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Venting a Tankless Water Heater

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  • Venting a Tankless Water Heater

    Hello,

    In '05 I had a new furnace put in (Comfortmaker C8MPV075 - 80% AFUE) that required a chimney liner to be installed. My furnace and current tank water heater vents into this chimney liner.

    I am currently looking at a Rheem Tankless water heater and wanted to find out if I would be able to vent into this same liner. I don't know the specs on the liner that was put in and am not sure how to find that out. If the liner meets the requirements of the furnace would it also meet the requirements for a tankless water heater. Rheem notes a required 3"/5" UL approved category 3 stainless steel vent.

    Thanks,
    Chuck
    Help me make Wishes Come True!
    Support the Make-A-Wish Foundation

  • #2
    Re: Venting a Tankless Water Heater

    Is your current liner made of stainless steel? Stainless exhaust is specified for one of 2 reasons...

    1. Exhaust temp is so high that it will cook galv. steel pipe. (this is not the case here though...)

    2. To squeeze every BTU out of the fuel supply (to raise the product efficiency) the exhaust temp is so low ( below 212 degrees) that the exhaust condenses thus making it not capable of carrying the byproducts of combustion
    out the stack... These by-products are acidic and condense to the side wall of the exhaust causing corrosion thus the need for stainless steel.
    If you liner is made of metal and not stainless a condensing exhaust is not a good idea...

    Which model of Rheem are you installing, Single pipe or 2 pipe...

    If single pipe where are you planning on getting your combustion air from?

    Your current furnace being 80% has a non condensing exhaust (above 212 degrees) and will not have these issues.

    A mechanical engineer should know these things
    Last edited by OkieBill; 06-14-2009, 12:50 PM.

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    • #3
      Re: Venting a Tankless Water Heater

      I was digging around for the furnace installation instructions and found that the liner installed is Aluminum.

      I am looking at a single unit residential 66 series water heater. I am not exactly sure what is meant by single or double pipe or what else would be required for install.
      Help me make Wishes Come True!
      Support the Make-A-Wish Foundation

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      • #4
        Re: Venting a Tankless Water Heater

        Originally posted by cory7 View Post
        I was digging around for the furnace installation instructions and found that the liner installed is Aluminum.

        I am looking at a single unit residential 66 series water heater. I am not exactly sure what is meant by single or double pipe or what else would be required for install.
        A qualified plumber

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        • #5
          Re: Venting a Tankless Water Heater

          Originally posted by plumberscrack View Post
          A qualified plumber
          To clarify, most Tankless manufactures require a licensed plumber and even a certified installer (plumber that took the installing class for their units) to keep the warranty valid.
          Ron Hasil Lic #058-160417
          Ron's Facebook
          A-Archer Sewer & Plumbing specializing in:
          Tankless Water Heaters | Drain and Sewer Cleaning
          Sump and Ejector Pumps | Backflow RPZ Testing

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          • #6
            Re: Venting a Tankless Water Heater

            Originally posted by plumberscrack View Post
            A qualified plumber
            It sure does, I just like to understand everything involved so that I can ask the right questions and not be taken.

            Chuck
            Help me make Wishes Come True!
            Support the Make-A-Wish Foundation

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            • #7
              Re: Venting a Tankless Water Heater

              I like the units that allow for PVC venting like the Noritz 841
              Last edited by SewerRatz; 08-01-2009, 09:11 AM.
              Ron Hasil Lic #058-160417
              Ron's Facebook
              A-Archer Sewer & Plumbing specializing in:
              Tankless Water Heaters | Drain and Sewer Cleaning
              Sump and Ejector Pumps | Backflow RPZ Testing

              Comment


              • #8
                Re: Venting a Tankless Water Heater

                A pvc ventable unit would solve your current stack temp / liner material issues...

                I would stay away from Naiven IMO they are having some problems with their current generation units.

                Single pipe / Concentric vent ( Combustion Air and Vent through a single double wall pipe) or 2 pipe (Combustion Air and Vent each with it's own pipe)

                I have zero experience with Rheem Tankless, Isn't that the Home Depot House brand?

                FYI this is not a DIY as Crack and SewerRatz have stated.


                Okie

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                • #9
                  Re: Venting a Tankless Water Heater

                  Originally posted by OkieBill View Post
                  A pvc ventable unit would solve your current stack temp / liner material issues...

                  I would stay away from Naiven IMO they are having some problems with their current generation units.

                  Single pipe / Concentric vent ( Combustion Air and Vent through a single double wall pipe) or 2 pipe (Combustion Air and Vent each with it's own pipe)

                  I have zero experience with Rheem Tankless, Isn't that the Home Depot House brand?

                  FYI this is not a DIY as Crack and SewerRatz have stated.


                  Okie
                  Small experience with Rheem. Not the HD brand, at least in my area. It's part of the Paloma group.

                  J.C.

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                  • #10
                    Re: Venting a Tankless Water Heater

                    Tankless water heaters, both Cat III (stainless steel) and PVC must be vented separately. That I'm aware of, you can't even combine the vents of two tankless heaters.

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                    • #11
                      Re: Venting a Tankless Water Heater

                      I would look in to solar you dont have to pay for the sun and if you use Drain-Water Heat Recovery system you can recycle that same energy.http://www.energysavers.gov/your_hom.../mytopic=13040rgy

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                      • #12
                        Re: Venting a Tankless Water Heater

                        I appreciate everyone’s feedback!
                        Help me make Wishes Come True!
                        Support the Make-A-Wish Foundation

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                        • #13
                          Re: Venting a Tankless Water Heater

                          I have not heard a lot of good things about Rheem tankless. It could be one of those things though that you always hear someone complain, but never compliment too ... Google is your friend. Rinnai and Takagi (not in any particular order) are usually the bigger names in tankless. Noritz too.

                          When I purchased my tankless, prior to selecting the installer, I had the installer give me references. That gave me good local feedback on how the tankless might perform in my area and what people thought of the specific model I was interested in.

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                          • #14
                            Re: Venting a Tankless Water Heater

                            Originally posted by Clipper City Plumber View Post
                            I would look in to solar you dont have to pay for the sun and if you use Drain-Water Heat Recovery system you can recycle that same energy.http://www.energysavers.gov/your_hom.../mytopic=13040rgy


                            I have taken out 3 or 4 solar water heaters in the last year have a bid in for another. The expense to maintain them is apparently too high. Customers are just replacing them with regular tanks.

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