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Glossary of Terms      
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Absolute Humidity or Humidity Ratio – The mass of water divided by the mass of air containing the water vapor.

Absorption – The process by which a fluid or a gas is taken into the interstices of a porous substance and held there.

Adsorption – The process by which gases adhere to solid surfaces.  The strength of the bond depends on the Van Der Waal forces between the gases and the solid.

Air Handler – The indoor part of a central air conditioning or heat pump system that moves cooled or heated air throughout the ductwork of your home. An air handler is usually a furnace or a blower coil.

Aerosol – An assemblage of small particles, solids or liquid, suspended in air.  The diameter of the particles may vary from 100 microns down to 0.01 microns. Examples: Dust, smoke, fog.

AFUE – Annual Fuel Utilization Efficiency. A measure of a furnace's heating efficiency. The higher the AFUE percentage, the more efficient the product. The US government's established minimum AFUE rating for furnaces is 78%.

Agglomeration – The formation of a larger airborne particle by the collision of two or more smaller particles.  Agglomeration takes place when attractive forces between the particle is greater than the kinetic energy of collision.

Air – The mixture of gases that makes up the atmosphere.  Air is composed of 78% nitrogen and 21% oxygen.  The balance consists of smaller amounts of gases that vary with location in which the air is sampled. 

Air Barrier – Any material used as to block the flow of air.

Air Change – A measure of the amount of air moving into and out of a space because of leakage of mechnical ventilation.  One air change is a volumetric flow of air equal to the cubic content of the space.  If a space has a cubical content of 10,000 cubic feet and the ventilation rate is 1000 cfm, 0.1 (1000/10,000) air change is occurring every minute, or 6 (60 x 0.1) air changes are occurring per hour.

Air Change Per Hour (ACH) – The amount of air that is changed out per hour.

Air Change Rate – The number of times in one hour that the air is replaced in a space.  Unit: air changes per hour (AC/h). 1 AC/h is the air flow rate in 1 hour that would move a volume of air equal to the space.

Air Flow – Quantity of air (cfm) passing through a given cross sectional area (sq ft) at a stated velocity (fpm).

Air, Combustion – The air mechanically removed to the outdoor from a space by such devices as kitchen fans, dryers, central vacuum cleaners, and not reused.

Air, Exhaust – The air mechanically removed to the outdoors from a space by such devices as kitchen fans, dryers, central vacuum cleaners, and not reused.

Air, Flue Gas Dilution – The ambient air that is admitted to a venting system at the draft hood, draft diverter or draft regulator.

Air Leakage – The uncontrolled exchange of air between the interior and exterior environments through unintentional openings in the building envelope under the influence of wind and buoyancy (Stack Effect) pressures.  Infiltration and exfiltration are both components of air leakage. 

Air, Make-up – Outdoor air supplied to replace exhaust air, e.g., by infiltration, make up air duct, supply fan, etc.  It does not include air entering the house as combustion air or to replace exfiltration air.

Air, Outdoor – Air from external atmosphere, not previously circulated in the building.  It is usually less contaminated than indoor air.

Air, Recirculation – Air removed from a space and returned heated, cooled, humidified, etc.

Air, Relief – Air mechanically removed, passively exiting, or exfiltrating from the house to reduce mechanically induced pressurization. (Opposite of make-up air)

Air, Return – Recirculation air being removed from a space.

Air, Supply – Recalculating air, with or without mixed ventilation air injected into a space.

Air / Vapor Barrier – Any material used to block the flow of air and water vapor.

Air, Ventilation (Supply) – Outdoor air intentionally supplied by mechanical means to a conditioned space.

Allergen – A biological or chemical substance that causes an allergic reaction. Common allergens include pollen, animal dander, dust and dust mites.

Apparent Sensible Effectiveness (ASE) – The term used in the CSA C439M standard for testing HRVs to describe the temperature rise of the outdoor air passing through an HRV.  The effectiveness includes the effect of motor heat gain, cross leakage gain and casing gain.  It is usually numerically higher than the sensible recovery efficiency of the HRV.  When the flows of indoor and outdoor air through the HRV are equal, the sensible recovery efficiency equals the temperature rise of the outdoor air divided by the temperature difference between the outdoor air entering the HRV and is expressed as a percentage.

Appliance (Heating) – A device to convert energy from fuel into heat energy, and includes any component, control, wiring, piping or tubing required to be part of the device. 

Approved – Acceptable to the authority having jurisdiction.

ASHRAE – American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc., (Atlanta, Georgia).

ASPE – American Society of Plumbing Engineers

Aspect Ratio – The ratio of the width to the depth of a duct.

ASSE – American Society of Sanitary Engineering

ASTM – American Society of for Testing and Materials

Asthma – A usually chronic inflammatory disorder constricting the airways characterized by difficulty in breathing.

B-Vent – A labeled, double-walled sheet metal chimney assembly.  Consisting entirely of factory-made parts, designed as “class B” according to the Gas Installation Code CGA B149.

Backdrafting (Back Spillage) – Flow reversal in a flue serving a fuel-fired appliance: the combustion products normally flowing up the flue are forced to reverse their course and discharge into the space occupied by the appliance.

Bacteria – Single-celled microorganisms ranging from harmless and beneficial to intensely virulent and lethal.

Barometric Damper – See Draft Regulator.

Blower – A fan used to force air under pressure.

Boiler – An appliance supplying hot liquid or vapor.

British Thermal Unit (BTU) – The quantity of heat required to raise the temperature of 1 pound of water 1 Fahrenheit degree.

1 Btu/h = 0.2931 Watts
1 Watt = 3.413 Btu/h

Brownian movement – The continuous zig-zag motion of particles (aerosols) in suspension.  The motion is caused by impact of molecules of the fluid (air) upon the particles.

BTU - That's the amount of heat required to raise one pound of water by one degree Fahrenheit. What that means is the higher the BTU rating, the more heating capacity of the equipment.

Building Envelope – The surface formed by all components of the building which enclose the conditioned space.

Burner – A device for the introduction of fuel, with or without air oxygen, into the combustion zone for ignition.

• Natural draft – The burner is not equipped with a fan or blower.
• Fan assisted – The combustion air is supplied by mechanical devices such as a fan or a blower at sufficient pressure to overcome the resistance of the burner only.
• Forced Draft – The combustion air is supplied by a mechanical device such as a fan or blower at sufficient pressure to overcome the resistance of the burner and the appliance.

Carbon Monoxide – An odorless, poisonous, flammable gas produced when carbon burns with insufficient air. We install Carbon Monoxide detectors.

Certified – Identified by a designed testing organization, recognized by the Standards Council of Canada and conforming to recognized standards or acceptable test reports.

CADR – Clean air delivery rate. A system of rating portable air cleaning devices.

CFM – Cubic feet per minute, a measure of airflow.  1 cfm = 0.472 L/s or conventionally 1 cfm = 0.5 L/s. A standard measurement of airflow.

CFS – Commercial Fact Sheet

Chimney – A primarily vertical shaft enclosing at least one flue.

Circulation Fan – Usually the main furnace blower in a forced air system.  Can be any ducted fan used to distribute recirculation air throughout the house.  When the ventilation system is coupled to the forced air system this blower is required to be operable independently of the furnace heating and cooling cycle.

Closed Loop System – Is where the water system is on the downstream side of a backflow prevention valve, pressure relief valve, check valve or other device that permits the flow of water only in one direction.

Coaxial Vent – A combustion appliance venting system consisting of an inner pipe exhausting products of combustion within an outer pipe drawing in combustion air.

Combination Forced Air and Domestic Water Heating System – A system that supplies potable hot water for space heating and domestic potable hot water.

Combustion Products or Gases – The constituents resulting from combustion of fuel with the oxygen of the air and includes inert gases that are part of the air, but not excess air.

Comfort Zone – The range of effective temperature over which a majority (50% or more) of adults feel comfortable.

Compressor – The part of the outdoor air conditioner or heat pump that compresses and pumps refrigerant throughout the system.

Condensation – The process of changing a vapor into a liquid by the extraction of latent heat.

Condenser Coil – The outdoor portion of an air conditioning or heat pump system that serves as a heat transfer point for dispelling heat to the outside air, as in an air conditioner or heat pump in the summer; or for collecting heat from the outside air, as in a heat pump in the winter.

Conditioned Space – Any interior portion of the building that is intended to be heated, cooled or ventilated.

Conductance, Thermal – The time rate of heat flow through unit area of a body, per unit temperature difference.  Often called U-Value
Units: Btu/(h ft2 F) or W/(m2 C)

Conduction Thermal – The process of heat transfer through a material from the hotter side to the cooler side.

Convection – The transfer of heat that takes place within moving gases and liquids.  An example is the heat carried by air after it has passed over a heating coil or heat exchanger in a heating unit.  In a cavity in a wall, air heats and expands next to the warmer side, becomes lighter and rises.  It is continuously replaced by a flow of cooler air from the opposite side.  When the warmed air reaches the cooler side, it passes heat to the surface there and the circulation continues.

Crawl Space – A shallow space below the living quarters of the basementless part of a house, normally enclosed by the foundation wall.

CSA – Canadian Standards Association, (Rexdale, Ontario).

Cubic Feet Per Minute (cfm) – Imperial unit of airflow. 1 cfm=0.472 L/s and 1 L/s = 2.12 cfm.  In common practice, using 1 cfm = 0.5 L/s and 1 L/s = 2 cfm is close enough, though the error is technically 6%

Damper – A valve or plate regulating the flow of air in a duct. Device in duct work regulates airflow. Effective in controlling airflow for zoning.

Dander – Small scales of animal skin. 

db – Decibel, a measure of sound.

Degree Day – For each day with a mean temperature below 65 degrees F (18 C) the number of degree-days is this difference.  These can be added up for a month of for a heating season.  Used in calculating heating energy consumption.

Delta T- The temperature difference across a building component.

Design Temperature – The temperature used for sizing heating or cooling equipment.  When actual temperatures go beyond the design temperatures, and there is no excess capacity in the equipment, thermal momentum will carry the building through these conditions for short periods, or a small degradation of comfort conditions can be expected.

• Winter Design Temperature – based on a 10 year average, the lowest sustained temperature that might be expected in normal winter conditions.  The coldest month is January and 2.5 % of the time in January the outdoor temperature may fall below the design temperature, but usually for only a short time.
• Summer Design Temperature – based on a 10 year average, the highest sustained temperature that might be expected in normal summer conditions.  The warmest month is July and 2.5% of the time in July the outdoor temperature may rise above the design temperature, but usually for only a short time.
• Design Temperature Difference – the difference between the indoor design temperature and the outdoor design temperature.

Dew Point – The saturation temperature at which condensation of water vapor to visible water takes place.  An example is the sweating on a glass of ice water.  The cold glass reduces the air temperature below its dew point, and the moisture that condenses forms beads of water on the glass surface.

Diffuser – The slotted or bladed guard at the room end of a branch duct, which may be equipped with a means of adjusting the aim of the flow of air.

Direct Vent – Applies to a type of fuel-fired appliance that takes its combustion air directly from the outdoors via a sealed passageway, and ejects its combustion gases outdoors as well, through an independent sealed vent, without ever using the indoor air of the building for combustion or venting.

Distribution Effect – An increase to the stack effect resulting from the depressurization of the basement due to return air being sucked into leaks in a joist distribution system or through basement return air inlets.

Draft – (1) The pressure difference which causes a current of air or gases to flow through a flue, chimney, heater or space.
(2) The flow of air, or combustion products, or both, through an appliance and its venting system.

(3) An uncomfortable localized feeling caused by one or more factors of high air velocity, low ambient temperature, or direction of airflow, whereby more heat is withdrawn from a person’s skin than is normally dissipated.

Draft Hood – A draft control device having no moveable or adjustable parts.  It may be built into or attached to an appliance or made part of a vent connector, and is designed to:

• (1) Assure ready escape of flue gases from the combustion chamber if there is either no draft or stoppage downstream of the draft hood.
• (2) Prevent a back-draft from entering the combustion chamber of the appliance.
• (3) Reduce the effect of stack action of a a chimney or vent, when the appliance operates.

Draft, Induced – A Mechanical draft where the fan or blower is is in the flue gas stream.

Draft, Mechanical – A draft produced by a mechanical device such as a fan, blower, or aspirator.

Draft, Natural – A draft where the combustion air is supplied from within the building and the products of combustion are conveyed to the outdoors through a chimney or B-vent.  This type of draft relies on thermal buoyancy to vent the combustion products.  The upward force created by the buoyancy must be greater than any resisting forces in the building envelope.  The force generated by the thermal buoyancy is proportional to the difference between the outdoor temperature and the flue gas temperature.  This type of draft may be reversed, resulting in combustion spillage if there is excessive negative pressure in the house or insufficient flue gas temperatures.

Draft Regulator (Barometric Damper) – A draft control device intended to stabilize the natural draft in an appliance by admitting room air to the venting system.  A double-acting draft regulator has a balancing damper free to move in either direction.

Dry Bulb Temperature – The temperature of air indicated by an accurate thermometer.  This is the usual temperature to which people refer, but it is called “dry bulb” when it is necessary to distinguish it from wet bulb temperature.  These two temperatures are required for accurate calculation of relative humidity.

Duct, Branch – A passageway carrying air to or from only one register or grill.

Duct, Trunk – A passageway carrying the air to or from two or more branch ducts.

Ductwork – The method by which air is channeled from the furnace or the blower coil throughout your home.

Dust – An aerosol of particles of any solid material, usually with particle sizes less than 100 microns.

Effective Length – In duct design, the length of a particular duct system path is equal to the total of the actual duct length and the equivalent lengths of the fittings in the flow path. 

Enclosure – A secondary room within or attached to a building in which an appliance is installed.

Equivalent Length – The length assigned to a duct fitting, expressed as the number of feet of straight smooth round duct of the same diameter as the fitting, which would have the same resistance airflow.

Equivalent Temperature Difference – For cooling load calculations, the actual temperature difference across an opaque building assembly modified for the effect of the sun, according to the assemblies orientation, material, color, and time of day.

Evaporation – The process of changing a liquid into a vapor by adding latent heat.

Evaporator Coil – The part of a heat pump or air conditioning system that is located inside the house in the air handler. It is here that the refrigerant evaporates as it transfers heat from the air that passes over the coil.

Feet per Minute – Imperial unit of air velocity.  1 fpm = 0.00508/s and 1 m/s =196.9 fpm.  In common practice, using 1 m/s = 200 fps is close enough, as the error is only about 1.6%

First Hour Rating – Amount of hot water that the water heater can supply in the first hour of operation; a combination of how much water is stored in the water heater and how quickly the water heater can heat cold water to the desired temperature.

Fixture – A receptacle, plumbing appliance or other device that discharges sewage or clear water waste and includes a floor drain.

Flue – An enclosed passageway for conveying flue gases.

Flue Effect – The infiltration caused by the suction created by the rapid rising of combustion gases in a chimney using natural draft.

Flue Gases – These are combustion products and excess air.

Florescent – A light source which provides light from an electrically excited element but relatively cool coating.

Formaldehyde – A colorless, pungent gas used in solution as a strong disinfectant and preservative and in the manufacturing of synthetic glues.  A VOC and known carcinogenic. 

Furnace – An indirect-fired, flue connected, space heating appliance, using warm air as the heating medium, and usually having provision for the attachment of ducts.

Furnace Room – An enclosed space that contains a furnace and usually separates an open basement from the furnace.

GAMA – Gas Appliance Manufacturers’ Association

Grade – The lowest of the average levels of finished ground adjoining the exterior wall of a building.  Localized depressions such as for vehicles or pedestrian entrances needs not be considered in the determination of average levels of finished grade. 

Grille – The slotted guard at the room end of a branch duct.  Usually non adjustable, and spoken in reference to return air ducts.

Habitable Space – Space designed for human occupancy, such as a bedroom, living room, dinning room, kitchen, family room, recreation room, or den.

Head Drop – The vertical distance between the lower edge of an eave and the top edge of the outer surface of the window glass.  This is the vertical component which, with overhang, determine shading of a window.

Heat Exchanger – Located in the furnace, the heat exchanger transfers heat to the surrounding air, which is then pumped throughout the home.

Heat Loss Factor (HLF) – For Basements, a factor relating heat loss to the temperature difference and to dimensions which depend on the part of the building envelope being considered.  For walls below grade, its units are Btu/(h ft F) or W/(m2 C), where the area is the area of the below grade floor.
These factors come from tables which take into account the depth below grade and the insulation added to the bare wall.

Heat Pump – An HVAC unit that heats or cools by moving heat.

Heat Reclaimer – A device installed externally or internally to a venting system to extract heat from flu gases.

Heat Recovery Ventilator (HRV) – A factory assembled unit incorporating a means to circulate air for ventilation and a means to transfer heat between the incoming and outgoing air streams.

Heat Transfer Multiplier (HTM) – The unit of measure that determines how many Btu’s will pass through one square foot of building material for a given design temperature difference.

HEPA – High efficiency particulate air (filter). Certified HEPA filters must achieve an efficiency of 99.97% for particles down to 0.3 microns.

Hood – A terminal in the exterior wall, floor or roof for the outdoor air inlet or the exhaust air outlet.

HRAI – Heating, Refrigeration, and Air Conditioning Institute of Canada.

HSPF – Heating Seasonal Performance Factor. A measure of heat pump heating efficiency. The higher the rating, the more efficient the heat pump. The US government's established minimum HSPF rating for furnaces is 6.8%.

Humidifier – Equipment that injects moisture into heated air as it passes from the furnace into the ductwork to be distributed throughout the home.

HVAC – Heating, Ventilation, and Air Conditioning.

HVI – Home Ventilating Institute, Illinois.

IAQ – Indoor Air Quality.

IDT – Indoor Design Temperature.

Impingement – The process in which particles are removed from an air stram because of their inertia. As air containing a particle flows towards a filter fiber or other collecting surface, the particle does not follow the air streamlines because of its inertia.  Instead it moves in a straight line colliding with the filter fiber or surface to which it may become attached.

Incandescent – A light source which provides light from a white-hot electrically heated filament.

Inches Water Column (or Gauge) – A measure of small pressure differences, equivalent to that obtained by observing the differences in height of the water levels in a u-tubewhose ends are connected to the places having different pressures.  Unit: in w.c. or Pa 1 in w.c. = 249 Pa, or, conventionally, 1 in w.c. = 250 Pa.

Interception – The process in which a particle is removed from the air stream as it follows the streamlines around a fiber.  The particle comes in contact with a fiber and stays attached to it because the attractive forces between the fiber and the particle are stronger than the forces of disruption of the moving air stream. 

Interpolation – Finding a value from a table or list when the value used for reference falls between a pair of reference values of the table.

Laminar Flow – A predictable parallel flow of air particles in a duct, occurring only at very low velocities, and offering less resistance than turbulent flow.

Latent Heat – The energy involved in a change of state without a change in temperature.  For example, to evaporate 1 Lb of water to water vapor takes 970 Btu and condensing 1 Lb of water vapor to water will release 970 Btu.  All this happens while the temperature remains steady.

Liters per Seconds (L/s) – Metric unit of airflow. 1 L/s = 2.12 cfm  and 1 cfm = 0.472 L/s.  In common practice, using 1 L/s = 2 cfm and 1 cfm = .5 L/s is close enough, though error is technically about 6%.

Minimum Ventilation Capacity (MVC) – In the CSA F326 standard, a capacity set by “room count”, ie, 10 cfm per room but 20 cfm for the master bedroom, and 20 cfm for a basement area exceeding 2/3 of the total basement area.

Micron – One millionth of a meter.  A micron is more correctly known as a micrometer.  There are 25,400 microns per inch. 

Mixed Air Temperature – When ventilation is used, the temperature of the mixture of the return air and outdoor air used for ventilation.

Mold – A fungus that grows on damp decaying organic matter.  It is characterized by a fuzzy mat surface. 

Natural Ventilation – Outdoor air supplied to a habitable space by natural forces through intentional openings such as open doors and windows, and by air leakage through unintentional cracks or holes.

Non-Packaged System – Consists of a water heater certified for use with potable water and space heating, air handler component and a heating coil not designed specifically for the air handler and supplied separately from the air handler. 

Odor – A quality of gases, liquids, or particles that stimulates the olfactory organ. 

Overhang- The horizontal distance an eave extends outward past the outer surface of the windows.  This is the horizontal component which with head drop determines shading of the window.

Ozone – A gas whose molecules are composed of three oxygen atoms.  Its symbol is O3.  It is an unstable gas that is significantly toxic.  The 1989 threshold level value for ozone was 0.1 parts per million for an 8 hour time weighted average.

Packaged Air Handler – A packaged unit which contains a blower, potable water coil and a manufactured specified circulator pump.

Packaged System – Consists of a water heater certified for use with potable water and space heating, and a packaged air handler.

Package Unit – An appliance supplied as a complete unit including controls and integral wiring.

Packaged Ventilator – A factory assembled unit which has means to supply ventilation air and/or to remove exhaust air, intended for continuous or intermittent operation, such as HRVs and Bath fans.

Particles – Very small solid or liquid substances that are light enough to float suspended in the air.

Partition – Any wall or floor separating conditioned zones or room in a building.

Potable – Fit for humane consumption.

Potable Water – Water fit for human consumption.

Potable Water System – The plumbing that conveys potable water.

Power Venter – A device to provide mechanical draft installed between the appliance and the vent termination.

Pre-engineered Package System – A certified system tested as a whole to supply, simultaneously, space heating and domestic water requirements.

Pressure Drop – The static pressure loss caused by airflow through a duct, filter coil, HRV core, etc.

Pressure External Static – The negative static pressure in a return air plenum that is interconnected with the positive static pressure in the supply plenum of a unit such that when they are added together, they become the total external static pressure of the unit.  The unit external static pressure is the motive force that the blower will exert, after overcoming the internal resistance of the internal components including the filter casing, to propel the air to be circulated through the supply and return air ducts.

Pressure, Negative (depressurization) – The condition of lower air pressure inside the house than outside.  It happens when the amount of air removed from the house exceeds the amount supplied by mechanical or other means.  Outdoor air is sucked in through openings in the building envelope, which may include the chimney.

Pressure, Positive (pressurization) – The condition of higher air pressure inside the house than outside.  It happens when the amount of air supplied to the house exceeds the amount removed by mechanical or other means.  Excess air is forced out through any openings in the building envelope.

Pressure Static – The pressure available between the inside and outside of a duct; a measure of pressure available from a fan to move a given amount of air or the pressure required to use or deliver a given amount of air across a resistance. 

Principle Exhaust Fan – A fan intended to be able to remove air from a home continuously.  An HRV can be a principal exhaust fan.

Radiation – The transmission of heat energy which occurs by means of electro-magnetic waves whenever two surfaces at different temperatures face each other.

Refrigerant Lines – Two copper lines that connect the outdoor air conditioner or heat pump to the indoor evaporator coil.

Register – The slotted guard at the room end of a branch duct, equipped with a damper or other means of regulating and or aiming the flow of air.

Relative Humidity (% RH) - When dealing with moisture issues, many people hear the terms relative humidity and dew point without fully grasping what they mean.  Relative humidity (RH) is the term most used to describe the percentage of water vapor that exists in a gaseous mixture of air and water.  A RH reading is a measure of the amount of water vapor present in the air compared with the amount of water the air can hold at the temperature at the time of measurement.  Relative humidity is expressed as a percentage and is calculated as follows:
RH = Actual vapor density/saturation vapor density x 100%

In plain English, the RH level tells you the percentage of water in the air.  When relative humidity is 100%, water vapor in the air will turn into rain, condensation, dew, snow or frost.  You can feel relative humidity on your skin because it is a measure of how much water vapor the air can hold before it turns to liquid.

Relative humidity is affected by temperature.  As temperature becomes colder, relative humidity will raise.  Relative humidity in a room may be 50%, but when you introduce a cold glass of water, the air around the glass gets cold and condensation forms on the cold surfaces.  What happens here is that relative humidity of air contacting the cold surfaces raises from 50% to 100% as water vapor turns to liquid.

Resistance Thermal – Often called R-Value, the reciprocal of thermal conductance. (ie, R= 1/U). Units: (h ft2 F)/Btu or (M2 C)/W. The resistance of adjacent components of an assembly, eg, a wall, may simply be added to find the total resistance of the assembly.  Heat loss or gain due to conduction is then the product of the area of temperature difference, divided bt the R-Value.

Return Air Ceiling Plenum – The space above the finished ceiling, and below the roof or floor above, used for the collection of air from the space below the ceiling for cycling through the conditioning system.

Safety Limit Control – A safety control intended to prevent an unsafe condition of temperature, pressure or liquid level.

SBS – Sick Building Syndrome.

SEER – Seasonal Energy Efficiency Ratio. A measure of cooling efficiency for air conditioners. The higher the SEER, the more energy efficient the equipment. The government's minimum SEER rating is 10.

Sensible Heat – Heat that will change the temperature of a substance without changing its state.  Sensible heat is measured with a thermometer.  Water that is heated from 68 F (20 C) to 95 F (35 C) does not change state. It remains a liquid.  Because this change in temperature can be read with a thermometer, the heat involved is sensible heat.  The reverse is also true: If water is cooled, the amount of heat removed is sensible heat.

Sensible Recovery Efficiency (SRE) – The term used in the CSA C439M Standard for testing HRV’s to describe the net energy recovery during the winter heating conditions.  It is corrected for the effect of motor heat gain, defrost energy, cross-leakage gain and other effects like casing gain.  It is usually numerically lower than the apparent sensible effectiveness of the HRV.

Shading Factor – A geometric factor, dependant on latitude and orientation, used to calculate the shading effect of an overhang on a window.

SI – The official international abbreviation of the name for the modern metric system of measurement.  It stands foe Le Systeme International d’Unites.

Single Package – A heating and cooling system contained in one outdoor unit.

SMACNA – Sheet Metal and Air Conditioning Contractors National Association.

Solar Corrections – An amount to be added (though the number is sometimes negative) to the cooling delta T to allow for the solar radiation effect and mass effect for walls and roofs.

Solar Heat Gain Factor – For cooling load calculations, a factor expressing heat gain per unit area across a glazed building assembly, according to the assemblies orientation, the construction of the building, and the time of day.

Solar Radiation – The energy arriving in a direct line from the sun in the form of light and heat, warming any object in its path.

Specific Heat – The quantity of heat required to change the temperature of a substance by one degree.  1 Btu is required to change the temperature of 1 Lb of water 1 F, or in the SI, 1.16 W is needed to change the temperature of 1 Kg of water 1 C.

Split System – A combination heat pump or air conditioner with indoor components such as a furnace or blower coil. Split systems should be matched for optimum efficiency.

Stack Effect – The tendency of warm air which has risen to the top in a building (because it is lighter) to escape through cracks and be replaced by cooler air from outside which infiltrates through lower openings.  The overall result is a continuous flow, which exfiltration occurring upstairs and infiltration occurring downstairs.  At some point, where the airflow changes from an outward to an inward direction, there is no pressure difference.  Between inside and outside.  This can be described as a flat surface cutting across the building and dividing it into two parts: one with high pressure and one with low pressure, relative to outdoors.  This dividing plane is known as the “neutral pressure plane”.

Supplemental Exhaust – The exhaust required in addition to the principal exhaust fan capacity (PEFC) to equal the total ventilation capacity (TVC).  It may be provided by one of more of a higher speed of the principal exhaust fan or the HRV, and/or by a kitchen range hood, or bath/water closet fans.

Supplementary Heating – Commonly used in finished basements and or basement walk out areas; may be supplied by any type of thermostatically controlled heating source.

Tankless Water Heater – Tankless water heaters are often referred to as, "on-demand water heating," because it does not store heated water. Once the faucet is opened, water flows into the heater where a sensor turns on the heat exchanger or heating coils. Water flows through the heating coils, it is heated to the desired temperature. Once the faucet is closed, the sensor automatically shuts down the heating coils. The entire process takes about 5 seconds to heat the water initially. They have advantages for saving money, continuous flow of hot water and longer life span. The disadvantages include limited flow of hot water for multiple outputs along with higher set up costs vs. traditional water heaters.

Terminal Velocity – For a diffuser, a velocity of about 50 fpm, used to define the extent of the throw of the diffuser.

Thermal Buoyancy – The result of a gas’s being warmer than a larger body of gas to which it is connected.  The warmer body of gas is lighter and will seek to rise relative to the larger body.  In houses it is evident in the action of natural draft chimneys and in stack effect.

Thermostat – Usually found on an interior wall, this device operates as a control to regulate your heating and cooling equipment so that you can adjust your home comfort at the touch of a switch.

Thermal Storage – The delayed release of heat absorbed from solar radiation (or other heating sources) by objects within a conditioned space and by the surface enclosing it.

Ton – Unit of measurement for determining cooling capacity. One ton equals 12,000 BTU/hr.

Total Pressure – Although non-existent pressure, this term expresses the sum of static and velocity pressures.

Total Ventilation Capacity – In the NBC, the minimum combined capacity of the ventilation system(s) installed, calculated by a “room count”.