Adding or Removing Gas Appliances from Chimneys and Vents

Appliances Governed by these Code Provisions
Apply these code provisions to chimneys and vents used by gas-burning appliances. Note that similar provisions for solid and liquid fuel-burning appliances exist in IRC Chapter 18. Description of Potential Problems when Adding or Removing Fuel-Burning Appliances Every fuel-burning appliance has different characteristics that will affect the operation of a chimney or vent. These characteristics include the quantity of flue gasses from the appliance, the temperature of the flue gasses, and the amount of water vapor in the flue gasses. Adding or removing appliances may cause a chimney or vent that once operated satisfactorily to operate improperly. Problems that may occur include backdrafting of exhaust gasses into the home and condensation of moisture that can quickly damage the chimney or vent. Backdrafting and damaged chimneys and vents are a significant safety hazard.

Recalculate Chimney or Vent Size when Adding Gas Appliances
1. Recalculate the size of a chimney or a vent when adding or removing a gas appliance. The new chimney or vent size could increase, decrease, or remain the same depending on the type and efficiency of the appliance added or removed. Account for the new size requirements based on all gas appliances connected to the chimney or vent. To calculate the size of a gas appliance vent, use Section G2428.
2. Do not vent solid-fuel-burning appliances (such as a wood-burning fireplace) and appliances using other fuels (such as a gas furnace) into the same flue. Provide each solid-fuel-burning appliance with its own separate flue.

Cleaning and Inspection of Chimneys and Vents
1. Inspect chimney flues and vents when adding or removing gas appliances. Ensure that the flue is continuous and free of cracks, damage, or deterioration that could allow escape of combustion products. Ensure required clearances to combustible materials and ensure that required firestops are installed.
2. Clean flues that have been used for liquid or solid-fueled appliances before inspecting the flue.

Chimney Cleanout Openings
1. Install in chimneys a cleanout opening that has a tight-fitting, noncombustible door with an opening height of at least (≥) 6 inches. Locate the upper edge of the door at least (≥) 6 inches below the lowest chimney inlet opening.