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Gas and oil shared flues

alby42 Member Posts: 9
Any ideas whether or not sharing a single flue is practicle or accepted with tow types of exhaust? Oil fired warm air heater and a gas fired hot water heater on a shared vent pipe - as shown in photo's.. I believe the liner in the house top chimney extends to the appliances but is not directly attached..


  • Bob Harper
    Bob Harper Member Posts: 914

    The codes allow inerconnection if the common vent capacity is enough for both appliances simultaneously,  have primary safety controls and it works.

    Now, this does not guarantee performance. In the case illustrated, if the chimney became blocked either appliance could easily vent out the relief on the other without tripping any safeties.

    The chimney should get a Level II inspection to determine suitability first. If the liner is incomplete or damaged, it must be relined full length. The two appliances can then be manifolded together with spill switches on the draft hood of the WH and barometric damper. That 3" vent connector on the WH is undersized and improperly supported. The manifold is over-crimped where it enters the breaching. I don't see a cleanout. Once all repaired, conduct combustion analysis with a draft interference test to ensure proper function.


  • alby42
    alby42 Member Posts: 9
    big thanks

    I am happy with your thoughts A+
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