Boiler Room Definition/Terminology

There are many terms used in a discussion of boilers, the following is a list of some of the most common terms.


There is a glossary provided that covers some of the other terms that may be also used.

This section also contains some of the basic valves that are used on boiler and boiler systems, along with some of the common HVAC and piping symbols.

Boiler and Heating Terms

‘’‘BTU’’’ – British Thermal Unit; the amount of energy required to raise one pound of water one degree Fahrenheit.

1,000 BTU = 1 lb. of steam
150 BTU = 1 sq. ft. of hot water
34.5 lbs steam/hr = 1 boiler horsepower
1 boiler hp = 140 sq. ft. steam radiation
240 BTU = 1 sq. ft. of steam
34,500 BTU = 1 boiler horsepower
1 gallon of #2 oil = 140,000 BTU
1 cu. ft. LP gas = 2,550 BTU
1 cu. ft. natural gas = 1,000 BTU
1 KWH = 3,413 BTU
1 therm. natural gas = 100,000 BTU

‘’‘Boiler’’’- An enclosed vessel in which water is heated and circulated, either as hot water or as steam, for heating or power. A container, such as a kettle, is used for boiling liquids. In our context, a boiler is “a piece of heating equipment that is used to heat water for use in a hot water-based heating system.”

Examples of hot water-based heating systems include under-floor radiant heat, baseboard hot water, and radiator-based systems. A ‘‘furnace’’ is a piece of heating equipment that is used in a hot air-based heating system to heat the air that is circulated through the duct-work.

‘’‘Burner’’’- One that burns, especially:

  • A device, as in a furnace, stove, or gas lamp, that is lighted to produce a flame
  • A device on a stovetop, such as a gas jet or electric element that produces heat
  • A unit, such as a furnace, in which something is burned such as an oil burner
  • An incinerator

‘’‘AFUE’’’- Annual Fuel Utilization Efficiency, a standard government rating for energy efficiency.

‘’‘Air Conditioner’’’- A device used to decrease the temperature and humidity of air that moves through it.

‘’‘Anode Rod’’’- A sacrificial metal used to protect against corrosion in a hot water heater.

‘’‘Baseboard Heating’’’- Heating elements around the perimeter of a room used to give off heat produced by hot water circulating through them.

‘’‘Blower’’’- A unit used with a furnace to circulate air through a network of ducts.

‘’‘BTU/h’’’- (British Thermal Units per hour) a standard rating for heat transfer capacity.

‘’‘Cast Iron’’’- A durable metal with an exceptional capability to hold and transfer heat.

‘’‘Chimney Venting’’’- A vertical vent used to transfer exhaust products from a boiler or furnace to the outdoors.

‘’‘Combustion’’’- The process of converting fuel into heat; requires oxygen.

‘’‘Convective Heat’’’- The natural circulation of air across a heat source to heat the air.

‘’‘Direct Vent’’’- A boiler design where all the air for combustion is taken from the outside atmosphere and all exhaust products are released to the outside atmosphere, also known as sealed combustion.

‘’‘Draft Hood’’’- A device that prevents a back-draft from entering the heating unit or excessive chimney draw from affecting the operation of the boiler or furnace.

‘’‘Ductless Split A/C Systems’’’- A system that cools and dehumidifies air without the use of conventional duct work. The equipment location is split, with the condenser and heat pump outside of the home and the air handler and controls inside.

‘’‘Efficiency Rating’’’- The ratio of heat actually generated versus the amount of heat. Theoretically possible from the amount of fuel inputted.

‘’‘Flue’’’- The passageway that takes combustion exhaust from the combustion chamber to the flue collector and venting system.

‘’‘Forced Hot Air’’’- A furnace system using a blower to circulate air from within the home through the furnace and back into the home (as opposed to gravity circulation).

‘’‘Furnace’’’- An enclosure in which energy in a non-thermal form is converted to heat, especially such an enclosure in which heat is generated by the combustion of a suitable fuel.

‘’‘Heater’’’- An apparatus that heats or provides heat.

‘’‘Heat Exchanger’’’- The part of the boiler or furnace used for transmitting heat from the flame to air or water for heating.

‘’‘Heat Transfer’’’- The transmission of heat from the source (flame) to air or water.

‘’‘Heating Capacity’’’- The amount of usable heat produced by a heating unit.

‘’‘High-boy’’’- A term used to describe a furnace which has a small “footprint” but is tall. The blower is under the heat exchanger.

‘’‘Hot Water Boiler’’’- A heating unit that uses water circulated throughout the home in a system of baseboard heating units, radiators, and/or in-floor radiant tubing.

‘’‘Hot Water Heater’’’- A unit with its own energy source that generates and stores hot water.

‘’‘Hydronics’’’- The science of heating or cooling with water.

‘’‘Indirect Hot Water Storage Tank’’’- A unit that works in conjunction with a boiler to generate and store domestic hot water, it does not require its own energy source.

‘’‘In-Floor Radiant Tubing’’’- Tubing, typically plastic or rubber, used in conjunction with heated boiler water to heat floors.

‘’‘Low-boy’’’- A term used to describe a furnace that has a low profile. The blower is located on the same level plane as the heat exchanger.

‘’‘Low Water Cut-off’’’- A device used to shut down a boiler in the event of a low water condition exists.

‘’‘Natural Gas’’’- Any gas found in the earth (e.g., methane gas) as opposed to gases which are manufactured.

‘’‘Oil Heating’’’- The production of heat by burning oil.

‘’‘Propane’’’- A manufactured gas typically used for cooking or heating.

‘’‘Push Nipples’’’- Metal sleeves used to join adjacent sections of a boiler.

‘’‘Radiant Heating’’’- The method of heating the walls, floors, or ceilings in order to transfer heat to the occupants of a room.

‘’‘Radiator’’’- A heating element, typically metal, used in conjunction with water or steam to give off heat.

‘’‘Safety Shut-off Device’’’- Any device used to shut down a heating appliance in the event an unsafe condition exists.

‘’‘Sealed Combustion’’’- A boiler design where all the air for combustion is taken from the outside atmosphere and all exhaust products are released to the outside atmosphere, also known as ‘‘direct vent’’.

‘’‘Steam Boiler’’’- A heating unit designed to heat by boiling water, producing steam, and circulating it to radiators or steam baseboard units throughout the home.

‘’‘Stack Damper’’’- A device installed in the venting system that will automatically close when the appliance shuts down.

‘’‘Supply Tapping’’’- Opening in a boiler by which hot water enters the heating system.

‘’‘Tankless Heater’’’- A copper coil submerged into the heated boiler water used to transfer heat to domestic water.