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Thread: CSST Clearance

  1. #1
    Join Date
    Sep 2007
    Fredericksburg, VA

    Default CSST Clearance

    End-of-builder's warranty inspection yesterday. Yellow clad CSST was used as the primary natural gas supply line(s) throughout the house. The builder used black steel for sediment connections and fixed appliance connections. There is a furnace/water heater room in the basement. The furnace is a gas with a fan assisted vent exhaust. The water heater is a 74 Gal unit with a standard draft hood exhaust. Both the furnace and WH use a single wall corrugated metal connector vent pipe that connects to a B-vent stack up to through the house and roof. The question deals with the clearance from the corrugated vent connectors to the gas supply line and a NM electric wire that are run to the furnace. The attached photos indicate that the gas line and wire are only about 1.5 to 2" inches aways from the wall of the CVP. Would the Yellow cladding of the CSST and plastic insulation of the NM wire be considered "Combustible" material under IRC 2006?

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    The above statements are expressed solely as my opinion and in all probability will conflict with someone else's.
    Stu, Fredericksburg VA

  2. #2
    Join Date
    Feb 2008
    Sioux City, Iowa

    Default Re: CSST Clearance

    I am not sure about the items being listed as combustable but is that aluminum vent stack? In my area, aluminum is not allowed on the vet pipes from the furnace and/or water heater.

  3. #3
    Jon Randolph's Avatar
    Jon Randolph Guest

    Default Re: CSST Clearance

    Quote Originally Posted by Mike Tracy View Post
    I am not sure about the items being listed as combustable but is that aluminum vent stack? In my area, aluminum is not allowed on the vet pipes from the furnace and/or water heater.
    Corrugated stainless steel, most likely.

    I would treat the corrugated vent as a single wall vent and say that it has to be at least 6" from combustibles including the romex and CCST jacket and the refrigerant line insulation in the backgound.

  4. #4
    David Banks's Avatar
    David Banks Guest

    Default Re: CSST Clearance

    I checked Gastite Install manual and this is not addressed. Only thing I found was this. Look at Part-3 H. May apply. Do not know. Hopefully Bob Harper will chime in.

  5. #5
    Join Date
    Mar 2007
    Near Philly, Pa.

    Cool Re: CSST Clearance

    There are two issues here:
    1 flexible vent connector
    2 is the plastic coating rated "combustible"

    To answer 2, yes. When dealing with clearances to venting equipment, the definition of "combustible" per NFPA 211 would mean anything that won't burst into flames, crumble or lose half its mass after a 1,342F vertical tube furnace test (ASTM E-136) I think its safe to say that polyester jacket would decompose before those temps were reached.

    As for 1, if it is an unlisted flexible vent connector for gas only then it carries a 6 inch clearance to combustibles. However, unlisted flex can only be used if it meets the requirements set forth in the IRC or are accepted by the AHJ AND are upsized for flow capacity. You must derate flex 20% plus another 20% if it has turns. If this is stainless flex, it would probably be acceptable to the AHJ whereas unlisted aluminum flex should not. There are some stainless liners that easily separate seams and are not durable enough for being exposed as a vent connector yet somehow still pass UL1777.

    Now, if this is a listed vent connector, then you go by the listed clearance, which is usually 1".

    Keep the fire in the fireplace.


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