Annual Fuel Utilization Efficiency (AFUE): A measure of how well a furnace converts energy into heat, expressed as a percentage of the annual output of heat to the annual energy input. The higher the percentage, the more efficient the furnace.

Air-to-Air Heat Exchanger: A term referring to a ventilation system which recovers heat from warm exhaust air and transfers this heat to the cold incoming air. Correct installation and balancing are critical to proper operation.

Blower Door Test: A test to determine the air leakage in a home. It uses a variable-speed fan to pressurize or depressurize a house. The pressure difference between the inside and outside air at various fan-induced pressures indicates the amount of air leakage.

British Thermal Unit (Btu): The amount of heat required to raise the temperature of one pound of water from 62º to 63º Fahrenheit or roughly the amount of heat given off by a match.

Circuit Breaker: A device designed to open a circuit to prevent damage from higher voltage.

Coefficient of Performance(COP): The ratio of total useful work output by a machine to the net energy input.

DOE: Department of Energy

Electric cooperative: Consumer-owned provider of electricity, owned and operated on a not-for-profit basis.

Energy Efficiency Ratio (EER): Standard air-conditioning performance rating, defined by the U.S. D.O.E. Air-Conditioning Test Procedure. The EER is a measure of the efficiency of a heating or cooling appliance that is equal to the unit's output in Btus per hour divided by its consumption of energy, measured in watts, under specific test conditions.

Heat Pump: A device that extracts available heat from one area and transfers it to another to either heat or cool an interior space. During the winter, a heat pump extracts heat from the air outside and transfers it to the inside of the house and during the summer, it extracts heat from the air inside the house and transfers it outside.

Heating Seasonal Performance Factor (HSPF): The total heating output of a heat pump during its normal annual usage period for heating divided by the total electric power input in watt-hours during the same period. The higher the HSPF rating, the more efficient a heat pump is at heating.

HVAC Systems: Heating, ventilation, and air conditioning systems. 

Infiltration: The undesirable flow of air into a building through cracks and around doors, windows and other openings in the building envelope. Infiltration is generally accompanied by exfiltration, the flow of air out of the building.

Kilowatt (kW): 1 kilowatt (kW) = 1,000 watts.

Kilowatt Hour (kWh): The basic unit of electric energy equal to 1 kilowatt or 1,000 watts of power used for one hour. The amount of power the customer uses is measured in kilowatt hours (kWh). A 100-Watt light bulb operated for 10 hours uses 1 kWh.

Load: The amount of electricity being used at one time by a customer, circuit or system. Also, the total demand for service on a utility system at any given time.

Low Emissivity (Low-E) Coatings: Coatings on window glass that reduce the amount of heat windows transmit through radiation. They're designed to help keep heat in in winter and out in summer.

Margins: Profits, or excess revenues, allocated to customer accounts based on the amount each customer pays Jackson EMC for service during the year. With board approval, refunds are made annually, usually in December.

Megawatt: 1 million watts or 1,000 kilowatts.

Phantom load: When appliances continue to draw a small amount of power when switched off.

R-Value: A measure of a substance's insulating value or resistance to heat flow. The higher the R-value, the greater the insulating ability.

Seasonal Energy Efficiency Ratio (SEER): Air-conditioning performance rating describing the seasonal performance of an air conditioner or heat pump for a typical residential load. SEER is equal to the total annual cooling output in Btus divided by total electrical energy input in watt-hours. The higher the SEER, the more efficiently the unit cools.

Solar Heat Gain Coefficient: Measures how well a window blocks solar heat. The lower the number, the less heat the window transmits.

Standby Loss: Standby loss is the heat that escapes from water heater storage tank.

U-Value or U-Factor: A measure of a material's ability to conduct heat. The thermal performance of windows and doors is commonly stated in U-values. U-value is equal to 1/R (R-Value). The lower the U-value, the greater the resistance to heat flow and the better the material's insulating ability.

Vapor Barrier: A material that retards the movement of water vapor through walls, floors and ceilings. Vapor barriers help insulation retain its efficiency and keep moisture from building up in a home.

Watt: An electrical unit of power. This term is commonly used to rate appliances using relatively small amounts of electricity. Wattage is stamped on light bulbs and all appliances.