HVAC GLOSSARY - B

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Backdrafting: Reverse flow of combustion gases down the chimney of a vented combustion appliance, which is often caused by depressurization of the room where the appliance is located. A condition where the normal movement of combustion products from a combustion appliance up a flue is reversed so that the combustion products can enter the building.

Background Concentration: The level of a contaminant present before the introduction of a new source.

Balance Point: The lowest outdoor temperature at which the refrigeration cycle of a heat pump will supply the heating requirements. Usually, a temperature between 30°F to 45°F -- at which a heat pump's output exactly equals the heating needs of the house. Below the balance point, supplementary electric resistance heat is needed to maintain indoor comfort.

Balancing: The process of adjusting the flow of air in duct systems, or water flow in hot-water heating systems. Proper balancing is performed using accurate instrumentation to deliver the right amount of heating or cooling to each area or room of the home.

Bioaerosol: An airborne microbial contaminant, such as a virus, bacteria, fungus, algae, or protozoa, or particulate material associated with one of these microorganisms.

Biocide: Substances or chemicals that kills organisms such as molds.

Biological Contaminants: Agents derived from, or that are, living organisms (e.g., viruses, bacteria, fungi, and mammal and bird antigens) that can be inhaled and can cause many types of health effects including allergic reactions, respiratory disorders, hypersensitivity diseases, and infectious diseases. Also referred to as "micro biologicals" or "microbials."

Blower door: A large powerful variable-speed fan mounted in a doorway that blows air into (pressurizes) or sucks air out of (depressurizes) a house. It's used to test for air leakage in a house. The size and complexity of the fan varies, but all blower doors have adjustable frames around the fan so that they can fit snugly into most doorways.

Blower (Fan): An air handling device for moving air in a distribution system.

Boiler: A device for generating steam for power, processing, or heating purposes or for producing hot water for heating purposes or hot water supply. Heat from an external combustion source is transmitted to a fluid contained within the tubes in a boiler shell, a closed vessel in which water is converted to pressurized steam. This fluid is delivered to an end-use at a desired pressure, temperature, and quality.

Boot: A piece of duct used to connect ducts with registers.

Breathing Zone: The area of a room in which occupants breathe as they stand, sit, and lie down.

BRI (Building-Related Illness): Diagnosable illness whose symptoms can be identified and whose cause can be directly attributed to airborne building pollutants (e.g., Legionnaire's disease, hypersensitivity pneumonitis). Also: A discrete, identifiable disease or illness that can be traced to a specific pollutant or source within a building. (Contrast with "Sick building syndrome").

BTU (British Thermal Unit): The amount of heat that will raise or lower one pound of water 1 degree F. at 39.2 degrees F. One BTU is the equivalent of the heat given off by a single wooden kitchen match. The British Thermal Unit is a standard of measure for cooling and heating capacities. This is how the capacity of air conditioning is measured. A standard measure of heat energy in the U.S., commonly used to measure the energy content of various fuels and steam. It takes one Btu to raise the temperature of one pound of water by one degree Fahrenheit at sea level. For example, it takes about 2,000 Btus to make a pot of coffee. One Btu is equivalent to 252 calories, 778 foot-pounds, 1055 joules, and 0.293 watt-hours. Note: In the abbreviation, only the B is capitalized. For your home, it represents the measure of heat given off when fuel is burned for heating, or the measure of heat extracted from your home for cooling.

BTUH (British Thermal Unit Per Hour): Establishes a time reference to btu input or output rates. A BTUH is how many BTUs are used per hour.

Buffer zone: An area within the home between the conditioned zones and the outside. Thus, it normally is not conditioned (for instance, attics, attached garages, crawlspaces, basements, and enclosed porches).

Building Energy Efficiency Standards: California Code of Regulations, Title 24, Part 2, Chapter 2-53; regulating the energy efficiency of buildings constructed in California. Building, Envelope the outer walls, windows, doors, roof, and floors of a building; the building shell.

Building Envelope: Elements of the building, including all external building materials, windows, and walls, that enclose the internal space.