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Glossary of Heating and Insulation Terms




Air to Air Heat Exchangers-A mechanical ventilation system which preheats cold incoming air by transferring to it heat from the warm outgoing air. Used to maintain the energy efficiency of a structure while exhausting indoor air.

Air Turbine-Attic ventilator with attached blades which allows prevailing winds to spin turbine, and increases the volume of air removed from attic space.

Automatically Retractable Door Bottom Closure-A form of weather-stripping that is spring loaded so that it will seal the door bottom when door is closed, but will retract as the door is opened to prevent dragging on floor or carpet.

Clock Setback Thermostat-A device regulating the demand on the heating or cooling system by automatically switching from one temperature or control level to another.

Conditioned Space-The space within a building which is heated or cooled by an active space heating system.

Conduction-The direct transfer of heat through building elements such as walls, ceilings, floors, and windows. This is a major area of home heat loss.

Convection-The transfer of heat energy by air or fluid movement. This motion is a spontaneous circulation due to the combined actions of gravity and changes in air or fluid density. In space heating, the operation of a baseboard heater is a good example of convection.

Coverage Label-The label from a bag of loose fill insulation describing the size of area, depth, weight, and R-value that the material will provide.

Cross Ventilation-Placement of vent openings so that air flows in one vent, over insulated space, and out the other. In attics, a combination of eaves and ridge or high gable vents is best for cross-ventilation, because this takes advantage of natural convection.

Dead Air-Air trapped between two infiltration-free spaces which serves as a good insulator. This insulating principle is usually applied in storm doors and windows.

Dehumidifier-A mechanical device which removes moisture vapor from the air.

Finish Materials-A building material such as sheet rock or wood paneling exposed to the living space and used to contain or hide construction components.

Flame Spread Rating-used to indicate the rate at which flame will spread across the surface of a given material. The higher the number, the faster the flame spread.

Flashing-Sheet metal strips installed to prevent leakage over windows, doors, etc., around chimneys and other roof details.
Furring Strips-Strips of lumber affixed to a masonry wall to which insulating batts or blankets and gypsum board paneling can be affixed.

Ground Cover-Polyethylene sheeting used on the dirt floor of crawl spaces to prevent ground moisture from being drawn up into the house.

Infiltration-Outside air that enters a structure through openings or cracks in the construction materials, especially windows and doors. "Design" infiltration in residences can range from one-half air change to three air changes per hour, depending on how well the houses are constructed, caulked, or weather-stripped. Average air changes over the heating season are lower. Infiltration is a major area of home heat loss.

Interlocking Metal Weather-stripping-A two-piece unit comprised of a metal strip and interlocking metal retainer which creates an interlocking airtight seal when the door is closed.

Joists-Closely spaced parallel beams supporting a floor or ceiling.

Knee Wall-A short wall between an attic floor and sloping roof.

Knob and Tube Wiring-A wiring method using knobs and tubes for the support of simple insulated conductors, concealed in walls and ceilings.

Loose Fill-Insulation material (usually mineral wool, vermiculite, or cellulose) used for pouring or blowing into the space to be insulated.

Multi Track Windows-Operable storm window/main window combinations, usually purchased ready-made. Each window operates on a separate "track" in the sash. Sometimes incorporates a screen as well.

Net Free Area-The net area of a vent which provides free air access. This number is available on purchased vent fixtures and is determined by laboratory test. Weatherization program standards require 1 foot of net free air access (NFA) for each 150 square feet in attics insulated without vapor barriers and 1 square foot NFA for each 300 square feet in attics insulated with a vapor barrier.

Perimeter Insulation-Insulation installed on the sidewalls of a crawl space to reduce heat loss. Also protects plumbing in the space from freezing temperatures. Perimeter insulation should only be used at the express approval of your utility.

Perlite-A glossy volcanic rock which expands when heated. Processed perlite is used as loose fill insulation material or bound into slabs.

Perm-The unit of measurement of permeance of a substance to water vapor. The lower this number, the smaller the amount of water vapor that can pass through the membrane. See "Vapor Barrier."

Permeance-A measure of the transmission of water vapor through a material or combination of materials, measured in perms.

Prime Window-The original window to which a storm window or multiglazing is added to provide greater thermal resistance.

Radiation-The transfer of heat by direct rays traveling through space to a solid substance, but without heating the air (similar to light rays). Your body loses heat through radiation to cold windows and to cold uninsulated walls, ceilings, and floors. If walls themselves are cold, your house may be uncomfortable, even though the air temperature is as high as 75 or 80°

Recessed Fixture-Specialty lighting or exhaust fans installed flush with the ceiling, so that the back of the fixture extends into the attic. Recessed fixtures require special treatment in ceiling insulation. To avoid fire hazard, insulation must not come within 3 inches of the fixture.

Rock Wool-Thermal insulation material composed of threads or filaments of slag, produced by reprocessing the residual materials from metals smelting.

R Value-"R" stands for resistance to winter heat loss and summer heat gain and is more accurate than inches in designating insulation performance. Even though one type or brand of insulation is thicker or thinner than another, it will provide identical resistance to heat loss if the R-value is the same. R-values can also be added. If you now have R-11 attic insulation and you want R-30, you can add an insulation material rated at R-19.

Slab on Grade-Housing construction type having a concrete slab poured directly on the ground. The foundation extends below the frost line, and the slab forms the base for the building floor.

Thermal Break or Barrier-A non-metallic material positioned between metallic components of windows to prevent a direct path of heat loss through thermal conduction.

Vapor Barrier-A material which retards the transmission of water vapor. It is rated in perms ("permeance"). The smaller the perm rating, the better the water vapor resistance. A good vapor barrier should have a perm rating no greater than 1.0.

Vermiculite-An expanded mineral insulation consisting of a mica-like substance which expands when heated. The resulting granules are generally used as loose fill insulation.

Weather-stripping-Material such as vinyl, foam, or metal strips installed to seal small cracks around the moving parts of doors and windows. Weather-stripping is designed to block uncontrolled infiltration of cold air through these spaces and sometimes to repel wind-driven rain and moisture. The term weather-stripping often applies to caulking, a compound used to fill in joints and cracks in the house exterior.

Whole House Plenum-An enclosed (non-ventilated) and insulated crawl space used as a return or supply duct for a forced air heating/cooling system.


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