AFUE: Abbreviation for "Annual Fuel Utilization Efficiency," it is an energy-efficiency ratio comparing the useful energy produced by an appliance in a year with the amount of energy it consumes. Thus, the higher the AFUE rating, the better the efficiency.

Boiler: A gas, oil, propane, or solid-fuel-burning appliance that produces hot water or steam which is circulated through pipes to heat-radiating devices in a room.

BTU: Abbreviation for "British Thermal Unit," it is a traditional measurement for the amount of heat needed to raise one pound of water 1°F from a starting point of 39.2°F. BTUH stands for British Thermal Unit Per Hour to measure BTU input or output over time. MBH stands for 1,000 BTUH.

Convected Heat: Warmth transmitted to a colder body through physical contact with a substance, such as air.

DOE: Department of Energy. Under the DOE regulations, manufacturers are responsible for testing to determine the efficiency ratings of residential boilers and reporting ratings to the Federal Trade Commission.

GPM: Gallons per minute.

Heat Exchanger: A device inside a boiler that transfers heat from the burning fuel to the boiler water. The hot water in the boiler is then circulated to radiators, indirect water heaters, hydro-air coils, radiant floor tubing, or other heat-distribution devices.

Home Heating Team Contractor: A designation for heating contractors in the U.S. and Canada who are identified as selling, installing, and servicing Burnham equipment. They are independent contractors not employed by Burnham, so as with any home project, Burnham recommends that homeowners obtain references from any firm they hire.

Hydro-air Coil: A coil of tubes placed in a central air conditioning system through which hot water from a boiler is circulated. The air is heated by passing through the coil, which then circulates into the living space.

I=B=R: Symbol for the Institute of Boiler and Radiation Manufacturers. The Institute tests boilers, baseboards, and commercial finned tube radiation and provides authorization for the use of I=B=R Ratings for those products.

Indirect Water Heater: A separate water storage tank that contains a coil supplied with hot water from a boiler. The coil transmits heat to the water in the tank, which is then piped for domestic hot water use.

MBH: Gas inputs are expressed in MBH, which is thousands of Btu/hour.

PSI: Pounds per square Inch.

Radiant Baseboard: A heat distribution device containing hot water inside a cast-iron or copper-finned radiator that runs along a wall's baseboard.

Radiant Flooring: Special polymer tubing that is run underneath the subfloor or fastened down on top of the subfloor or onto a wire grid imbedded in lightweight concrete. Low-temperature water is circulated through the tubing to produce radiant heat.

Radiator: A cast iron heat distribution device containing hot water or steam that can be a free-standing unit or recessed into a wall.

Radiant Heat: Warmth transmitted to a colder body by the direct contact of infrared rays. See "convected heat."

Tankless Coil: A coil of tubes immersed into the boiler's hot water. Fresh water contained safely inside the coil picks up heat from the boiler water. The coil's hot water is then piped for use in the kitchen, bathroom, or elsewhere.

Zoning: A method of regulating temperatures by using a dedicated thermostat and system of valves and hydronic heating devices for each area of a home.