A-3 Gas Appliance and Building Air Requirements Introduction

The following terms will be used throughout this section. A complete list of terms for this section can be found in the Glossary.

• backdrafting: The reverse flow of gas in the flues of fuel-fired appliances that results in the intrusion of combustion by-products into the living space. (Section A-3.4)
• BTU (British Thermal Unit): A unit of energy used to measure the heat content of fuel. (Section A-3.2)
• complete combustion: The ideal burning process where there is enough oxygen to burn all the fuel completely, producing only carbon dioxide (CO₂), water vapor (H₂O), and heat as byproducts. (Section A-3.1)
• dilution air: Ambient air introduced into the venting system of natural draft appliances, used to control draft and cool vent gases. (Section A-3.2)
• excess air: Extra air supplied to the combustion process beyond the amount required for perfect combustion, typically 20-30% more than the theoretical amount needed for stoichiometric combustion. This ensures that all fuel is burned efficiently and completely. (Section A-3.1 and Section A-3.2)
• energy recovery ventilator (ERV): A ventilation system similar to HRV but also transfers moisture between the outgoing and incoming air streams to maintain balanced humidity levels in the building. (Section A-3.4)
• exfiltration: The leakage of room air out of the building. (Section A-3.4)
• flue gases: The gases produced as a result of combustion, including carbon dioxide (CO₂), water vapor (H₂O), and nitrogen (N₂). (Section A-3.2)
• gas flow rate: The amount of gas flowing through an appliance, typically measured in cubic feet per hour (CFH), and used to calculate air supply requirements. (Section A-3.2)
• heat recovery ventilator: A system that recovers heat from outgoing exhaust air and transfers it to incoming fresh air, helping to improve energy efficiency and indoor air quality. (Figure 5, Section A-3.4)
• incomplete combustion: Occurs when there is insufficient oxygen for the fuel to burn completely, producing hazardous byproducts like carbon monoxide (CO), soot, and aldehydes. (Section A-3.1)
• induced-draft burner: A type of power burner where the fan or blower is located downstream of the combustion zone, creating draft by drawing gases out of the combustion chamber. (Section A-3.3)
• infiltration: The unintentional introduction of outside air into a building; also referred to as air leakage. (Section A-3.4)
• power burner: A burner with mechanical draft that generates sufficient pressure to overcome resistance in the combustion chamber, appliance, and venting system. (Section A-3.3)
• power venter: A mechanical draft system used to assist venting in natural draft appliances, often used to overcome venting challenges like excessive negative pressure. (Section A-3.3)
• primary air: The portion of combustion air mixed with the fuel gas before ignition, typically one-third of the total combustion air. (Figure 2, Section A-3.2)
• radon mitigation: Methods used to reduce the presence of radon gas in a building, such as installing a subfloor depressurization system to create a pressure difference that prevents radon from entering the building. (Section A-3.4)
• secondary air: The additional air required to complete the combustion process, typically two-thirds of the total combustion air. (Section A-3.2)
• soil gas: A mixture of air, water vapour, and pollutants, such as radon, that enters a building through below-grade leaks in the building envelope, potentially affecting indoor air quality. (Section A-3.4)
• stack effect (chimney effect): The phenomenon where hot air rises due to its lower density, creating a natural flow of air into and out of buildings, chimneys, and vents. (Section A-3.3)
• ventilation: The intentional introduction of outdoor air into a space to control indoor air quality by diluting and displacing indoor pollutants; can also be used for purposes of thermal comfort or dehumidification. (Section A-3.4)