Text Box: Definitions of Terms Related to HVAC Systems
Air duct—A formed conduit that carries warm or cold air from the furnace or air-conditioner and back again.
Antiflooding Control—A safety control that shuts off fuel and ignition when excessive fuel oil accumulates in the appliance.
High heat—A unit that operates with flue entrance temperature of combustion products above 1,500°F (820ºC).
Medium heat—Same as high-heat, except above 600°F (320ºC).
Low heat—same as high-heat, except below 600°F (320ºC).
High pressure—A boiler furnishing pressure at 15 psi or more.
Low pressure (hot water or steam)—A boiler furnishing steam at a pressure less than 15 psi or hot water not more than 30 psi.
Burner—A device that mixes fuel, air, and ignition in a combustion chamber.
Carbon monoxide (CO) detector—A device used to detect CO (specific gravity of 0.97 vs. 1.00 for oxygen, a colorless odorless gas resulting from combustion of fuel). CO detectors should be placed on each floor of the structure at eye level and should have an audible alarm and, when possible, a digital readout at eye level.
Chimney: A vertical shaft containing one or more passageways.
Factory-built chimney—A tested and accredited flue for venting gas appliances, incinerators and solid or liquid fuel-burning appliances.
Masonry chimney—A field-constructed chimney built of masonry and lined with terra cotta flue or firebrick.
Metal chimney—A field-constructed chimney of metal.
Chimney connector—A pipe or breeching that connects the heating appliance to the chimney.
Clearance—The distance separating the appliance, chimney connector, plenum, and flue from the nearest surface of combustible material.
Central cooling system—An electric or gas-powered system containing an outside compressor, cooling coils, and a ducting system inside the structure designed to supply cool air uniformly throughout the structure. 
Central heating system—A flue connected boiler or furnace installed as an integral part of the structure and designed to supply heat adequately for the structure.
Collectors—The key component of active solar systems and are designed to meet the specific temperature requirements and climate conditions for different end uses. Several types of solar collectors exist: flat-plate collectors, evacuated-tube collectors, concentrating collectors, and transpired air collectors.
High-low limit control—An automatic control that responds to liquid level changes and will shut down if they are exceeded. 
Primary safety control—The automatic safety control intended to prevent abnormal discharge of fuel at the burner in case of ignition failure or flame failure.
Combustion safety control—A primary safety control that responds to flame properties, sensing the presence of flame and causing fuel to be shut off in event of flame failure.
Convector—A radiator that supplies a maximum amount of heat by convection, using many closely spaced metal fins fitted onto pipes that carry hot water or steam and thereby heat the circulating air.
Conversion—A boiler or furnace, flue connected, originally designed for solid fuel but converted for liquid or gas fuel.
Damper—A valve for regulating draft on coal-fired equipment. Generally located on the exhaust side of the combustion chamber, usually in the chimney connector. Dampers are not allowed on oil- and gas-fired equipment. 
Draft hood—A device placed in and made a part of the vent connector (chimney connector or smoke pipe) from an appliance, or in the appliance itself. The hood is designed to a) ensure the ready escape of the products of combustion in the event of no draft, back draft, or stoppage beyond the draft hood; b) prevent backdraft from entering the appliance; and c) neutralize the effect of stack action of the chimney flue upon appliance operation.
Draft regulator—A device that functions to maintain a desired draft in oil-fired appliances by automatically reducing the chimney draft to the desired value. Sometimes this device is referred to in the field as air-balance, air-stat, or flue velocity control or barometer damper. 
Fuel oil—A liquid mixture or compound derived from petroleum that does not emit flammable vapor below a temperature of 125°F (52ºC).
Heat—The warming of a building, apartment, or room by a furnace or electrical stove.
Heating plant—The furnace, boiler, or the other heating devices used to generate steam, hot water, or hot air, which then is circulated through a distribution system. It typically uses coal, gas, oil or wood as its source of heat.
Limit control—A thermostatic device installed in the duct system to shut off the supply of heat at a predetermined temperature of the circulated air.
Oil burner—A device for burning oil in heating appliances such as boilers, furnaces, water heaters, and ranges. A burner of this type may be a pressure-atomizing gun type, a horizontal or vertical rotary type, or a mechanical or natural draft-vaporizing type.
Oil stove—A flue-connected, self-contained, self-supporting oil-burning range or room heater equipped with an integral tank not exceeding 10 gallons; it may be designed to be connected to a separate oil tank.
Plenum chamber—An air compartment to which one or more distributing air ducts are connected.
Pump, automatic oil—A device that automatically pumps oil from the supply tank and delivers it in specific quantities to an oil-burning appliance. The pump or device is designed to stop pumping automatically if the oil supply line breaks.
Radiant heat—A method of heating a building by means of electric coils, hot water, or steam pipes installed in the floors, walls, or ceilings.
Register—A grille-covered opening in a floor, ceiling, or wall through which hot or cold air can be introduced into a room. It may or may not be arranged to permit closing the grille.
Room heater—A self-contained, freestanding heating appliance (space heater) intended for installation in the space being heated and not intended for duct connection.
Smoke detector—A device installed in several rooms of the structure to warn of the presence of smoke. It should provide an audible alarm. It can be battery powered or electric, or both. If the unit is battery powered, the batteries should be tested or checked on a routine basis and changed once per year. If the unit is equipped with a 10-year battery, it is not necessary to replace the battery every year. 
Tank—A separate tank connected, directly or by pump, to an oil-burning appliance.
Thimble—A metal or terra cotta lining for a chimney or furnace pipe.
Valve (main shut-off valve)—A manually operated valve in an oil line used to turn the oil supply to the burner on or off.
Vent system—The gas vent or chimney and vent connector, if used, assembled to form a continuous, unobstructed passageway from the gas appliance to the outside atmosphere to remove vent gases