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Community and Q&A

Installing Refrigerant Tubing to be Heat Pump Ready

dylan_lamar | Posted in Mechanicals on

I’m in construction on a small affordable housing 6-plex with one-bedroom units. The budget won’t allow for 6 mini-split heat pumps at this time so we’re doing electric cove heaters initially (pretty standard for affordable housing here in Oregon). We’re pre-wiring for a future heat pump retrofit but I’m also wondering if anyone has experience pre-installing the refrigerant tubing in the walls?

I’ve self-installed a heat pump before and the problem I’m seeing is what to do with the ends of the copper tubing at each end. From my memory we needed a foot or more of tubing protruding from the wall at each end to make the install, but this can’t be abruptly bent or rolled out of the way the way wiring can. Is it feasible to cut the tubing just behind a drywall access panel and have the future HVAC installer sweat/solder a connection here? And a similar approach at the exterior?

I’d love to propose a workable solution like this to the local heat pump store.

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  1. Expert Member
    BILL WICHERS | | #1

    First, your installers should be BRAZING fittings, not SOLDERING. This is actually a code issue. Soldered connections fail at lower temperatures which is a problem in fires.

    I don't see a problem leaving the lines in the walls, but I'd either braze on a connector, or use a flare connector, then put caps on the lines. You don't want contaminants getting into the lines while they're hidden away. If it was my install, I'd run dry nitrogent through the lines too, then put caps on, which would keep an atmospheric pressure charge of nitrogen inside the lines while they're "stored" in the walls.

    If you assume the wall unit will cover an access hole, you could leave a coil inside the wall knowing that you'd be cutting a hole in the wall later to get to the coil. The wall-mount heat pump unit could then be used to cover that hole (assuming you don't need the drywall as an air barrier at that location).

    A skilled installer could probably braze a 90 degree fitting on through a relatively small opening in the wall if you can't store much slack. If the stud cavities are open, you could form the tubing into a loose "S" or wave shape between the studs, then DON'T strap the tubing in place. In the future, you could cut a small access hole, then stretch out the wave and that would serve as your slack storage. If I were to try this, I'd leave a blank electrical plate installed in the wall where the lines were to come out, and I'd use a "low voltage ring" to secure that blank cover plate to the wall. Tie a string to the end of the lineset, then tie that string to the low voltage ring. This gives you an easy way to get the end of the tubing out without hunting around inside the wall. If you don't have the end of the tubing tied off, it will want to spring back into the wall somewhere difficult to reach from the hole. Trust me on this, it will KNOW where the hardest spot to reach is, and that's where it will go ;-)


  2. charlie_sullivan | | #2

    I'm inclined to suggest putting in some kind of conduit that you could install refrigerant tubing into at a later date...or use to install water tubing if it turns out that an air-to-water system makes sense at that point. Or maybe we'll have CO2 refrigerant systems that need high-pressure lines, different from the standard soft copper you'd use now.

  3. lukasmpeter | | #3

    Did you talk to somebody at Energy Trust of Oregon?
    You may be able to get incentives for the minisplits that allow you to skip the resistance heat.
    I am working with them on several projects and find them incredibly helpful.

  4. jameshowison | | #4

    Risinger did a recent episode of "future proofing" access through air-sealed walls, using flashed conduit with a threaded connection. He put them up under gable end eaves. Does seem that something like that would be easier. It's in the "real rebuild" series called, "$20 Future-Proofing Trick!"

    But is the issue wanting to have the lines snake through the walls? Yeah, I reckon something like blue "smurf tube" on the route would work, giving long radius turns?

  5. dylan_lamar | | #5

    Thank you all for the feedback. I think having a connector available immediately behind an access hole would be ideal. The walls will be filled with dense-pack cellulose so while I like the approach of leaving an excess "S" shape in the wall, this would be problematic.

    Conduit is a good idea too. It might work for some of the more direct runs without too many bends. Or if I bite the bullet and assume some amount of surface mounted chaseway on the exterior, allowing a relatively straight conduit run to finish the route.

    I'm in Eugene which is not ETO territory unfortunately, and the local utility provider's incentives for heat pumps are sorely lacking.

    1. Expert Member
      BILL WICHERS | | #6

      If you put in something like tyvek between the dense pack cellulose and the drywall, you might be able to hide your "S" of tubing between the tyvek and the drywall.

      I wouldn't try to pull refrigerant lines inside of smurf tube, or any other flexible conduit for that matter. Pulling wire in flexible conduit is MUCH more difficult than pulling inside of rigid conduit, and pulling something that's already pretty stiff like refrigeration tubing will be even harder to pull in.


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