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  • #61
    Re: Tankless water heaters

    Originally posted by wrench spinner View Post
    From: http://ezinearticles.com/?Condensing...ers&id=4370344

    "As Tankless water heaters become more popular here so are increasing choices of types and manufactures.

    One term that is referred to lately is Condensing Tankless Water Heaters, so what is behind that?

    As the term applies tankless water heaters don't have a water storage tank like the traditional water heaters. The water in a tankless unit is heated as it flows through its heat exchanger which is heated through combustion, more intense that your regular water heater.

    In a typical combustion we burn the hydrogen content of the fuel and as the result hot gases are produced. One of these hot gases is steam or better water vapor. Now when these steam gases are cooled they turn into water that we generally refer to as condensation.

    The condensation water is acidic (pH 3-5) and hence corrosive. It will corrode steel metals and other materials.

    A Non-Condensing tankless water heater will push these hot gases through its vent to the outside. They will then cool down outside the unit. These gases have temperatures around 300 degrees F and must be vented through non-corrosive venting materials that can withstand the heat. Here is special stainless steel category 3 venting used, which is expensive.

    In the combustion process fuel was burned and that energy was used to heat the water, although not all of it. Because the hot exhausting gases contain heating energy that is not used to heat the water and are wasted by exhausting them to the open. The hotter the exhaust gases are the less energy is used in heating the water and hence lower efficiency.

    Non-condensing units have efficiencies around 80%, meaning around 20% of the heat is wasted and exhausted.

    Condensing Tankless Water Heaters

    Condensing Tankless Water Heaters extract the additional heat from the exhaust gases through various means and therefore exhaust cooler gases, usually around 100 degree F. As mentioned before cooling the exhaust gases produces condensation, in this case inside the unit. Since the exhaust gases are now much cooler a less expensive venting material can be used, mostly standard PVC schedule 40 is used as it can easily withstand the heat and the corrosively of the gases. Since we have captured the residual exhaust heat to heat the water we have achieved higher efficiency in the high 90% (up to 98%)."
    Nice article but it does not answer what I asked which is - in what way is the condensation from a tankless different to any other gas fired appliance. Do you have a reference in the gas code about it. You can reference the actual code as I have a copy of the 2011 code and handbook.

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    • #62
      Re: Tankless water heaters

      Originally posted by blue_can View Post
      Nice article but it does not answer what I asked which is - in what way is the condensation from a tankless different to any other gas fired appliance. Do you have a reference in the gas code about it. You can reference the actual code as I have a copy of the 2011 code and handbook.
      Some things receive approval, as NHMaster puts it "by the whores in charge", that are not directly addressed by the code....yet.

      Don't have it in front of me but it may have a note or exception for instantaneous appliances that "default to manufacturers instructions...."

      Code or instructions, whichever is more stringent (i.e. higher quality, hopefully) will apply.

      Quick answer, higher efficiency, potential for acidic condensation, install venting to withstand it.

      They put CATIII Stainless and manufacturers of such in the instructions for a reason.


      J.C.

      Comment


      • #63
        Re: Tankless water heaters

        because there isn't supposed to be condensation from a properly functioning older style boiler or water heater. the tankless cycles faster and the vent pipe generally doesn't get as hot leading to a cooling and settling of the exhaust in the vent that you wouldn't get from a traditional water heater.
        Last edited by wrench spinner; 02-14-2011, 11:23 AM. Reason: spelling

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        • #64
          Re: Tankless water heaters

          Originally posted by wrench spinner View Post
          because there isn't supposed to be condensation from a properly functioning older style boiler or water heater. the tankless cycles faster and the vent pipe generally doesn't get as hot leading to a cooling and settling of the exhaust in the vent that you wouldn't get from a traditional water heater.
          In theory yes , but horizontal vents are sloped to allow the moisture the drainback into the heater and be burnt so how much stays in the pipe is questionable.

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          • #65
            Re: Tankless water heaters

            Originally posted by blue_can View Post
            In theory yes , but horizontal vents are sloped to allow the moisture the drainback into the heater and be burnt so how much stays in the pipe is questionable.
            OK ill start with that, then even though it doesn't sit there don't you think that by continually dropping acid in the same area of pipe would lead to erosion? How long will it take? I don't know but for a couple hundred bucks why would you risk it?

            Comment


            • #66
              Re: Tankless water heaters

              I don't know the answer either but SS is not immune to corrosion. Possibly a better choice than galv but all things considered I did not consider it the level of danger you seemed to imply.

              Comment


              • #67
                Re: Tankless water heaters

                Another point about using the proper venting material.

                Tankless vent systems are under pressure from the fan within the heater. This is known as "Positive Pressure" venting and requires that the vent system be UL listed as positive pressure and sealed to prevent carbon monoxide from leaking out into the occupied space.

                Also if you do not have a vertical condensate tee installed at the top of the heater the slope of the pipe should be away from the heater. The manufactures do not want the condensate to enter back into the heater.
                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


                • #68
                  Re: Tankless water heaters

                  This is from Takagi's website. http://www.takagi.com/?p=installatio...php&page_id=66

                  Attached Files
                  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


                  • #69
                    Re: Tankless water heaters

                    He wants to know WHY Ron, he seems to understand it is required but he doesnt understand why.

                    Comment


                    • #70
                      Re: Tankless water heaters

                      That is all clearly galvanized pipe. How come? Cat III elbows are not marked with a 4

                      Comment


                      • #71
                        Re: Tankless water heaters

                        As it has been 8 years since I installed this I went back and consulted my 240FX install manual. This is what it says. I have underlined the relevant portions in red.

                        I'm pretty sure I read the manual carefully before installing. It only specifies sloping the vent upwards towards the exhaust and no mention of a condensate drain. So again I simply followed the manufacturer's instruction.

                        Ron - the whole point of sealing with either silicone or the welded seams is to prevent leakage due to the positive pressure. I initially sealed with silicone as per the manual but the inspector wanted to see it welded.

                        I assume you check all if your installs for minute leaks with a gas detector?
                        Attached Files
                        Last edited by blue_can; 02-14-2011, 05:13 PM.

                        Comment


                        • #72
                          Re: Tankless water heaters

                          Looks like you were doing what you were told by the instructions. No fault there.

                          The directions I find for the TK-1 no longer list galvanized for venting. Or I couldn't find it. Just that it had to be vented as prescribed by the National Fuel Code for a Category III Fuel Fired Appliance.

                          I would change it and just consider it maintenance. I know the vent is expensive.


                          J.C.

                          Comment


                          • #73
                            Re: Tankless water heaters

                            Originally posted by JCsPlumbing View Post
                            Looks like you were doing what you were told by the instructions. No fault there.

                            The directions I find for the TK-1 no longer list galvanized for venting. Or I couldn't find it. Just that it had to be vented as prescribed by the National Fuel Code for a Category III Fuel Fired Appliance.

                            I would change it and just consider it maintenance. I know the vent is expensive.


                            J.C.
                            Yes I agree JC. At the very least it will look nicer I will do it in the near future.

                            Comment


                            • #74
                              Re: Tankless water heaters

                              Originally posted by blue_can View Post
                              As it has been 8 years since I installed this I went back and consulted my 240FX install manual. This is what it says. I have underlined the relevant portions in red.

                              I'm pretty sure I read the manual carefully before installing. It only specifies sloping the vent upwards towards the exhaust and no mention of a condensate drain. So again I simply followed the manufacturer's instruction.

                              Ron - the whole point of sealing with either silicone or the welded seams is to prevent leakage due to the positive pressure. I initially sealed with silicone as per the manual but the inspector wanted to see it welded.

                              I assume you check all if your installs for minute leaks with a gas detector?
                              Bluecan

                              You are correct

                              Back in the late 90's, early 00's, Takagi was selling their TK1S unit to Bosch relabeled. Cat III pipe was just coming around as a replacement for Plexivent type products, and the tankless companies were not up to speed.

                              I can show you many installations working fine with galvanized on 82% tankless however, in your case the excessive cycling, vent and termination type and possibly the contaminants in your workshop has taken its toll on your venting. Fortunately its not tied to a sleeping area right?

                              Comment


                              • #75
                                Re: Tankless water heaters

                                I can' believe a Bosch tankless has made it 8 years...most don't live long enough to see their 5th birthday

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