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  • Tankless temperature question

    One of my customers bought a new/used house. The house has a new Poloma, Model PTG-74PVN-1 tankless water heater. The customer would like to raise the temperature beyond 120 degrees which seems to be the maximum, according to the small control panel.

    Since the heater is new it is guaranteed, and he will call the plumber who installed it for information tomorrow. But I wondered is 120 degrees considered a maximum for these tankless heaters or is his messed up?

    From reading these plumbing threads I told him I thought the heater needed to be flushed every year and to be sure to talk to the plumber about it. He gave me a sigh.

    Later, as he was showing me through the house, we ended up in the upstairs bathroom. He showed me how he turns on the tub and waits for the hot water then he told me how he can't regulate the water temperature by turning the faucet more. The guy actually thought that opening the faucet more increased the water temperature. When I explained that opening the faucet only increased volume he was dumbfounded. I explained a few more times and he finally got it. Cheese Louise, that is pretty basic stuff for a home owner, or a fifth grader, or at least should be.

    Maybe for guys like him 100 degrees should be max.

    Thanks,
    -Tom

  • #2
    Re: Tankless temperature question

    Yes this is the factory default on this heater. The default can be overriden to increase temp. output. The plumber should know what to do.

    J.C.

    Comment


    • #3
      Re: Tankless temperature question

      Why would he want to increase the temperature? 120 F is already scalding for some and will just increase his energy bills and mean mixing more cold water with it to cool it down anyways.

      Comment


      • #4
        Re: Tankless temperature question

        That's assuming the temp is 120 at the tap. And tankless are controlled by volume demand vs. temp. rise going through them. By increasing the temp. output you can push the unit to it's highest output giving you more usable volume.

        Example: Default setting you can run maybe a shower and a faucet simultaneously.

        High setting you can maybe run 2 showers and a faucet simultaneously.

        Check with others though. I'm the dumb guy.

        J.C.

        Comment


        • #5
          Re: Tankless temperature question

          But aren't the units good for such and such a temperature rise for a given volume? Will you neccessarily get more volume/hot water with a higher temperature as you would then tend to use less to mix? I would think it would almost be proportional as far as volume versus temperature as you climbed higher which would negate the difference (assuming I'm right). Also, the higher temps put more stress on your piping system, fixtures, valves, etc. Maybe not a lot in the grand scheme of things but over time it adds up.

          Comment


          • #6
            Re: Tankless temperature question

            No.

            J.C.

            Comment


            • #7
              Re: Tankless temperature question

              Thank you for the information. I called my customer this morning and explained how two showers can probably be run simultaneously if the temp setting is raised. I have been talking with the husband of this couple but this morning I talked with the wife. She told me she thought the water was hot enough. Sheesh, don't couples discuss issues any more. Anyway they will call the plumber and ask his opinion of raising the temp setting.

              Thank you again for the help.

              -Tom

              Comment


              • #8
                Re: Tankless temperature question

                There is a good calculator here, then click on "Flow VS Ignition". It is obviously Rinnai based, but I would think the principles are the same. You will notice as you increase the "Remote Temperature", default is 120, that less hot water is required from the unit. Which makes sense, but you are also wasting energy because with higher settings it typically would mean you would have to cool the water more to a usable temperature, thus wasting the energy that you just spent getting it to 130/140/whatever. However, with that being said, I have heard that this is a common trick for tankless owners to get an extra appliance out of the unit. Thus far with my cold incoming water temperature, I have not had a need to up it.

                My Rinnai has a max of 140. With another controller, I can get it to go to 180, but that also changes the terms of my warranty (12 down to 5 I think). There may be another controller option for the Paloma if the max is only 120. It may also change the warranty terms of the unit too.
                Last edited by theoak; 09-22-2008, 09:46 AM.

                Comment


                • #9
                  Re: Tankless temperature question

                  Originally posted by theoak View Post
                  but you are also wasting energy because with higher settings it typically would mean you would have to cool the water more to a usable temperature, thus wasting the energy that you just spent getting it to 130/140/whatever.
                  That I don't get. If you input the same amount of heat into a smaller volume of water (thus making it have a higher temperature), why would that waste more energy. You'll have a higher ratio of cold water, but the total BTU expenditure should be pretty much the same.

                  What am I missing here?

                  Comment


                  • #10
                    Re: Tankless temperature question

                    Of course most plumbing codes prohibit water temperatures in excess of 120 degrees. So if you crank it up you need to temper it back down at the faucets lest some innocent child be scalded.
                    sigpic

                    Comment


                    • #11
                      Re: Tankless temperature question

                      Originally posted by cpw View Post
                      That I don't get. If you input the same amount of heat into a smaller volume of water (thus making it have a higher temperature), why would that waste more energy. You'll have a higher ratio of cold water, but the total BTU expenditure should be pretty much the same.

                      What am I missing here?
                      You know, that is a really good point. The calculator link I provided even demonstrates that. If you change the "Remote Temperature" the BTU value does not change. If you change other settings, then the BTU value does change.

                      Comment


                      • #12
                        Re: Tankless temperature question

                        sounds really complicated all of a sudden.

                        -i'm going to be the cold water.

                        -the sexy dirty person(s) wants to take a shower.

                        -she,(trust me on this one guys) turns on the left side of the faucet. i start my journey to wonderland.

                        #1-i travel the "domestic cold water supply" highway until i take the off-ramp to get to "tankless'" place.

                        #2-i go visit my buddy, tankless. he shares a duplex with "hot water heating system". i receive a warm welcome and an even warmer departure. good guy that tankless. (i can only be as warm/hot as the temp. in the boiler)

                        #3-so next i'm cruising along "really hotwater pipe" road and i pass by the cop, "T&P valve". don't p*ss that dude off. I hear that if he gets 210 degrees f, or 150 psi, yu justed p*ssed him off. don't go there.

                        #4-so i'm traveling along really hot pipe road, still feeling pretty hot, and i run into one of my cousins. "cold mixing water" at "mixing valve" junction. he says to me, "howz it goin eh? i say "really goot, eh. he says to me, "hey, according to this junction, your too hot, so i came to cool you down eh." I say, "okay,....eh."

                        #5-after leaving mixing valve junction, me and my cousin turned onto "mixed hotwater" street. i drove at the legal limit of 120 degrees f maximum.

                        #6-we finally get to shower's place. at the door, we run into our other cousin, "straight cold water". so we all visit together. remember the sexy dirty person? wonderland.

                        if the customer requests hotter water, it is my opinion that they are solely responsible for turning up the hw temp. i won't go above factory settings (120f). i will however teach the homeowner (not tenent) how to increase the hw temp safely, and at the same time explain the inheirent dangers of doing so.

                        -reduce the flow of cold mixing water increases the mixed hw temp.

                        -the mixed hw temp. can only get to the max temp of the boiler it getting heat from. even if the cw inlet to the mixing valve is completely shut-off.

                        -hotter water = higher btu consumption=more fuel=more $$

                        i'm not aware of a self-modulating mixing valve. i'm so out of touch with modern technology i might as well be living at the north pole.

                        i have to keep reminding myself that not everyboby is a plumber and not everybody is as smart as we are.

                        when it comes right down to it, it all boils down to a comfortable place to poo.

                        Comment


                        • #13
                          Re: Tankless temperature question

                          OUT! OUT of the Ask the Plumbing Experts you two! And you can run me away from the cpu forum when I start spouting off about harddrives!

                          J.C.

                          Comment


                          • #14
                            Re: Tankless temperature question

                            Originally posted by JCsPlumbing View Post
                            OUT! OUT of the Ask the Plumbing Experts you two!
                            I'm not sure if I am supposed to be taking you seriously here or not.

                            Comment


                            • #15
                              Re: Tankless temperature question

                              Originally posted by cpw View Post
                              I'm not sure if I am supposed to be taking you seriously here or not.
                              You know not to take me to seriously C.

                              But maybe the other guy should.

                              J.C.

                              Comment

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