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Mr. Duct is Chicagoland’s Most Trusted HVAC Professional
Mr. Duct is Chicagoland’s Most Trusted HVAC Professional

Understanding HVAC Terminology

Below is a comprehensive guide detailing some commonly used HVAC terms in the heating, ventilation and air conditioning industry. We hope it will help our customers to better understand the technical terms of the HVAC industry, as well as provide a better understanding of heating and cooling systems while performing research on new units or assessing a solution to a furnace, air conditioner or ventilation problem you might have!

A — C

AFUE
Annual Fuel Utilization Efficiency. Indicated as a percentage, your furnace's AFUE tells you how much energy is being converted to heat. For example, an AFUE of 90 means that 90% of the fuel is being used to warm your home, while the other 10% escapes as exhaust with the combustion gases.

Advanced Reciprocating Compressor
Type of compressor that uses a more efficient process for compressing refrigerant for better cooling efficiency.

Air Handler
The portion of your air conditioner or heating system that forces air through your home's ductwork.

BTU
British Thermal Unit. Used for both heating and cooling, BTU is a measure of the heat given off when fuel is combusted. Or for cooling, it's a measure of heat extracted from your home. (One BTU is approximately equal to the heat given off by a wooden kitchen match.)

BTUH
A British Thermal Unit (BTU) is the unit of heat required to raise 1 pound of water by 1 degree Fahrenheit. BTUH is British Thermal Units per Hour.

CFM
Stands for Cubic Feet per Minute. A measurement of airflow that indicates how many cubic feet of air pass by a stationary point in one minute. The higher the number, the more air is being forced through the system.

Capacity
The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTUs. For cooling, it is usually given in tons.

Carbon Monoxide (CO2)
A colorless, odorless, highly poisonous gas produced when carbon-based fuels, such as natural gas, burns without sufficient air nearby.

Compressor
Part of the heat pump or air conditioner unit that controls the pressure applied to the refrigerant, necessary for taking in heat to warm your home or getting rid of heat to keep your home cool.

Condenser Coil
Part of the outdoor portion of a split-system air conditioner or heat pump. By converting refrigerant that is in a gas form back to a liquid, the coil sends heat carried by the refrigerant to the outside. Also referred to as an Outdoor Coil.

Continuous Fan Switch
A feature on an oil furnace allowing the furnace's fan to blow continuously to improve system efficiency and maintain even temperatures.

Control System
Thermostat, Thermidistat™ or Evolution™ Control device used by homeowner to set temperature and other settings.

D — G

DB
Decibels (dB) are a unit measuring the intensity of noise.

Damper
A type of "valve" used in duct work that opens or closes to control airflow. Used in zoning to control the amount of warm or cool air entering certain areas of your home.

Downflow
A type of furnace that takes cool air from the and blows warm air to the bottom-common where your furnace must be located in a second-floor closet or utility area.

Ductwork
Hollow pipes used to transfer air from the Air Handler to the air vents throughout your home. Ductwork is one of the most important components of a home heating and cooling system.

EER
Energy Efficiency Ratings (EER) measure the efficiency with which a product uses energy to function. It is calculated by dividing a product's BTU output by its wattage.

Electronic Air Cleaner (EAC)
An electronic device that filters out large particles and contaminants in indoor air. It then electronically pulls out tiny particles that have been magnetized, such as viruses and bacteria, drawing them to a collector plate.

Energy Saver Switch
An energy-saver switch causes the air conditioner's fan and compressor to cycle on and off together, reducing energy use.

ENERGY STAR™
ENERGY STAR™ is a government-backed program helping businesses and individuals protect the environment through superior energy efficiency. Products with the ENERGY STAR™ rating will be efficient and save cost on energy bills.

Evaporator Coil
Part of a split-system air conditioner or heat pump located indoors. The evaporator coil cools and dehumidifies the air by converting liquid refrigerant into a gas, which absorbs the heat from the air. The warmed refrigerant is then carried through a tube to the outdoor unit (condenser coil). Also referred to as an indoor coil.

Fan Coil
An indoor component of a heat pump system, used in place of a furnace, to provide additional heating on cold days when the heat pump does not provide adequate heating.

Freon™
The trade name Freon™ is a registered trademark belonging to E.I. du Pont de Nemours & Company (DuPont). Production of Freon™ will cease in 2015 per the Montreal Protocol.

H — L

HSPF
The Heating Seasonal Performance Factor is a measure of the heating efficiency of a heat pump. The higher the HSPF number, the more efficiently the heat pump heats your home.

HVAC
Term used for Heating, Ventilation, and Air Conditioning

Heat Exchanger
The part of a furnace that transfers heat to nearby air. That air is then distributed through the ductwork throughout your home.

Heat Pump
A heating and air conditioning unit that heats or cools by moving heat.

Horizontal Flow
A type of furnace, installed on its "side", that draws in air from one side, heats it and sends the warm air out the other side. Most often used for installations in attics or crawl spaces.

Humidifier
A piece of equipment that adds water vapor to heated air as it moves out of the furnace. This adds necessary moisture to protect your furnishings and reduce static electricity.

Humidistat
A control used to manually maintain humidity at a fixed point.

Hybrid Heat
Hybrid Heat systems deliver exceptional performance by using a heating source that provides the most energy-efficient comfort during moderate heating conditions.

IAQ
Indoor Air Quality (IAQ) refers to the cleanliness and health of the air in a home.

Indoor Coil
see Evaporator Coil

Load Estimate
A series of studies performed to determine the heating or cooling requirements of your home. An energy load analysis uses information such as the square footage of your home, window or door areas, insulation quality and local climate to determine the heating and cooling capacity needed by your furnace, heat pump or air conditioner. When referring to heating, this is often known as a Heat Loss Analysis, since a home's heating requirements are determined by the amount of heat lost through the roof, entry ways and walls.

Low Boy
Low Boy is a type of furnace configuration in which the furnace is lower in height and occupies more floor space.

M — P

MERV
The Minimum Efficiency Reporting Value is the standard comparison of the efficiency of an air filter. The MERV scale ranges from 1 (least efficient) to 16 (most efficient), and measures a filter's ability remove particles from 3 to 10 microns in size.

Matched System
A heating and cooling system comprised of products that have been certified to perform at promised comfort and efficiency levels when used together, and used according to design and engineering specifications.

Multipoise
A multi-direction configuration that allows for both upflow and downflow installations.

Operating Cost
The day-to-day cost of running your home comfort equipment, based on energy use.

Outdoor Coil
see Condenser Coil

Payback Analysis
Overall measure of the efficiency and value of your home comfort system. By combining your purchase price and ongoing operating costs, a payback analysis determines the number of years required before monthly energy savings offset the purchase price.

Q — S

R-22 Refrigerant
R-22 is a single component HCFC refrigerant with low ozone depletion potential. It has long been used in a variety of air-conditioning and refrigeration applications in a variety of markets. Production of R-22 will cease in 2015 per the Montreal Protocol. Also commonly known as Freon.

Reciprocating Compressor
A type of compressor used in air conditioners that compresses refrigerant by using a type of "piston" action.

Reclaiming
Involves returning used refrigerant to the manufacturer for disposal or reuse.

Recycling
Removing, cleaning and reusing refrigerant.

Refrigerant Lines
Two copper lines that connect the Condenser (Outdoor) Coil to the Evaporator (Indoor) Coil.

SEER
The Seasonal Energy Efficiency Ratio is a measure of the cooling efficiency of your air conditioner or heat pump. The higher the SEER number, the more efficient the system is at converting electricity into cooling power.

Scroll Compressor
A specially designed compressor that works in a circular motion instead of an up-and and-down piston action.

Setback Thermostat
A state-of-the-art electronic thermostat with a built-in memory that can be programmed for different temperature settings at different times of the day.

Single Package
One outdoor unit that contains both a heating and a cooling system.

Split System
Refers to an air conditioner or heat pump that has components in two locations. Usually, one part of the system is located inside (evaporator coil) and the other is located outside your home (condenser coil).

T — Z

Thermidistat
The Thermidistat Control monitors temperatures both inside and outside, as well as indoor humidity and adjusts system operation to maintain the temperature and humidity levels set by the homeowner.

Thermostat
Unit that monitors and controls your HVAC system products.

Ton
A unit of measure for cooling capacity. One ton = 12,000 BTUs per hour.

Total Home Comfort System
The ultimate solution to providing you with consistent, customized home comfort, despite the ever-changing weather.

UL
UL is an objective, non-profit organization that tests and rates electrical products for public safety.

Upflow
A type of furnace that draws cool air from the bottom and blows the warmed air out the into the duct work. This type of furnace is usually installed in a basement or an out-of-the-way closet.

Ventilator
A ventilator captures heating or cooling energy from stale indoor air and transfers it to fresh incoming air.

Zoning
A way to increase your home comfort and energy efficiency by controlling when and where heating and cooling occurs in a home. Programmable thermostats are used to control operating times of the equipment. Dampers are used to direct air flow to certain parts or "zones" of the home.

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