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2 Existing hydrotherm to 1 Superhot AAA840 (Venting) (Canadian Code)

Spartanator Member Posts: 3
edited November 2020 in Gas Heating
Hey everybody,

We have a couple of apartment buildings that we are going to be doing some retrofit work to. We're going to be installing 1 Superhot AAA-840 Boiler (1 - 14" Flue Collar) in lieu of 2 Hydrotherm Boilers (4 - 8" Flue Collars).

My biggest worry is my combustion vent sizing. I've determined that the existing Chimney will be able to handle the capacity load wise, but my worry is in wondering if I can downsize our new 14" flue collar to 10". (I know by the looks of things it meets NFPA 54 code, but please correct me if I'm wrong.)

We will be running APPROX 25'-30' Height, with a lateral of ~5'.

I would love a hand with some information, and I'd love to be able to understand my codes better without having to call the authority having jurisdiction.

Kindest Regards!


  • Zman
    Zman Member Posts: 7,009
    I would kick this to the manufacture. Draw up what you have in mind and ask them to bless it.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Spartanator
    Spartanator Member Posts: 3
    Zman said:
    I would kick this to the manufacture. Draw up what you have in mind and ask them to bless it.

    So, I did end up Calling Allied engineering for more advice, and to see if they've run into this situation before. 

    In our GVR (General Venting Requirements)   There is basically an Excerpt from the NFPA 54 stating 12" and over we can decrease 2 Sizes (14" to 10")  as long as our vent maintains a minimum of 10' in height. 

    I wanted to come back and deliver that in case anyone gets stumped, and has a massive brain fart like I did.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 2,421
    You might want to run that by the AHJ. Give them all the info you have regarding the vent connector size you are planning on using. Also mention that based on your calculations you believe there will be other issues relating to oversizing the vent connector that will be addressed by your proposed design. You will find that asking for their input before they have a question at the time of a final inspection, will go a long way in gaining a smooth approval process. (in most cases, if you make them feel important and smart)
    Edward Young
    Retired HVAC Contractor from So. Jersey Shore.
    Cleaned & services first oil heating system at age 16