Office of Environmental and Energy Coordination

Fairfax County, Virginia

CONTACT INFORMATION: Our office is open 8:30AM-5PM M-F

TTY 711

12000 Government Center Pkwy, Suite 533
Fairfax, VA 22035

Kambiz Agazi,

How To Speak HVAC: Terms To Know When Replacing Your System

As summer reaches its peak, some older heating, ventilation, and air conditioning (HVAC) systems may struggle to keep up with the heat and humidity. Whether you are proactively seeking a new system or reactively replacing an old system that has reached the end of its useful life, it is helpful to know some common HVAC jargon as you make decisions. Below are 15 terms commonly used by professionals in the HVAC industry to describe the features of different systems.

Air Handler: An air handler is a component of an HVAC system and is usually placed indoors. The handler contains a blower, filter racks, as well as heating and cooling elements that aid in the distribution of conditioned air throughout a building.

British Thermal Unit (BTU): Put simply, a BTU is the amount of energy required to raise the temperature of one pound of water by one degree Fahrenheit. This metric is used to help quantify the energy input or output of an HVAC system.

Chiller: Generally speaking, a chiller is a device that removes heat from liquid. Once the liquid is cooled, it can be run through pipes to facilitate air conditioning in a building. Typically, air-cooled chillers are found in outdoor units and water-cooled chillers are within indoor units.

Coil: A coil is an essential component of any HVAC system and many split-systems have one indoor coil (evaporator) and one outdoor coil (condenser). These pieces perform the crucial heat transfer that keeps your home warm or cool, depending on the season. Your evaporator cool pulls heat from the air in the warm months and adds heat to the air in the cool months. The condenser coil regulates the temperature of the refrigerant that circulates through the evaporator coil, allowing it to do its work.

Damper: Your HVAC technician may talk about changing how your dampers are positioned to redirect air flow throughout your home. Dampers are like gates that are placed within your duct work and can usually be controlled from your floor, ceiling, or wall vents. As you engage these gates, open or closed, you change the flow of air through the system, directing more air to certain areas and less to others.

EER (Energy Efficiency Ratio): Not to be confused with SEER (addressed further down on this page), the EER measures the ratio of a system’s output cooling energy to its input cooling energy at a single point in time. While the SEER is calculated over a range of outdoor temperatures, the EER is calculated using specific parameters, namely with an assumed outdoor temperature of 95 degrees Fahrenheit, an indoor temperature of 80 degrees and 50% relative humidity.

Furnace: While sometimes used as a general term for a heating unit, a furnace is a specific component of an HVAC system. This component burns fuel to add heat to the air or to an intermediate fluid that then heats the air.

Heat Pump: A specific type of HVAC system, a heat pump is essentially a compressor. Heat pumps absorb heat from cold areas and release it into warmer areas, they move thermal energy counter to the direction of heat flow and can provide either cold or hot air.

HSPF (Heating Seasonal Performance Factor): Like the SEER (below), the HSPF measures heat efficiency over the course of an entire heating season. The HSPF is expressed in BTU/watt-hour. Currently, federal guidelines require all newly installed heat pumps to have a minimum HSPF of at least 8.2.

SEER (Seasonal Energy Efficiency Ratio): HVAC systems are given a SEER rating as defined by the Air Conditioning, Heating, and Refrigeration Institute (AHRI). SEER ratings give the buyer a sense of how efficiently the system will cool and dehumidify the air. The rating is calculated by dividing the system’s cooling output during a typical cooling season (BTU/year) by the total electricity input during the same period of time. Any split-system central HVAC installed in a Virginia residence is required to have at least a SEER 14 rating. Highly efficient residential systems might achieve an 18 or 19 SEER rating.

Single Stage: A single stage HVAC system has two settings – on and off. When it’s on, it blows air at full blast, responding to your thermostat indicating that the temperature inside has deviated from the set point. Single stage systems can be less efficient as they may turn on and off multiple times in a day and use a good deal of energy to do so.

Split System: The most common type of HVAC system, a split system has an outdoor component and an indoor component. Typically the compressor and condenser coil are outside, while the air handler and evaporator coil are inside.

Thermostat: Your thermostat regulates and monitors the temperature of your home and gives you control of the air flow coming from your HVAC system. Your HVAC unit will respond to changes in the temperature of your home as measured by your thermostat.

Two Stage: A two stage HVAC system is capable of running at high or low speeds, depending on the temperature outside.

Variable Speed: A variable speed HVAC systems outpaces both single stage and two stage systems in the efficiency department. Rather than turning on and off as needed, or running at binary high or low settings, variable speed systems run steadily for long cycles at lower speeds. On a hot summer day, a variable speed HVAC system might run constantly, but only at 25% or 30% of its capacity, keeping a nice, low flow of cool air streaming into your home. This is great for comfort and for energy efficiency.

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