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  1. #1
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    Default Multiple Appliance Venting Systems

    Hey guys, I'm a chimney tech and I ran across a code in the IRC 2006 that I need some clarification on.

    -----

    "M1801.11 Multiple-appliance venting systems: Two or more listed and labeled appliances connected to a common natural draft venting system shall comply with the following requirements:

    1)
    2)
    3) Connectors serving appliances operating under a natural draft shall not be connected to any portion of a mechanical draft system operating under positive pressure."

    Does this mean that you cannot connect a water heater and a furnace together with a Y-Pipe before it goes into a chimney?

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  2. #2
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    Mar 2007
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    Default Re: Multiple Appliance Venting Systems

    Quote Originally Posted by Justin Fehl View Post
    Hey guys, I'm a chimney tech and I ran across a code in the IRC 2006 that I need some clarification on.

    -----

    "M1801.11 Multiple-appliance venting systems: Two or more listed and labeled appliances connected to a common natural draft venting system shall comply with the following requirements:

    1)
    2)
    3) Connectors serving appliances operating under a natural draft shall not be connected to any portion of a mechanical draft system operating under positive pressure."

    Does this mean that you cannot connect a water heater and a furnace together with a Y-Pipe before it goes into a chimney?
    There are different gas appliance categories, I through IV, and positive pressure such as high efficiency furnaces with PVC pipe vents function under positive pressure where as standard water heaters with single wall or b-vent metal chimneys and draft hoods function under negative pressure. The negative pressure means the chimney stacks draw or draft sucking exhaust to outdoors rather than being pushed with fans to outside. Be careful though, inducer fans are used on some furnaces that are actually negative pressure systems.

    "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. See Figure 1. (Based on NFPA 54)
    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. See Figure 2 (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)
    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􏰂or 􏰁condensing􏰂 unit.See Figure 3. (Based on NFPA 54)"




    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  3. #3
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    Default Re: Multiple Appliance Venting Systems

    Quote Originally Posted by Jim Luttrall View Post
    There are different gas appliance categories, I through IV, and positive pressure such as high efficiency furnaces with PVC pipe vents function under positive pressure where as standard water heaters with single wall or b-vent metal chimneys and draft hoods function under negative pressure. The negative pressure means the chimney stacks draw or draft sucking exhaust to outdoors rather than being pushed with fans to outside. Be careful though, inducer fans are used on some furnaces that are actually negative pressure systems.

    "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. See Figure 1. (Based on NFPA 54)
    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. See Figure 2 (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)
    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-plusor condensingunit.See Figure 3. (Based on NFPA 54)"


    Jim, thank you for the helpful response. The situations I am normally installing are a natural draft gas water heater and a forced hot air gas furnace. I combine them into a y-pipe outside of the wall before going into the chimney where they connect to a stainless steel liner. See pic below. The chimney stack is under negative pressure. But does the forced hot air from the furnace put it in positive?

    phpSaJUMGAM.jpg


  4. #4
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    Default Re: Multiple Appliance Venting Systems

    Quote Originally Posted by Justin Fehl View Post
    Jim, thank you for the helpful response. The situations I am normally installing are a natural draft gas water heater and a forced hot air gas furnace. I combine them into a y-pipe outside of the wall before going into the chimney where they connect to a stainless steel liner. See pic below. The chimney stack is under negative pressure. But does the forced hot air from the furnace put it in positive?

    phpSaJUMGAM.jpg
    In general, if it has a draft hood it is not a positive pressure vent. Just because the unit has a draft inducer motor does not put the entire vent system under positive pressure. You need to look at each unit individually and follow the manufacturers installation requirements for that unit.

    Jim Luttrall
    www.MrInspector.net
    Plano, Texas

  5. #5
    Join Date
    Oct 2010
    Location
    Luxemburg, Wisconsin
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    Default Re: Multiple Appliance Venting Systems

    Quote Originally Posted by Jim Luttrall View Post
    In general, if it has a draft hood it is not a positive pressure vent. Just because the unit has a draft inducer motor does not put the entire vent system under positive pressure. You need to look at each unit individually and follow the manufacturers installation requirements for that unit.
    In the photo it appears that both the boiler and the water heater are natural draft (the boiler has a draft hood).


  6. #6
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    Mar 2010
    Location
    conyers, ga
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    79

    Default Re: Multiple Appliance Venting Systems

    Quote Originally Posted by Jim Luttrall View Post
    In general, if it has a draft hood it is not a positive pressure vent. Just because the unit has a draft inducer motor does not put the entire vent system under positive pressure. You need to look at each unit individually and follow the manufacturers installation requirements for that unit.
    I had thought correct if wrong, that could be old terminology in the description of furnaces meaning that the heated air is forced through the supply ducts rather than the much older drafted air systems log ago, so not implying the nature of the gas exhaust ?


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