Tuesday, August 22, 2017
 
   
Support Glossary

Combustion Appliances and Combustion Safety Testing Terms

Air-Free Carbon Monoxide – A measurement of CO in an air sample or flue gas that takes into account the amount of excess air (oxygen, O2) in the sample, incorporating an adjustment to the as-measured CO ppm value, thus simulating air-free (oxygen-free) conditions in the sample. Usually measured in units of parts per million (ppm). See “As-Measured Carbon Monoxide”.

Ambient – Surrounding conditions. See “Inside Ambient”.

ANSI – American National Standards Institute.

ASHRAE – American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc.

As-Measured Carbon Monoxide – A measurement of CO in a sample of air or flue gas that does not take account of the amount of excess air (oxygen, O2) diluting the CO concentration. Usually measured in units of parts per million (ppm). See “Air-Free Carbon Monoxide”.

Atmospheric Burner – A burner utilizing atmospheric combustion. (Based on NFPA 54)

Atmospheric Combustion – Combustion which takes place under atmospheric pressure at a given altitude. (Based on NFPA 54)

Atmospheric Pressure – The weight of air and its contained water vapor on the surface of the earth. At sea level this pressure is 14.7 pounds per square inch. (Based on NFPA 54)

Balanced Flue Vent System – Term used for oil-fired systems to indicate a direct-vent appliance with positive pressure in the vent connector through which the gases of combustion pass.

Barometric Damper – See “Draft Regulator”.

Barometric Draft Regulator - See “Draft Regulator”.

Boiler – A space heating appliance that heats water with hot combustion gases.

Breeching or Breech – See “Vent Connector”.

Carbon Monoxide Emissions – Carbon monoxide (CO) is an odorless and colorless gas that can cause sickness and death. To measure the CO emissions in flue gas, the CO sample must be taken before dilution air enters the vent system. CO emissions are measured in parts per million (ppm). See “Air-Free Carbon Monoxide” and “As-Measured Carbon Monoxide”.

Category I Fan-Assisted Gas Appliance – An appliance that operates with negative static pressure in the vent, a temperature that is high enough to avoid condensation in vent, and an integral fan to draw a controlled amount of combustion supply air through the combustion chamber. Comment: Airtight vent connector is not required; induced combustion fan installed by manufacturer. (Based on NFPA 54)

Category I Gas Appliance – An appliance that operates with negative static pressure in the vent and a temperature that is high enough to avoid condensation in vent. Comment: May be atmospheric or fan-assisted combustion; airtight vent connector is not required. (Based on NFPA 54)

Category II Gas Appliance – An appliance that operates with negative static pressure in the vent and a temperature that is low enough to cause excessive condensation in the vent. Comment: No or very little equipment in this category. (Based on NFPA 54)

Category III Gas Appliance – An appliance that operates with positive static pressure in the vent and a temperature that is high enough to avoid condensation in vent. Comment: Airtight vent connector; vented through the wall; forced draft. (Based on NFPA 54) Caution: Check your program standards before drilling the vent connector of a Category III appliance for combustion safety testing.

Category IV Gas Appliance – An appliance that operates with positive static pressure in the vent and a temperature that is low enough to cause excessive condensation in the vent. Comment: Airtight vent connector; vented through the wall; forced draft; often referred to as a “90-plus” unit. (Based on NFPA 54) Caution: Check your program standards before drilling the vent connector of a Category IV appliance for combustion safety testing.

CAZ – See “Combustion Appliance Zone”.

Central Return – System of ducts or passages for distribution return air, which connect different areas of the house to a central location at the forced air furnace. (BPI HPA)

Chimney Flue – A passageway in a chimney for conveying combustion gases to the outdoors. (Based on NFPA 54)

Clean-Out Opening – An opening in a chimney (usually at its base) to allow inspection and the removal of ash or debris. (Based on NFPA 211).

Combustion Appliance Zone (CAZ) – Room and enclosed air volume that contains a combustion appliance. This may include, but is not limited to, a mechanical room, mechanical closet, or main body of the house.

Common Vent – The portion of the vent or chimney through which passes products of combustion from more than one appliance. (Based on NFPA 54)

Concentrically Constructed Direct-Vent – A direct-vent appliance that has an exhaust-gas vent and a combustion-supply-air vent arranged in a concentric fashion, i.e., one vent is inside the other with a space between the walls of each. Comment: Mobile home furnace vents are usually constructed this way; some Category I, direct-vent water heaters are constructed this way. Caution: Check your program standards and the manufacturer’s specifications before drilling the vent connector of a concentrically constructed direct-vent appliance for combustion safety testing.

Dilution Air – Air that enters a draft hood or draft regulator from the room in which the appliance is located. (Based on NFPA 54)

Direct-Vent Appliance – A combustion appliance for which all combustion gases are vented to the outdoors through an exhaust vent pipe and all combustion supply air is vented to the combustion chamber from the outdoors through a separate, dedicated supply-air vent. Comment: Most direct-vent gas appliances are Categories III and IV, but some are Category I; some direct-vent appliances utilize “Concentrically Constructed Direct-Vent”. (Based on NFPA 54)

Downdraft – Air flowing down a chimney or vent during the appliance off-cycle. (BPI HPA)

Draft – A pressure difference that causes combustion gases or air to move through a vent connector, flue, chimney, or combustion chamber. (Based on NFPA 54)

Draft Diverter – See “Draft Hood”.

Draft Fan – A mechanical fan used in a venting system to augment the natural draft in gas- and oil-fired appliances. These electrically operated, paddle-fan devices are installed in vent connectors. (NFPA 211)

Draft Hood – A nonadjustable device built into an appliance or a part of the vent connector that is intended to 1) provide for escape of flue gases if blockage or backdraft occurs, 2) prevent a downdraft of outdoor air from entering the appliance, 3) neutralize the effect of stack action of the chimney, and 4) lower the dew point temperature of the flue gas by the infusion of ambient room air. (Based on NFPA 54)

Draft Regulator – A self-regulating damper attached to a chimney or vent connector for the purpose of controlling draft. A draft regulator can reduce draft; it cannot increase draft.

Fan-Assisted Combustion – A combustion appliance with an integral fan to draw combustion supply air through the combustion chamber. Comment: Category I fan-assisted gas furnaces utilize this method of combustion control. (Based on NFPA 54)

Forced Draft – A vent system for which a fan installed at the combustion appliance moves combustion gases to the outdoors with positive static pressure in the vent pipe. Because of this positive pressure, the vent connector must be air-tight. Comment: Normally Category III or IV appliances; usually no draft diverter or barometric damper; fan for venting combustion gases at or near appliance; usually vented through the wall; may be condensing. (Based on NFPA 54) Caution: Check your program standards before drilling the vent connector of a forced draft appliance for combustion safety testing.  

Furnace – A space heating appliance that heats air with hot combustion gases.

Gas Oven Bake Burner – Oven burner used for baking located just below the oven compartment floor.

Gas Oven Broiler Burner – Oven burner used for broiling located at the top of the oven compartment.

Inches of Water Column (IWC) – A non-metric unit of pressure difference. One Pascal is equal to about 0.004 IWC.

Induced Combustion – See “Fan-Assisted Combustion”.

Induced Draft – A vent system for which a fan – installed at or very near the termination point of the vent pipe – moves the combustion gases to the outdoors with negative static pressure in the vent pipe. Comment: Normally Category I appliances; fan for venting combustion gases at point of exit to outdoors); vented through the wall. (Based on NFPA 54)

Inside Ambient – Air surrounding the equipment being tested within a dwelling. This does not include the air inside any part of the appliance or cabinet, or immediately outside any flue, vent pipe, or combustion gas outlet. (BPI HPA edited)

Isolated Outdoor Air Supply – Term used with oil-fired systems to indicate a vent pipe through which outdoor combustion supply is ducted to the oil burner. Comment: Often added on-site, these non-airtight outdoor air supply vents are sometimes installed with a vacuum relief damper that allows all the combustion supply air to be taken from the CAZ if the outdoor air inlet becomes blocked.

Mechanical Draft – A combustion appliance with induced draft of forced draft. (Based on NFPA 54)

Natural Draft – A vent system that relies on natural draft (buoyant air) to move combustion gases to the outdoors. Comment: Category I appliances; atmospheric, fan-assisted, or power burner type combustion; sometimes direct-vent; might be through-the-wall vented. (Based on NFPA 54)

Pascal (Pa) – The metric unit of pressure difference and is the equivalent to one Newton per square meter or one Joule per cubic meter. There are about 250 Pascals per IWC.

Power Burner – A burner for which air is supplied at a pressure greater than atmospheric pressure. Most oil-fired burners are power burners. Gas burners used to replace oil burners are usually power burners.

Power Draft – See “Mechanical Draft”.

Spillage – Combustion gases emerging from an appliance or venting system into the CAZ during burner operation.

Through-the-Wall Vented – Combustion appliances that are vented through a wall rather than into a vertical-rise chimney or vent. Such appliances are usually Category III or IV, but might also be Category I (e.g., direct-vent Category I water heater).

Vent Connector – The pipe that connects the combustion appliance to a vent or chimney. (Based on NFPA 54)

Venting System – A continuous passageway from a combustion appliance to the outdoors through which combustion gases can safely pass.
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