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  • Helping Someone....

    A retired friend/contractor wants me to look into the pipe he needs to tack up PEX for radiant flooring.

    Has to penetrate subfloor and prefinished (thinner) hardwood.

    Wants to use existing water heater. Gas. Probably 40,000 btu. I know, I know, I know. But for some reason I run into stories here where people do this with there lower btu heater and always seem happy.

    His forced air serviceman states that two of his guys have done it and are very happy.

    Anyway, he wants to explore it himself and has asked me about materials.

    I told him to use O2 PEX.
    Diffuser plates? I wasn't sure. Get conflicting information as to whether they are worth the trouble or not.
    Circulating pump. (Grundfos? Taco?)
    Thermostatic valve to get the domestic temp down.

    He wants to staple it up under the subfloor then put the insulation back underneath.

    Heat is above in attic with ceiling vents. Cold all the time according to him.

    Anyway. Ideas? Problems?

    Thanks.

    Back to work.


    J.C.

  • #2
    Re: Helping Someone....

    A proper heat loss/radiant design with flooring materials inputed will result in giving you tube size required, GPM flow rate needed, tube spacing, operating water temp needed, and actual floor temps, at a selected outdoor design temperature.

    Sometimes plates are absolutely needed, but they always allow for a lower water temp, sometimes smaller tubing and will offer more comfort, since heat is spread out evenly.

    Gas water heaters make lousy boilers since they are so inefficient, not to mention your limited to about 25,000 net BTU's at their 65% operating efficiency. Given your in the north, thats only about 850 square ft house.

    Also if he plans on using the tank as dual purpose, not only is it dangerous because of bacteria growing in stagnant water left in tube when not heating and eventually you drink, bathe and inhale in shower, there may no longer be enough hot water when trying to do both. Systems like this must be built with non ferrous metal components adding to the cost.

    Otherwise it looks like this:
    Attached Files

    Comment


    • #3
      Re: Helping Someone....

      Supplemental heat along with forced air? Maybe.
      You could use a plate exchanger off your heater to isolate circuits form domestic.

      Comment


      • #4
        Re: Helping Someone....

        Originally posted by spoon View Post
        Supplemental heat along with forced air? Maybe.
        You could use a plate exchanger off your heater to isolate circuits form domestic.
        He just called. Yes, supplemental heat along with the forced air. He estimates that the rooms he would like to do this in equal out to around 500 square feet.

        Thanks.


        J.C.

        Comment


        • #5
          Re: Helping Someone....

          getting the system designed will offer the best results.

          But that's not really what he's asking for.

          300 foot rolls of half inch pex. O2 barrier isn't required since you're running it to a potable component. plates will give better results with higher upfront cost. when he reinsulates make sure he leaves an air gap between the top of the insulation and the bottom of the subfloor. if you're not using plates don't tack the tubing straight to the subloor, go about an inch below it.
          No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

          Comment


          • #6
            Re: Helping Someone....

            Originally posted by MoJourneyman View Post
            getting the system designed will offer the best results.

            But that's not really what he's asking for.

            300 foot rolls of half inch pex. O2 barrier isn't required since you're running it to a potable component. plates will give better results with higher upfront cost. when he reinsulates make sure he leaves an air gap between the top of the insulation and the bottom of the subfloor. if you're not using plates don't tack the tubing straight to the subloor, go about an inch below it.
            Thanks. Very helpful.

            Should there be zones? I told him I was talking out of my rear but was thinking that once you started pushing 200' to 300' that the temp was going to drop and the heat removed from the water. So it better be getting back to the heater.

            Right? Wrong?

            Any recommendations on thermostats & zone controls if needed?

            I just got off the phone with another guy I know. Licensed HVAC installer. I described what we're talking about and he was like.....huh?

            That's what I run into more times than not here in relation to HVAC.


            Thanks again.


            J.C.

            Comment


            • #7
              Re: Helping Someone....

              only reason to do seperate zones in this scenario is if he has rooms he wants at different temps. easiest way is just one zone, if he's looking at 800 square feet, figure 1600 feet of pipe, but that isn't divisible by 300, so figure 1800 feet of pipe.


              and before the vultures start mauling me, this is an un-engineered system to give the guy warm floors. he's wanting to do an 80k btu job on 40k btus. it's supplemental at best. but we understood that at the start of this thread.

              I use something similar to this for the control, 120 for the pump gets wired into it, so does the t-stat wire. any thermostat you like will work, just needs 2 wires.

              i'd install a circuit setter somewhere nearish to the pump so you can get your delta t down into the right range.
              No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

              Comment


              • #8
                Re: Helping Someone....

                also, one zone, but multiple loops on that zone, 300 is about the furthest you'd want to push 1/2 pipe, so 6 300 foot rolls of pipe off of a manifold.
                No, it's not rocket science, it's plumbing and unlike rocket science it requires a license.

                Comment


                • #9
                  Re: Helping Someone....

                  Thanks. Helps alot with the homework.


                  J.C.

                  Comment


                  • #10
                    Re: Helping Someone....

                    Now I'm thinking again. Danger alert.

                    BTU's. A BTU is a BTU. Right?

                    So would it be a quick conclusion to azz-u-me that one needed an equal BTU water heater or boiler to achieve the same heating ability as a forced air systems BTU's?


                    J.C.

                    Comment


                    • #11
                      Re: Helping Someone....

                      I'm a big fan of zoned heating.

                      Comment


                      • #12
                        Re: Helping Someone....

                        Well, he is insistent on pursuing it despite my encouragement to find someone that does it all the time and just pay them. (honestly very hard to find here)

                        So he's just asked for a material list and for me to connect it to the water heater. That's it.

                        I could use some help with the list if anyone wants.

                        About 500 square foot area.
                        Supplemental heat only.
                        Cathedral ceilings with forced air in the ceiling.
                        40,000 BTU NG water heater.

                        List/questions:

                        1000' of half inch PEX?
                        Diffuser plates. Every 3'?
                        Grundfos pump. Size? Stainless? Two pumps with 500' PEX runs/zones?
                        Thermostats?
                        Manifolds?

                        Any help is greatly appreciated.

                        P.S. I called R.E. Michel and another local HVAC distributor today with some questions and they really had no idea what I was talking about. They were asking me more questions than I was asking them & were also like "huh....we don't have any of that."

                        No kidding.

                        Thanks.


                        J.C.

                        Comment


                        • #13
                          Re: Helping Someone....

                          Is he trying to use this heater for domestic as well?

                          He's really going to be disappointed when he goes to take a shower.

                          Comment


                          • #14
                            Re: Helping Someone....

                            Originally posted by plumberscrack View Post
                            Is he trying to use this heater for domestic as well?

                            He's really going to be disappointed when he goes to take a shower.
                            Yes. Think I should have a separate tank for the Master Bath? Just two people. Rarely anyone visiting.

                            P.S. I know what I'm suggesting is not good design. More of "make it work".


                            Thanks for any ideas.


                            J.C.

                            Comment


                            • #15
                              Re: Helping Someone....

                              If anything, it will be good experience. Can you talk to his air techs?

                              Comment

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