In alternating current, the current goes from zero potential or voltage to a maximum in one direction, back to zero, and then to a maximum potential or voltage in the other direction. The number of complete cycles per second determines the current frequen ...

A type of water heater that has no storage tank thus eliminating storage tank standby losses. Cold water travels through a pipe into the unit, and either a gas burner or an electric element heats the water only when needed.

A heating system that uses only outside air for combustion and vents combustion gases directly to the outdoors. These systems are less likely to backdraft and to negatively affect indoor air quality.

Solar collector thermal performance ratings based on collector efficiencies, usually expressed in Btu per hour for solar collectors under standard test or operating conditions for solar radiation intensity, inlet working fluid temperatures, and ambient te ...

The unit price of a good or service estimated from some base year in order to provide a consistent means of comparison.

The minimum temperature at which combustion of a solid or fluid can occur.

A salt, sodium sulfate decahydrate, that melts at 90 degrees Fahrenheit; a component of eutetic salts that can be used for storing heat.

The price paid for goods or services at the time of a transaction; a price that has not been adjusted to account for inflation.

A seal used to prevent the leakage of fluids, and also maintain the pressure in an enclosure.

The process of cooling by which a heat absorbing media absorbs heat from one source and radiates the heat away.

A hydrocarbon gas obtained from underground sources, often in association with petroleum and coal deposits. It generally contains a high percentage of methane, varying amounts of ethane, and inert gases; used as a heating fuel.

A coil of tungsten wire suspended in a vacuum or inert gas-filled bulb. When heated by electricity the tungsten "filament" glows.

The ratio of fuel energy input as heat per unit of net work output; a measure of a power plant thermal efficiency, generally expressed as Btu per net kilowatt-hour.

The rate of heat flow required to maintain a specific indoor temperature; usually measured in Btu per hour.

A valve used to mix heated water with cold in a heating system to provide a desired water temperature for end use.

The heat that flows from the building interior, through the building envelope to the outside environment.

Individual rooms or zones in a building where temperature is controlled separately from other rooms or zones.

The ratio of the percentage change in the quantity of a good or service demanded to the percentage change in the price.

A house built using passive solar design techniques.

A building energy auditing technique for locating areas of low insulation in a building envelope by means of a thermographic scanner.