Learn HVAC Terms and Definitions

Be in the Know: List of Common HVAC terms

Below is a glossary of HVAC terminology to provide understanding of these frequently used terms in the industry.

Absolute Pressure

In the larger context of pressure measurement, absolute pressure is part of the “zero reference” trinity. This includes Absolute Pressure (AP), Gauge Pressure and Differential Pressure. AP is zero referenced against a perfect vacuum.

Absolute Temperature

Absolute temperature is the temperature of an object on a scale where 0 is defined as absolute zero. Absolute temperature scales are Kelvin and Rankine. Absolute zero is the lowest temperature at which the system is in a state of lowest possible (minimum) energy. No electronic device can remain functional at this temperature.

Absolute Zero Pressure

Absolute zero, temperature at which a thermodynamic system has the lowest energy. It corresponds to −273.15 °C on the Celsius temperature scale and to −459.67 °F on the Fahrenheit temperature scale.

Absorbent

Ability to pull in and retain liquid: able to absorb liquid.

Absorption Refrigerator

An absorption refrigerator is a refrigerator that relies on a heat source (e.g., solar energy, a fossil-fueled flame, waste heat from factories or district heating systems) that provides the energy necessary to complete the cooling process. The principle can also air condition buildings using the waste heat from a gas turbine or water heater. This multipurpose appliance is highly efficient, since the gas turbine then produces electricity, hot water and air-conditioning (called cogeneration/trigeneration).

ACCA

The ACCA (The Indoor Environment & Energy Efficiency Association) is a nonprofit association whose membership exceeds more than 60,000 professionals and 4,000 businesses in the indoor environment and energy services community. ACCA strives to promote professional contracting, energy efficiency, and healthy, comfortable indoor environments.

Accumulator

An accumulator is a storage tank that holds onto liquid refrigerant from the evaporator and prevents it from affecting suction lines before vaporizing

AFUE

Annual Fuel Utilization Efficiency (AFUE) is the quantity of fuel converted to space heat in proportion to the amount of fuel entering the boiler or furnace. It doesn’t include the electricity consumed by the fan and controls.

AHRI

The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) is a trade association representing manufacturers of HVACR and water heating equipment throughout the globe.

BBB

The Better Business Bureau (BBB) helps people discover and recommend businesses, brands and charities they can trust.

BTU

British Thermal Unit (BTU) is a simple measure of thermal (heat) energy. One BTU is the amount of energy necessary to heat one pound of water one degree Fahrenheit, measured at its heaviest point.

CEE

Consortium for Energy Efficiency (CEE) is a U.S. and Canadian organization of gas and electric efficiency program administrators. CEE works together to accelerate the development and availability of energy-efficient systems and services for lasting public benefit.

COP

Coefficient of Performance (COP) is how we measure efficiency for heat pumps in the heating mode that illustrates the ratio of total heating capacity to electrical energy input. For example, if a heat pump has a COP of 3, it should offer three units of energy for every one unit of electricity consumed.

EER

Energy Efficiency Ratio (EER) of any cooling device is the ratio of output cooling energy (in BTU) to input electrical energy (in Wh) at a specific operating point. EER is generally calculated using a 95 °F outside temp and an inside (actually return air) temp of 80 °F and 50% relative humidity.

HSPF

Heating Seasonal Performance Factor (HSPF) is a measure of a heat pump’s energy efficiency over one heating “season.” It illustrates the total heating output of a heat pump (including supplementary electric heat) throughout the normal heating season (in BTUs) as compared to the total electricity rates (in watt hours) during the same period.

HVAC

HVAC is a common acronym that stands for Heating Ventilation and Air Conditioning. This is the most likely used term when referring to whole-house systems that perform both heating and cooling.

Mini-Split

Mini-split systems are ductless room air conditioners or heaters. When only certain rooms need heating and cooling, mini-split heat pumps and air conditioners provide a smart, all-around solution. Robust efficiency in a small package.

NATE

NATE, North American Technician Excellence Inc., is an independent, third-party, nonprofit certification body for HVACR technicians. NATE certification tests impart real-world working knowledge of HVACR systems and technicians can earn installation and/or service certification in one or more specialty areas. NATE certification tests are developed by the NATE technical committee. The NATE technical committee is comprised of industry experts who developed and monitor NATE’s Knowledge Areas of Technician Expertise (KATEs). Each exam is laid out based on these knowledge areas of expertise. The technical committee represents a wide range of perspectives from contractors, educators, manufacturers and utilities. Members also are diversely spread everywhere in the country.

SEER

Seasonal Energy Efficiency Ratio (SEER) is the cooling output across an average cooling season divided by the total electric energy input in the same period. The higher the unit’s SEER rating the more energy efficient it is.

SHGC

Solar Heat Gain Coefficient (SHGC) is a measure of how effectively a window reflects heat caused by sunlight.

U-Factor

U-factor is a measure of how well a window performs at stopping heat flow. Try windows with a lower U-factor (the lower the U-factor, the better).