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Pex-AL-Pex Connectors for Heat Pump

bliksem | Posted in General Questions on

I am due to install an Arctic Heat Pump solution for radiant floor heating, cooling and domestic hot water.

My soldering skills are sorely lacking and can become quite costly with mistakes. The connections between the HP, boiler, buffer and valves are 1 1/4 and 1 inch NPT.

I looked at Shark Bite copper connectors but cannot ignore the fairly common warnings on the failure rate of these.
Can I use Pex-AL-Pex to connect between these?

Thank you for taking the time to read.

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  1. DC_Contrarian_ | | #1

    You can. You can also use oxygen barrier PEX, which I find easier to work with.

    The problem with PEX is the cost of the tools, and as you get into bigger sizes it becomes hard to find and expensive. How much 1-1/2" do you need to do? Can you do that in threaded brass and then transition to 1" PEX? Or do it in 1-1/2" copper, and pay someone to solder it for you?

    This is the 1" oxygen barrier PEX I like to use:

    This is a reasonably priced 1" crimper that I've had good results with:

    1. DavidDrake | | #4

      @ DC_Contrarian,
      Not a plumber, just a homeowner brave/stupid enough to run my own plumbing (FWIW, it's all passed inspection).

      That looks like a nice price on a copper ring crimper. I bought a stainless ring crimper a few years back, mainly because a single tool can crimp multiple diameters of stainless rings. Prior to that, I used copper rings and rented crimp tools.

      Is there a problem with stainless rings vs. copper, other than higher cost for the rings?

      And yes, I realize this is a question I should have asked a while back, before I went and ran a bunch of plumbing with stainless rings :).

    2. bliksem | | #6

      Apologies for the very late reply, I did not get an email notification someone had responded to this.

      What I have read is that Pex A is more flexible but suffers greater pressure loss. The 1 inch runs should be very short between the heat pump, boiler and buffer tank (less than 5 feet each). The 1 inch run from there to the manifold will be 20+ feet.

      I also read that Pex A handles Sharkbite EvoPex connections very well and has a 25 year warranty. It actually works out cheaper than buying brass compression fittings if you can believe that.

      So if Pex A pressure loss is not a worry, then cheaper and easier EvoPex fittings are very appealing.

  2. Expert Member
    Akos | | #2

    I find PERT is much easier to use for larger pipes, much flexible than PEX. Pex Al Pex is way too hard to work with.

    I would not use any 1 1/2" unless you have very long runs or huge flow rates. Size the pipe for your actual flowrate, much easier and cheaper to use a reducing bushing and smaller pipe than having to deal with those big pipes.

    1. DC_Contrarian_ | | #3

      Yeah, the first step is to find out whether you really need pipe bigger than an inch. I would run your piping diagram past the manufacturer and ask what pipe size you really need. Even if the fixtures have bigger connections it's easy to use a bushing to adapt them down.

      To do your own rough calculations there are two things you have to worry about. One is not running the water through the pipe too fast, which can cause noise and wear. The rule of thumb is you shouldn't exceed 6 feet per second. Pex at 3/4" is 1.38 gallons per hundred feet, 1" is 3.03 and 1-1/4" is 6.38. That corresponds to 5 gpm, 11 gpm and 23 gpm.

      The biggest Arctic heat pump is 42K BTU/hr. The formula for heat transfer is GPM times temperature drop times 500. So with 3/4" PEX you'd need 16.8F temperature drop, 1" is 7.6F and 1-1/4 is 3.7F. I'd bet the temperature drop is at least 10F, which means you need 8.4 GPM of flow and 1" is fine for that.

      The other aspect is that the pipe has to provide no more resistance than your circulator pump can overcome at the desired GPM. This is a more complicated calculation, it depends on the pump being used. This is where the manufacturer can help you.

      One inch pipe is a lot easier to work with, for example the insulation is a big-box store item.

      1. bliksem | | #7

        Thank you very much for those numbers! I could not have put that together myself. I have the Arctic Heat 060ZA/BE.

        Sounds like 1 inch could be the ticket with my Grundfos 26-99 (0-30g/pm) at the heat pump and Grundfos Alpha2 15-55 at the manifold (0-19 g/pm)?

        1. Expert Member
          DCcontrarian | | #8

          On the spec sheet it says 13 GPM and more important, the unit itself has 1" connections. At 13 GPM 1" is a little undersized, that comes to 7.15 feet per second for the water speed in the pipe, which is above the guideline of 6 feet per second but not outrageously so. If your runs are short that shouldn't be a problem.

          The bigger question is whether your circulator pumps can push 13 GPM through your piping. That's harder to predict, there are ways to model it but often the thing to do is build it and see. That heat pump is rated at 60K BTU/hr, at 13 GPM it has a 9.2F temperature rise. If you can't get the rated water flow you're not going to get the rated BTUs. In an extreme case you can damage the heat pump if the water flow is too low.

          The flow through the emitters -- radiators and radiant tubing -- is going to be variable depending on the number of zones calling, so typically a system like this will have a buffer tank to absorb the excess flow when not all zones are calling. So really what you care about is the piping between the heat pump and the buffer tank, if that can handle 13 GPM with the pump you have you're set. And that's easy to test. Does the heat pump itself have a flow meter? I have a Chiltrix and it reads out GPM for me.

          1. bliksem | | #9

            I should check - there is a dial on there but I have not paid close enough attention to see what it is.

            There is a buffer tank. The piping between the heat pump and the buffer tank (and altsource boiler) are all 1 inch (see attached design pdf). The entire downstairs is one zone and upstairs has 4 zones

    2. bliksem | | #5

      Apologies for the very late reply, I did not get an email notification someone had responded to this.

      I had not heard of PERT until now, thanks. My initial plan was to install a 1 1/4" to 1" brass coupling to the boiler nipples and then connect 1 inch pipe (I think that is the same as a reducing bushing). When I originally looked at pex-al-pex, I knew it was hard to work with from the 1/2" Warmboard pipe install. So 1 inch must be even harder.

      What I have read is that Pex A is more flexible but suffers greater pressure loss. The 1 inch runs should be very short between the heat pump, boiler and buffer tank (less than 5 feet each). The 1 inch run from there to the manifold will be 20+ feet.

      Does PERT suffer the same pressure loss? Is this even a consideration with runs this short?
      As for flow rate, Arctic Heat sized a Grundfos 26-99 for the heat pump (0-33 g/pm) and a Grundfos Alpha2 15-55 for the manifold/floor (0-21 g/pm).

      I apologize if I am missing pertinent information to respond to this, I am very green on this.

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