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Glossary of Building Science & Energy Efficiency Terms:


AFUE – Annual Fuel Utilization Efficiency. AFUE is a measure of the fuel efficiency of a heating system. It takes into account normal operating losses such as start-up, standby, and cycling. The higher the AFUE rating, the more efficient the heating system is.

AHRI – Air-Conditioning, Heating, and Refrigeration Institute. AHRI is a trade association that uses third party testing and certifies the performance of different Heating, Ventilation, and Air Conditioning (HVAC) systems available in North America. A listing of products and their performance is available in the AHRI Directory (www.ahridirectory.com).

Argon – Argon is a gas used to fill the space between window glazing. Argon has a lower heat conductivity than air, and suppresses gas movement between the glazing. A window filled with Argon gas will reduce heat loss better than a window filled with regular air.

Asbestos – A fibre commonly found in many building supplies (), including insulation materials, such as vermiculite. If asbestos is exposed the fibres can become airborne in the interior of the home. Inhalation of asbestos fibres can lead to different forms of cancer and scarring of the lungs. Check Health Canada’s website for more information.

ASTT – Applied Science Technologists and Technicians of BC. It is BC’s independent certifying body for applied science technicians.


BTU – British Thermal Unit. A BTU is a unit for heat. It is used to measure the heat output of a heating system. One Btu is the amount of heat energy given off by a typical birthday candle.


Chlorofluorocarbons (CFCs) – CFCs are ozone depleting chemicals. Older appliances that use refrigerant (freezer, refrigerator, heat pump, etc.) are common sources of CFCs and need to be recycled properly to prevent CFCs from being released into the atmosphere. Visit ENERGY STAR® for more information.

CFL – Compact Fluorescent Lamp (or Light). CFL bulbs are rated to last up to 10 times longer and use around 70% less energy than regular incandescent bulbs.

Combustion Spillage – Oil, wood, or gas burning appliances produce heat by burning fuel. Burning fuel produces combustion gases, which are normally vented to the outdoors through a chimney or vent pipe. Combustion spillage is the unwanted flow of combustion gases into the home. Combustion spillage (also known as backdrafting) occurs when a home becomes depressurized, and harmful combustion gases (such as carbon monoxide) are sucked back into the home through vents or a flue. Depressurization can happen when a home is very air tight and all exhaust fans, such as range hoods, bathroom fans, the dryer etc. are running at the same time, drawing air from the inside to the outside of the home. To learn more about combustions spillage, visit Natural Resources Canada’s website.

Conduction – Conduction occurs when heat moves through a material or building assembly (e.g. a wall). For example, the heat from a cast iron frying pan is transferred to the handle and eventually to your hand. Insulation reduces heat loss due to conduction.

Convection – Convection is the movement of heat through fluids such as water or air due to the temperature and density differences within the fluid. For example, warm air is lighter and will rise to the top while relatively cooler air will be heavier and fall to the bottom, creating a convection current. Drafts next to windows can be attributed to convection currents.

COP – Coefficient of Performance. COP is a measure of a heat pump’s efficiency. The COP is determined by dividing the energy output of the heat pump by the electrical energy needed to run the heat pump at a specific temperature. The higher the COP, the more efficient the heat pump.


Detached Home – A home where the walls and roofs are independent of any other building (i.e. not attached to any other building).

Dehumidistat – A device that monitors and maintains the set or preferred relative humidity in the air. If humidity levels rise above the level that you’ve set, the dehumidistat will automatically turn on an exhaust device such as a bathroom fan, to remove excess moisture from the home.


EnerGuide – The official mark of the Government of Canada for its energy performance rating and labeling programs for housing and energy-using products. The EnerGuide label allows consumers to find the most efficient products and homes.

EnerGuide Rating – The energy performance rating of a house, stated in gigajoules per year, determined using standard operating conditions and calculated by subtracting the annual renewable energy contributions from the annual energy consumption. Homeowners will receive an EnerGuide Rating after completing an EnerGuide home evaluation.

Energy Factor (EF) – An efficiency rating of gas- or oil-fired storage tank-type or tankless water heaters, where energy supplied as hot water is divided by the total amount of energy used by the water heater over a 24 hour period taking into account standby loss, cycling and recovery efficiency. The higher the EF, the more efficient the water heater. ENERGY STAR® – ENERGY STAR is an international symbol for energy efficiency – a simple way for consumers to identify products that are among the top energy performers on the market. ENERGY STAR qualified products help save energy and money, and protect the environment. To qualify for the ENERGY STAR symbol, products must meet stringent specifications for energy consumption without sacrificing the features, versatility and quality expected of high-performing products.

Existing Home – A house that is older than 6 months, based on the date of occupancy by the first homeowner.

Exposed Floor – Exposed floors are floors that hang over an unheated space, and are exposed to outdoor temperatures. For example, an overhanging floor such as that found in a bay window or the floor over a garage are defined as exposed floors.


Fenestration – Refers to all types of windows and doors, and their components (sash, frame, and glazing).


Gigajoule (GJ) – A unit of energy. One GJ is equivalent to 278 kilowatt-hours (kWh) of electricity, 27 m3 of natural gas,  39 L of propane, and 26 L of residential fuel oil. The EnerGuide Rating is expressed in Gigajoules per year.

Glazing – The panes of glass incorporated into a window unit. Single-glazed refers to a single pane window double-glazed refers to two panes of glass; triple-glazed refers to three panes of glass. Glazing often have a low-e coating(s) to improve its energy performance of the window.


HRAI – The Heating, Refrigeration and Air Conditioning Institute of Canada. HRAI is a non-profit national trade association of manufacturers, wholesalers, and contractors to the heating, ventilation, air-conditioning and refrigeration industries. It advocates a safe, responsible, and fair industry where systems are designed, installed, and serviced by qualified professionals.

HSPF – Heating Seasonal Performance Factor. A measure of the total heat output in Btu of a heat pump over the entire heating season divided by the total energy in watt hours it uses during that time. The higher the HSPF rating, the more energy efficient the heat pump is for heating.

HVAC – Heating, Ventilation, and Air Conditioning. Refers to the different mechanical systems, machines and technologies used to maintain indoor air quality and temperature, such as heat pumps, furnaces, boilers, and mechanical ventilators. 


Kilowatt Hour (kWh) – a measurement of energy supplied by one kilowatt (kW) of power over a one-hour period. This unit is often used to measure the amount of electrical energy used by your home (see your electrical bill).


LED – Light Emitting Diode. LED light bulbs are more efficient than incandescent light bulbs because they require less power (watts) to produce the same amount of brightness (lumen) as standard incandescent bulbs. They have a low power consumption, low heat generation, and a much longer lifespan when compared to incandescent and compact fluorescent bulbs.

Low-e – Low-Emissivity. Low-e is a thin coating on window glazing that reduces the amount of solar heat permitted through the window, while still allowing visible light to pass through. Low-e coatings increase a window’s insulation value and make it more energy efficient.


Mobile Home – a movable dwelling unit designed and constructed to be transported by road on its own chassis to a site, and placed on a permanent foundation such as blocks, posts, or a pad.


New Home – A house that is six months old or less, based on the date of occupancy by the first homeowner.

NRCan – Natural Resources Canada. It is the Canadian ministry responsible for natural resources, energy, and others. NRCan administers the EnerGuide Rating System through the Office of Energy Efficiency. 


Photovoltaic – A photovoltaic cell is a device that generates power by converting light from the sun into electricity. Solar Panels are composed of photovoltaic cells that allow sunlight to energize electrons, which generates a flow of electricity. 


R-Value – Thermal Resistance Value. R-Value is the imperial system unit of measurement (ft2·°F·h/BTU) of a material’s thermal resistance (i.e. how good it is at resisting heat flow by conduction). The higher the resistance value, the slower the rate of heat transfer through the material. Insulation materials are measured in R-Value. To convert an R-Value to an RSI Value (metric system), divide the R-Value by 5.678.

RSI-Value – RSI-Value is the metric system unit of measurement (m2·K/W) of a material’s thermal resistance. To convert an RSI-Value to an R-Value, multiply the RSI-Value by 5.678.

Radiation – Radiation occurs when heat transfers from a warm object to a relatively cooler object by giving off heat waves in all directions. For example, heat energy from the sun or a heat lamp is in the form of radiant energy.

Radon – Is a colourless, odorless, radioactive gas that naturally occurs when uranium in soil and rock breaks down. It can seep into homes and cause an increased risk of developing lung cancer when inhaled. Read more about Radon on the Health Canada’s website.

Relative Humidity – The amount of moisture in the air compared to the maximum amount of moisture that the air could retain at the same temperature. Relative humidity is measured as a percentage and depends on the current air temperature. Dehumidistats connected to a ventilation system (often a bathroom fan) can help to keep indoor humidity at a comfortable level.

Row Home – A dwelling unit separated either by one vertical division wall, termed a “party wall,” from the adjacent dwelling unit (end unit); or by at least two vertical party walls from the adjacent dwelling units (middle unit). Townhouses are a form of row homes.


SEER – Seasonal Energy Efficiency Ratio. SEER measures the cooling efficiency of a heat pump over the entire cooling season. It is determined by dividing the total cooling provided (in Btu) over the cooling season by the total energy used by the heat pump during that time (in Wh).

Semi-Detached – A set of two dwelling units separated from each other by one vertical division called a “party wall.”

SHGC – Solar Heat Gain Coefficient – Measures the fraction of solar energy transmitted through windows. SHGC is measured on a scale of 0 to 1; values typically range from 0.25 to 0.80. The lower the SHGC, the less solar heat the window transmits.

Steady-State Efficiency – The maximum efficiency of a heating system after it has been running long enough to reach its peak operating temperature. It is expressed as a percentage.


TECA – Thermal Environmental Comfort Association. TECA provides British Columbia’s residential heating, ventilating and cooling industry with training programs.


UFFI – Urea-Formaldehyde-Based Foam Insulation. A Urea formaldehyde based foam insulation commonly used in homes built in the 1970’s. This type of insulation has been prohibited since 1980 as it is known to release formaldehyde gas during and after installation.

U-Factor – A measure of the rate of non-solar heat transfer through the window. The lower the U-factor, the greater a window’s resistance to heat flow and the better its insulating value. The U-factor is the inverse of the R-Value.


Vermiculite – A form of insulation which can be found in homes built prior to 1990. Some vermiculite insulation may contain asbestos fibres that can pose health risks when disturbed. Read more about the health risks of vermiculite and asbestos on Health Canada’s website.

Visible Transmittance (VT) – Measures the amount of light the window lets through. VT is measured on a scale of 0 to 1, with values generally ranging from 0.20 to 0.80. The higher the VT, the more light you see.


Watt – A measurement of power.