Glossary

Advanced Reciprocating Compressor

A modern iteration of the traditional "piston-type" compressor, designed to enhance energy efficiency, reduce noise, and improve durability in cooling systems. It uses a crankshaft-driven piston to draw in and compress refrigerant gas, but incorporates modern engineering, such as improved materials, variable speed drives (VSD), and better capacity control systems (like VARISTEP) to handle both low and high-demand operations. 

AFUE - Annual Fuel Utilization Efficiency

A percentage rating measuring how efficiently a furnace or boiler converts fuel (gas, oil) into usable heat over a typical heating season. It acts as a, “miles-per-gallon” for heating systems, with higher percentages indicating less wasted energy. A 90% AFUE means 90% of fuel becomes heat, while 10% escapes.

AHRI - Air-Conditioning, Heating, and Refrigeration Institute

An industry organization that sets performance standards and certifies HVAC equipment for rated capacity and efficiency so consumers and professionals can make accurate comparisons. Representing over 300 global manufacturers of HVACR and water heating equipment. It provides a trusted, voluntary certification program that verifies equipment performance—ensuring efficiency, safety, and capacity—through third-party, independent testing. AHRI-certified products account for over 90% of North American residential and commercial HVACR equipment.

AHRI Certificate Number

A unique identifier listed in the AHRI Directory that verifies matched HVAC system performance. This number is often needed for rebates, incentives, and compliance documentation. 

Air Handler

An indoor HVAC component that circulates conditioned air throughout a home or building. Usually paired with a heat pump or air conditioner, it contains a blower fan, evaporator coil, and filter, acting as the system's "lungs" to distribute heated or cooled air through ductwork. 

Blower

A blower is the fan component inside an HVAC system that moves heated or cooled air through the ductwork and into the living or working space. It plays a critical role in air circulation, comfort, and system efficiency.

Boiler

A boiler is a heating appliance that warms water or produces steam, which is then circulated through radiators, baseboards, or radiant flooring to heat a building.

BTU / BTU-H

British Thermal Unit (BTU) is a measurement of heat energy. BTUH (BTUs per hour) indicates how much heat a system can add or remove in one hour and is commonly used to size HVAC equipment.

Building Envelope

The building envelope is the physical barrier separating indoor conditioned space from the outdoors. It includes walls, insulation, windows, doors, roofs, and floors, and directly affects heating and cooling efficiency.

Capacity

Capacity refers to the amount of heating or cooling an HVAC system can provide. Cooling capacity is measured in tons, while heating capacity is measured in BTUs.

Carbon Monoxide

Carbon monoxide is a colorless, odorless, and potentially deadly gas produced by fuelburning appliances when combustion is incomplete. Proper ventilation and safety controls are critical to prevent exposure.

CFM - Cubic Feet per Minute

CFM measures the volume of air an HVAC system moves in one minute. Proper airflow is essential for comfort, efficiency, and system performance.

Compressor

The compressor is the heart of an air conditioner or heat pump. It pressurizes refrigerant and moves it through the system, enabling heat to be absorbed indoors and released outdoors.

Condenser & Condenser Coil

The outdoor component of an AC system that releases heat absorbed from indoors, transforming refrigerant from gas to liquid. The condenser coil is the specific, finned heat exchanger within this unit where the hot refrigerant releases heat to the outside air.

Conditioned Air

Conditioned air is air that has been heated, cooled, humidified, or dehumidified to maintain a comfortable indoor environment.

Dampers

Dampers are adjustable valves installed in ductwork that control or redirect airflow, often used in zoning systems to regulate temperatures in different areas of a building.

Downflow / Upflow

These terms describe furnace airflow direction. Downflow furnaces push air downward into ductwork, while upflow furnaces push air upward.

Ductwork

Ductwork is the system of metal or flexible passages that distribute conditioned air throughout a building.

EER - Energy Efficiency Ratio

A key metric for HVAC systems, measuring cooling output (BTUs) versus electrical input (watts) at peak conditions (around 95°F outside), with higher numbers indicating greater efficiency and lower energy costs, though it's often compared to SEER (Seasonal EER) for overall seasonal performance. 

Evaporator Coil

The evaporator coil is the indoor heatexchange component where refrigerant absorbs heat from indoor air, cooling and dehumidifying it before circulation.

Heat Exchanger

A heat exchanger transfers heat from combustion gases inside a furnace to the air that circulates through the home, without allowing the gases to mix with indoor air.

Heat Pump

A heat pump is an HVAC system that transfers heat rather than generating it, providing both heating and cooling by moving heat between indoor and outdoor air.

HSPF - Heating Seasonal Performance Factor

A rating of a heat pump’s seasonal heating efficiency — higher values equal better performance.

IAQ - Indoor Air Quality

Indoor Air Quality refers to the cleanliness, humidity level, and overall health of the air inside a building, including the presence of pollutants, allergens, and ventilation effectiveness.

Inverter

A technology that controls the speed of the compressor motor to continuously regulate temperature, rather than turning the motor on and off. It functions like a dimmer switch rather than a simple on/off switch, allowing the system to modulate output, reduce energy consumption by up to 30-40%, increase comfort, and operate more quietly.

Load Estimate

A load estimate calculates how much heating or cooling a building requires based on size, insulation, layout, climate, and other factors.

MERV Minimum Efficiency Reporting Value

A MERV rating indicates how effectively an air filter captures particles such as dust, pollen, and allergens. Higher ratings mean better filtration.

Package Unit Updated term — formerly Single Package Product

A package unit is a selfcontained HVAC system with all heating and cooling components housed in a single outdoor cabinet, commonly used in mobile homes, manufactured homes, commercial buildings, and rooftop installations.

R-22 Refrigerant

An ozone-depleting hydrochlorofluorocarbon (HCFC) refrigerant commonly used in older residential/commercial air conditioners and heat pumps, frequently known by the brand name Freon™. Due to its high environmental risk and ozone depletion, it was phased out by the EPA in the U.S. by 2020.

R-410A Refrigerant

A popular, non-ozone-depleting HFC refrigerant blend (50% R-32, 50% R-125) widely used in air conditioning and heat pump systems. It replaced R-22, offering higher efficiency and cooling capacity, but operates at higher pressures, requiring specialized equipment. Due to its high global warming potential (GWP), it is currently being phased down in favor of more environmentally sustainable alternatives

R-32 Refrigerant

A next-generation, single-component HFC refrigerant used in air conditioning and heat pumps to replace high-GWP options like R-410A. It offers higher energy efficiency, lower global warming potential (GWP of 675—one-third of R-410A), and zero ozone depletion.

R-454B Refrigerant

A low-global warming potential (GWP) refrigerant blend of 70% R-1234yf and 30% R-32. It is designed to replace R-410A in new residential and commercial AC/heat pump systems to meet EPA regulations. R-454B features a GWP of 466—78% lower than R-410A.

Reclaiming vs. Recycling

Reclaiming returns used refrigerant to a certified facility for reuse or destruction. Recycling is the onsite cleaning and reuse of refrigerant.

SEER vs SEER2 - Seasonal Energy Efficiency Ratio

SEER (Seasonal Energy Efficiency Ratio) and SEER2 are metrics measuring HVAC cooling efficiency, with SEER2 acting as the updated, more realistic standard required for all units sold after January 1, 2023. SEER2 uses a more stringent, updated M1 testing procedure that simulates real-world conditions (higher static pressure and tighter ductwork, using 0.5 w.g. vs 0.1 w.g.).

Scroll Compressor

A highly efficient, quiet, and reliable compressor type that uses two interleaved, spiral-shaped scrolls—one fixed and one orbiting—to compress refrigerant. Unlike reciprocating pistons, the orbiting motion reduces moving parts, allowing for continuous, smooth compression as refrigerant is moved from the outer edge to the center. 

Split System

An HVAC configuration with indoor air handler and an outdoor condenser or heat pump component working together to heat and cool.

Thermostat

A thermostat is the control device that senses indoor temperature and signals the HVAC system to heat or cool to the desired setting.

Ton

A ton is a measurement of cooling capacity equal to 12,000 BTUs per hour.

Two-Stage Compressor

A type of compressor that operates at two distinct speeds or capacities—typically a low stage (approx. 65-70% capacity) for mild weather and a high stage (100% capacity) for extreme temperatures. This technology improves efficiency, enhances humidity control, runs quieter, and provides more consistent, balanced temperatures compared to single-stage systems. 

Zoning

Zoning is a method of dividing a building into separate areas with independent temperature control to improve comfort and energy efficiency.