Building a Chase for Ductless Split System Air Conditioner Lines

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Ductless, Split System Air Conditioners, or Mini-Splits, are a great option when remodeling. They are great for older homes, built without duct work. Excellent too, as with this Attic, for bringing cooling to locations within a house that weren’t previously cooled.

Mini-Splits are especially easiest when installed on an outside wall. That said, the indoor portion of these systems, the air handler (if you will), can actually set up to 25 feet (including interior space) from the exterior compressor, with little additional effort. Consequently, split system air conditioners work just as well on inside walls. The hurdle here becomes routing and ultimately hiding the system’s line set and condensate line.

Below you’ll find notes related to building a chase for these lines on a Rowhome Attic Remodel. We start by disassembling existing finished drywall (my apologies for no Before pic). We decided to pad out the sides of the passthrough (pictured) as well as the top of the opening. Since we were in an attic, we had the luxury of running lines (at least part of the way) at base of a wall adjacent the attic stair opening. Lines then entered our knee wall at the exact point where we’d go vertical with them. Later we capped that part of the run with a sorta “curb”.

Lines at left later finished with a pvc cover designed specifically for this Sanyo unit

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1. Removing Drywall Corner Beads 

Along the edge of the existing wall, we hit the outside corners of the drywall with a hammer/hammer claw. This effectively cracked up the existing drywall mud. We located corner bead fasteners, either screws or nails, and took appropriate action to remove. (Being conscious of sharp edges on metal corner bead.)

For horizontal surface, we did the same. In our case, we were prepared to use Aviation Snips to cut back the corner bead as far as we needed. But in end we removed the bead from all but the right side of this opening. We’d only remove the “room” side of drywall, but the corner bead from both sides of vertical surfaces. We left the drywall at the top of this opening.

2. Attempting to Identify Header Beam Construction By Viewing the Exposed Corner

As suspected with 2×4 framing (and especially in walls that aren’t load bearing), we found a “built-up beam” (as opposed to an engineered beam).

3. Cutting and Removing Drywall as needed

We planned to remove a narrow strip of drywall from the floor to knee wall “cap”. Measuring approximately 16″ back (we were searching for framing), we found the 2nd stud in the passthrough’s knee wall. We then made a plumb line with a level. In our case somewhere around 10 inches in from the passthrough’s corner. We were trying to catch the inside edge(s) of studs. We then scored both this line and the continuation of the passthrough’s corner (down) with a utility knife. (You actually want to cut the paper.) We then cut the drywall along these lines using a jab saw.

We cut with our saw held on angle while remaining conscious of both wiring and of the “plates” and possible blocking in the wall. If you are nervous about this, flip the breaker off before you begin. The goal here was to make this cut as plumb and perfect as possible. This facilitated easy repair later. We had to remove some screws before we could remove the drywall at the edge of the passthrough. If you are neat enough about this task, you could in theory re-use, otherwise just discard drywall.

4. Framing a “Ladder” for Padding the Header Downward

Well, assembling a ladder (a go-to for bulkheads too) is a topic for another day, but I’ll tell you this. We would choose to assemble ours with deck screws. When deciding on dimensions, we needed to be conscious that since we left the drywall at the top of the passthrough. It would cause this opening to finish a ½ inch lower. The only other note I have on its construction is this. When installing the cripple studs that will make up the ladder rungs, we turned the studs perpendicular to the “rails” and installed them on the outer edge of the plate. In other words, we turned these studs so the wider 3 ½ inch side provides the face for screwing a mounting bracket, drywall, etc.

We spaced all cripples at 16′ oc. with two being 8″ from either side of our center point. On the opposite side, 16″ on center again and also turned, but staggered from those found on the other side. They would NOT line up. We used twice as many rungs, yes, but with the shorties turned and staggered – we gave the HVAC guy an area to “weave” his line set and condensate line through.

5. Installing the Ladder at the Top of the Passthrough

We held the ladder exactly centered in this opening. Since the beam (from step 2) is in fact dimensional lumber (not engineered lumber or yikes steel), we nailed it to the top. You may have to improvise a way to hold it up there until you can get first couple of fasteners in. But you can nail or screw. In our case we shot it in with my framing nailer.

6. Building a “Pocket” – the Chase for Ductless Air Conditioner Lines 

We planned to make our pocket 4 1/2″ wide. We cut a 2×4 to length and set the inside edge of this stud at a mark for 4 1/2″. This new stud would run from the cap of the knee wall to the ladder we installed above. We toenailed this stud into place with 3 1/2″ decking screws at both the top and bottom. (As mentioned in our Screw Guide – love deck screws for miscellaneous carpentry work.)

This formed our pocket. (Later we would insulate for sound). Next, we cut another 2×4 to the size of the framing in the knee wall. This new stud would be screwed to the framing we found earlier (in step 3) when removing our drywall. It acted as the surface to which we’d attach new drywall below.

7. Using a Sawzall We Cut Out Framing that would Block the Pathway for Lines

This is the same technique framers use when framing a doorway in a new wall. We cut out the section 2×4 in the ladder (step 5) and the knee wall cap where our line pocket met them. It should essentially be a 4 1/2″ chunk of 2×4. With that, our HVAC guy will have an unobstructed path in our framing and enough space to bend lines. We cut out a portion of bottom rung in the ladder we just built, and a portion of the top plate in the knee wall that was already there.

Later, we came back and re-added what we took out with a little construction adhesive. This was done after the lines were installed. We also added nailing plates as to protect those lines while we were patching the drywall. The whole thing here – the quickest way to pull it off. This step makes you feel like a real construction dude.

8. Install New Drywall & Corner Bead

Our repair was much more like installing new drywall than any sort of drywall repair Google might return. We cut and hung our patch. Taped and installed corner bead. (Maybe one day I’ll write an article about this type of task.)

9. Finish Newly Installed Drywall & Paint

Again a topic for another day.

More Moxie (Related Links and Additional Info)

Note: When it came time for our hvac guy to install the line set and condensate line, he did not use the horizontal portion of the chase described above (the ladder – steps 4 and 5). He opted to poke thru the wall instead (as pictured), and we finished later with a manufacturer’s specified trim kit. His reasoning; with the interior unit, the lines and their connections to the unit must remain accessible for easy service. Regardless, as you can see in the picture, we needed the extra surface area created by the ladder for mounting the unit anyway.

Great information here about Ductless, Split-System Air-Conditioners from Old House Web.

We’ve discussed Ductless HVAC a few more times on the blog. First in the article – Remodeling a Bungalow.  A few years later, We Toured the Home of Chris & Jodi, architects @ LG Squared. Enjoy and thanks.  ~jb