Glossary of Terms

At Durastar, we aim to help our customers better understand which heating and cooling equipment will help them achieve maximum comfort year-round. One way we accomplish this is by breaking down common HVAC acronyms and terms. Be sure to check out our other resources like How To Talk To Your Contractor and Things To Consider When Replacing Your HVAC System.

HVAC acronyms and terms - technical glossary


Annual Fuel Utilization Efficiency (AFUE), is a standardized measure of efficiency for how furnaces and boilers convert energy to useable heat.

Air Conditioner

An air conditioner, or AC unit, cools your home by removing heat and humidity. This is accomplished using an evaporator coil, which collects the warm air, and a condenser coil which releases the collected air outside.

Air Handler

An air handler, also known as a fan coil, is generally paired with a heat pump. Together they create a heating and cooling system. Air handlers are the indoor component and they move air over a coil which then heats or cools the air. After that, it distributes the air throughout your home via ductwork.

Amp Draw

Amp draw measures the amount of effort or energy it takes to run a piece of equipment.


BTU, also known as the British Thermal Unit, is a measure of both heat loss and gain. Specifically, it measures the heat given off when fuel is combusted; or when cooling, it measures the heat that is extracted from a space. Talk with your contractor to determine how many BTUs are ideal for your home. Too many or too few BTUs will cause excess energy costs, unnecessary wear and tear, inconsistent temperatures throughout your space, and other adverse results.


In terms of HVAC systems, capacity refers to the maximum output of a unit. In other words, a system’s ability to heat or cool a specific amount of space. The larger the unit is, generally, the greater the output. For cooling, capacity is measured in tons; and for heating it is measured in BTUs.


CFM stands for cubic feet per minute. In regards to HVAC systems, CFM is measuring airflow. Specifically, how many cubic feet of air passes over a single point in the span of one minute. When a system has a high CFM rating, it means a greater amount of air is being forced through it.


Coils are a key component of air conditioning and heat pump systems. In fact, evaporator coils and condenser coils are responsible for continuously circulating refrigerant between indoor and outdoor components.

Decibel Rating

Decibels are a measurement of sound. The lower the decibel rating (dB) the quieter your equipment will operate.


ECM is short for electronically commutated motor and uses less wattage than a standard motor. This type of motor is also referred to as a variable-speed motor. It enhances the efficiency of your HVAC system by lowering the amount of energy required to maintain consistent airflow in your home. Due to the motor’s microprocessor, it is able to regulate the airflow based on the demands of the environment. As a result, it will operate at the lowest power output in order to maintain the designated temperature.


EER2 is an energy efficiency rating specific to air conditioners and cooling systems. The higher the EER2 rating, the more energy-efficient your air conditioner operates.


HVAC equipment with the ENERGY STAR symbol has met strict energy efficiency criteria set by the US Environmental Protection Agency. The ENERGY STAR rating was established to help reduce greenhouse gas emissions caused by inefficient energy consumption. These products can often help reduce your monthly utility bills.


A furnace heats air which is then distributed throughout your home via ductwork.

Heat Pump

A heat pump is an outdoor unit that uses electricity to both heat and cool your home. They operate by extracting heat from a nearby space and then transferring it to another space. Because the unit transfers heat, rather than generating it, it can be more energy efficient when compared to other equipment such as air conditioners or furnaces. However, discuss all options with your contractor because there are many factors to consider when deliberating energy efficiency, such as your climate and home’s specifications. These units are generally paired with an air handler.


Heating seasonal performance factor, or HSPF2, measures the efficiency of a heat pump. The higher the HSPF2 rating, the greater the likelihood of generating monthly energy savings.

Inflation Reduction Act

The Inflation Reduction Act is a legislative package that incentivizes energy efficiency improvements, such as new or updated heating and cooling systems. To review the 2023 updates, download this helpful PDF and learn about your potential tax incentives.


A mini-split is a ductless and discrete heating and cooling system. Each system has an outdoor compressor that is connected to one or more indoor units. Mini-splits are an ideal solution for individualized, zone-specific temperature control. Build with Ferguson offers a vast selection of mini-split units available for direct purchase, however, we recommend working with an HVAC professional to both determine the best combination of equipment and to ensure proper installation. Please note that warranties may be voided if the product is not installed by a licensed HVAC contractor.


SEER2 stands for Seasonal Energy Efficiency Ratio 2. It is an efficiency measurement used to compare air conditioners and heat pumps. The higher the SEER2 rating, the more efficient the equipment operates.


In HVAC, stages represent the available operating capacities. For example, a single-stage system is either on, using full power, or off. Whereas a two-stage system can operate at two capacities; generally using either 60-65% power or 100% power. Likewise, three-stage systems often have LOW, MEDIUM, or HIGH settings. Units with multiple stages are likely to generate energy savings and can better adjust to varying outdoor conditions to maintain consistent performance and evenly distributed indoor temperatures.


Ton or tonnage is a unit of measurement that measures how much heat an AC unit removes in one hour. When selecting a new air conditioner, it is important to determine the optimal tonnage for consistent, reliable temperature control. In order to do so, you will need to know the square footage of your space. Discuss these details and more with your contractor to ensure you invest in the best HVAC system for year-round comfort.

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