperature, and then turn off completely.
Two Stage: A two-stage HVAC system has two levels of operation: low and high. The low stage is used on milder days and runs at a reduced capacity (usually around 60-70% of full capacity) and increases to full capacity when needed. These units are typically more efficient and can have fewer temperature swings than single stage units.
Variable: A variable HVAC system has a wider range of capacities, typically between 25%-100% to maintain the most consistent indoor temperature and humidity. They are typically the most efficient but more expensive due to the more advanced technology and capabilities.
Thermostat
Device that regulates the temperature by controlling the HVAC unit. It senses the ambient temperature and controls the HVAC unit to maintain the desired setpoint temperature.
Tons
Residential HVAC units typically range from 1.5-5 tons (in half ton increments). The tonnage is primarily based on the size of the space the unit is meant to cool. One ton of cooling capacity equals 12,000 BTUs per hour.
Zones
HVAC zoning allows for separate temperature control via separate thermostats in different areas, enhancing comfort and energy efficiency by heating or cooling only occupied zones.
