Terms to Know

Your definition of comfort may be different than your neighbor’s. Knowing the definitions of some of the most commonly used terminology when referring to heating and cooling will tell you what you need to know when discussing your HVAC system with a Twin Oaks Comfort Specialist.

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AFUE– Annual Fuel Utilization Efficiency. The formula for conversion of a gas furnace from fuel to energy. The higher the rating, the more efficient the unit.

Air Handler– The indoor component that moves the heated or cooled air throughout the duct work in your home. An Air Handler is usually a fan coil or a furnace.



BTU– British Thermal Unit. The amount of energy needed to change the temperature of one pound of water, by one degree Fahrenheit. In your home, this represents the measure of heat given off when fuel is burned for heating or the measure of heat extracted from your home for cooling. We use this measurement to determine the exact capacity of heating or cooling your home requires.



CAE– Combined Annual Efficiency. The measurement of heat produced for every dollar of fuel consumed for both water and home heating.

Capacity– The output or producing ability of a piece of heating or cooling equipment. Heating and cooling load capacities are measured in BTU’s per hour.

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Carbon Monoxide-CO– A poisonous, odorless, flammable gas produced when carbon burns with insufficient oxygen. Poor combustion is just one cause of CO. This gas is deadly.

CFM– Cubic Feet per Minute. A standard measure of air flow volume. A conventional system requires 400 CFM per ton [12,000 BTUH] of air conditioning.

Compressor– It is the heart of the outdoor unit and is the central point of a heat pump or air conditioning system. The compressor pumps, or compresses, the refrigerant gas into the condenser, coil, then liquid metered into the evaporator coil to be re-circulated. This cycle occurs to meet the cooling, or in the case of a heat pump, the heating also, requirements of the structure.

Condensing Unit– The outdoor unit, component of an air conditioning system.

Condenser Coil– The condenser coil is always the outdoor coil on a central air conditioning system, but changes on a heat pump system. On heat pump cooling, the condenser coil is outside, just like an air conditioning system, however, in the heating mode the inside coil becomes the condenser. The sole purpose of the condenser coil is to change the state of the refrigerant from a gas to a liquid.

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DB– Decibel Level Sound level or noise level.

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Damper– A moveable plate[s] that opens or closes to control air volume. Often times, dampers are used to balance airflow in a duct system. Dampers can also be used in zoning systems to regulate airflow to different rooms automatically.

DOE– Department of Energy is a federal agency responsible for establishing industry efficiency standards and monitoring the consumption of energy sources.

Ductwork– Pipes, cavities or rectangular channels that carry forced air throughout a home, structure, office, store, etc. The performance of your HVAC system is dependent upon these ducts to carry treated air to where it is needed.



EAC– Electronic Air Cleaner. Equipment that filters air down to microscopic size. Some pollens, bacteria and viruses can be filtered and destroyed with some systems. Indoor air quality.

Energy Star– A label used to identify those HVAC equipments that meet, or exceed, the EPA guidelines for energy efficiency.

EPA– Environmental Protection Agency. The EPA develops and enforces federal environmental regulations. In addition the EPA is responsible to oversee the Energy Star Program.



Gas furnace heat exchanger transfers heat to surrounding home air from the blower. It is then circulated throughout the home via the ductwork while the combustion gases are expelled to the outside.



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Heat Pump– An HVAC unit that cools or heats by transferring or moving heat from one space to another. In the winter, a heat pump draws heat from the outdoor air and circulates it through your home or office air duct system. During the summer, the heat pump reverses the process and removes heat from your home or office and releases it to the outdoors. Heat pumps are an excellent value for our latitude of 39 degrees.

HSPF– Heating Seasonal Proficiency Factor is a rating to measure the heat efficiency of a heat pump. The higher the number the more efficient the unit.

Humidifier– An indoor air quality product that deposits moisture to heated air as it passes from the furnace into the ductwork to distribute throughout the home. Warm air with a relative humidity of 50% feels warmer than heated air at 20% at the same temperature and is healthier.

Humidistat– An automatic control device used to maintain the humidity at an adjustable value of relative humidity.

HVAC – Heating Ventilating Air Conditioning



Indoor Coil– The indoor coil will get cold as the blower from your furnace or air handler passes warm air across it during summer for air conditioning. For a heat pump system this coil operates the same as AC in the summer, but exchanges warm air in the winter as the coil can be an evaporator in the summer and a condenser in the winter.

ISO 9000– A unit of International Standards Organization for quality management and assurance.

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MERV RATING– Minimum Efficiency Reporting Value. This rating is used to rate an air filter, describing the size of the holes in the filter that allows air to pass through. The higher the MERV rating, the smaller the holes are in the filter and the higher the efficiency.

Micron– A unit of measure equal to one millionth of a meter, or one thousandth of a millimeter.




Odors / Chemicals– Air contaminants in the form of gas.



Package Unit– A heating and/or cooling unit that comes together in one self contained package.

Particles– Any substances measuring less than 100 microns in diameter. According to the EPA, small particles that are smaller than 2.5 microns cause the greatest health concern.

Programmable Thermostat– A thermostat that has the ability to record different temperatures and time settings for controlling a heating and/or cooling system.

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Refrigerant– What many consumers refer to as Freon, Puron and other trade names. The fluid and/or gas that evaporates and condenses throughout a system; absorbing heat in the evaporator coil and releasing that heat in the condenser. R-22 Refrigerant is used in 95% of all residential air conditioning equipment. R-22 is regulated by international controls under the Montreal Protocol and in the United States by the EPA. This refrigerant is being phased out and will not be manufactured after 2020. Refrigerant R-410A [Puron] is rapidly becoming a mainstream alternative to R-22 but cannot be used in the same equipment.

Refrigerant Lines – Lineset- Two [2] copper lines that connect the outdoor unit to the indoor unit.



Scroll Compressor– A new designed compressor that operates in a circular motion as opposed to the up and down piston action.

SEER– The Seasonal Energy Efficiency Rating referring to the energy efficiency of an air conditioner or a heat pump. The higher the SEER, the more superior the energy performance, resulting in utility savings, more efficient and a smaller carbon footprint.

Single Package Unit– A heating and/or cooling system contained in one outdoor unit or package.

Split System– A combination air conditioner or heat pump with both indoor and outdoor components. Generally more efficient than package units.



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Thermidistat– Monitors both humidity and temperature and controls heating, cooling and humidity to preferred levels.

Thermostat– A control device consisting of sensors and relays that monitor and activate the functions of cooling, heating and air devices in order to regulate temperature for a specific space.

Ton– Unit of measurement for sizing cooling capacity. One ton is equivalent to 12,000 BTuh.

Two-Stage Operation– Provides two [2] BTU capacity levels saving money and creating a more comfortable air delivery.



Upflow– A type of furnace or air handler that draws cool air from the equipment bottom and discharges warm or conditioned air from the equipment top into, or out of air ducts.



Variable Speed Drive– Automatically adjusts the volume control of airflow for better comfort, less noise and more efficiency.

Ventilator– A system that exchanges stale, re-circulated indoor air with fresh, filtered outside air.



Zoning– A method of dividing a space, home or office, into independently controlled comfort areas for enhanced comfort and efficiency.

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