Home heating glossary

Up your heating know-how with our handy homeowner glossary of heating terminology

Annualized Fuel Utilization Efficiency. A measure of heating efficiency. The higher the AFUE of a boiler or furnace, the more efficient the system is.

Efficiency standards for heating and cooling units in the US are governed by the department of energy. Boilers and furnaces are rated by the AFUE ratio, which is the percent of heat produced for each dollar of fuel used. A boiler with an AFUE of 85 will turn 85% of its fuel into useable heat, while the other 15% of fuel is wasted through a number of factors. A heating unit with an AFUE rating over 90 is classified as “high efficiency.”

Radiators placed along the baseboards of a home’s walls. Hot water is pumped through the baseboards via pipes, and fins help dissipate heat throughout a room.

A system that heats water to make hot water or steam, which circulates through pipes and radiators, heating a home or other building.

British Thermal Unit. A measurement of heat energy. One BTU is the amount of heat required to raise one pound of water by one degree Fahrenheit.

BTU’s per hour (BTUh) is the benchmark used to estimate a heating system’s capacity. The higher the number of BTU’s a boiler is rated for, the larger the area it can properly heat.

Combined Annual Efficiency. The CAE is a measure of the amount of heat produced for every dollar of fuel used. It is used to compare efficiencies of integrated water and space heaters.

A compact, efficient unit that provides all heat and hot water for a smaller home or apartment.

A Combi boiler is like a standard unvented boiler, but they include a second heating circuit to quickly heat water on demand. Combi boilers do not store hot water like a traditional system, Instead, they heat water directly from the main as needed, which allows for unlimited hot water.

Water heaters fueled by gas or oil. They achieve high efficiency (typically greater than 90% on the higher heating value) by condensing water vapor in the exhaust gases and so recovering its latent heat of vaporization, which would otherwise have been wasted.

Department of Energy. The US DOE is a federal agency responsible for monitoring the consumption of energy sources, and setting industry efficiency standards for all US heating and cooling units.

A gas or oil-fueled boiler system that has been combined with a heat pump, alternating between two fuel sources to maximize comfort and efficiency.

A system of metal or synthetic tubes that are used to transport air from heating, ventilation, and air-conditioning equipment throughout your home.

A program of the US Environmental Protection Agency (EPA) designed to help consumers save money by choosing energy-efficient products and technologies.

Equipment that bears an ENERGY STAR® label meets or exceeds federal guidelines for energy-efficient performance. A product’s AFUE rating will be located on an ENERGY STAR® label.

A duct, pipe, or chimney into which combustion gases flow in order to be conveyed out of a home to the outdoors.

A system that heats and distributes air through a house’s ductwork.

A component inside a boiler or furnace that allows heat from a fluid (a liquid or a gas) to pass to a second fluid (another liquid or gas) without the two fluids having to mix together or come into direct contact.

A system that uses electricity to move heat from a cool area to a warm one, keeping a space warmer in the winter and cooler in the summer.

Home Energy Rating System. A nationally recognized energy rating program designed to calculate the energy efficiency of homes. This rating system allows homes to be rated and compared by home buyers and renters for energy efficiency.

Heating Seasonal Performance Factor. A heating efficiency rating for heat pumps. The higher the rating, the more efficient the pump. A rating of at least 8.2 will be awarded an ENERGY STAR® label.

Heating, Ventilation, and Air-Conditioning. An HVAC system will include products like boilers, air conditioners, ductwork, and thermostats, along with other products that provide home comfort.

An energy-efficient heating system that uses tubing to run hot water beneath the floor, along baseboards, or through radiators.

Hydronic heating is sometimes also referred to as “radiant heating.” The air temperature of a hydronically heated home or building may be lower than a conventionally heated home to achieve the same level of comfort.

A small flame used in gas appliances which are kept continuously alight to ignite the gas burners when needed by the appliance.

A thermostat with the ability to adjust home heating and cooling equipment according to a pre-set schedule.

Some “smart” thermostats offer smartphone apps to adjust or monitor heating and cooling equipment from remote locations, and others include sensors to know when people are home, allowing for temperature adjustment and energy savings.

A measure of a material’s thermal resistance, or resistance to the transfer of heat. R-Value is used to describe the heat resistant capabilities of insulation material. The higher the R-value of a material, the greater its heat resistant and insulating capacity.

A component of a radiant heating system that radiates heat from its surface into a room. The heat is usually supplied to the radiator through hot water or steam circulation.

A water heater with a tank that stores heated water to be dispensed when needed. Hot water is dispensed from the top of the tank and is refilled by cold water in the bottom of the tank.

A water heater that heats water on demand as needed as opposed to a storage water heater, which heats water and stores it for later use. Tankless water heaters are also called “demand water heaters.”

A unit of measurement for heat which contains 100,000 BTU’s