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Combined venting

mferrer Member Posts: 32


  • mferrer
    mferrer Member Posts: 32
    Sorry guys- I mistakenly posted photos before asking the question. I have an AO Smith 40 gal gas fired hot water heater (3" flue) connected with a Frigidaire RA Series Gas Furnace (4" flue). They are connected to an aluminum liner in the chimney.

    The furnace was installed over 10 years ago like this. I recently installed the hot water heater. (2 yrs ago). I have recently read that it is not recommended to common vent a water heater with a power vented appliance. I believe my furnace has a small fan the vents exhaust and am concerned with the way this is piped out to the Chimney liner.

    I appreciate any helpful comments and/or suggestions. 

    Thank you!

  • Jamie Hall
    Jamie Hall Member Posts: 21,117
    Do they both have draught hoods? I see one on what I think is the water heater (insulation wrapped), although that is the larger of the two exhausts (you indicate that the water heater is the smaller).

    I can't see the other exhaust.

    Nor do I have the code answer for you -- but I can assure you that there is no way I'd connect a fan assisted (induced draught) appliance to the same flue that was connected to an appliance with a draught hood -- code or no code. What happens if the chimney gets blocked?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    EBEBRATT-Ed Member Posts: 13,456
    Which code are you under? NFPA 54 or International gas code?

    I need the BTUs of both appliances.

    The size of the liner

    The height from where the liner connects to the appliances to the top of the liner

    I am sure this can be done if sized properly

  • Ironman
    Ironman Member Posts: 7,119
    Look at the data plate on both appliances. Are they both listed as Category 1 appliances? If so, they can be common vented if the code AND manufacturer’s venting instructions are followed.

    If the furnace is a Category 1, then it’s “fan assisted”, not power vented.

    As Ed stated, there are chimney requirements that must be met.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • mferrer
    mferrer Member Posts: 32
    The height of the 5" liner is approximately 21ft. The BTU inputs are 74,000- Furnace and 40,000- HW Heater. Not sure of the code. I'm in central New Jersey.
    The nameplate says Category 1 on the Furnace. I have to remove the insulation to check the HW Heater.
    Thank you all!
    EBEBRATT-Ed Member Posts: 13,456

    Then they are both Cat 1 and can be vented together. Follow what @Ironman said. Download the instructions for bot and read the venting instructions. You need to know which code your on although there is probably little difference in venting
  • mferrer
    mferrer Member Posts: 32
    Thank you!
    Will do.
  • Bob Harper
    Bob Harper Member Posts: 977
    The vent connector to the WH should be increased to 4" because it has less than a 3 foot vent rise. See code sizing charts. That's why the mfr. included a 4" adapter onto the draft hood because it is so common and there isn't room for an increaser on many short rise installations.
    No foil tape on the connectors. Need 3 screws per joint equidistantly spaced. No screws or seams between 5-7 O'clock.
    5" liner probably ok if intact but it won't be for long. Aluminum liners can't take 80% furnaces for long even though legal at installation.
    Yes, you can common vent these two by code.
    No, you shouldn't. If the chimney becomes blocked, the furnace will happily vent out the draft hood without tripping the vacuum switch, high limit or flame rollout switches on the furnace. No spill switches on the WH draft hood. There is a way to modify this venting to make it reasonably acceptable. Take the NCI course.
    The insulation jacket on the WH needs to come off. Not needed and can come loose, which would block airflow into the combustion chamber, which would lead to CO production.
    The foam insulation on the water pipes needs to go. Not needed and encroaches into the 6" clearance to combustibles off the vent connector.
    The liner should extend into the room and have the listed mortar sleeve. The way the galvy wye is cemented into the wall can lead to hidden corrosion and failure unseen. Should be a ss liner swept into the room or with a tee at the base as a condensate trap or ss wye.