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 Remodel, for bringing cooling to spot locations within a house not previously cooled.

Mini-Splits are especially easy to install on an outside wall. That said, though, the inside portion of these systems, the air handler, can actually set up to 25 feet from the exterior compressor with little additional effort. Consequently, Split System Air Conditioners work just as well on inside walls. The hurdle here becomes hiding the system’s “line set” and condensate line.

Below you’ll find notes related to building a chase for these lines on the Fells Point Attic Remodel linked above. We start by disassembling existing finished drywall (my apologies for no Before pic). We had to pad out both the side of the passthru (pictured) and the top of the opening.

Estimated project time- 4 to 6 hours

Material and Tools listed at bottom.

Split Unit Inside Wall Condensate Lines Unfinished

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

1. Remove corner beads from horizontal surface and top most portions on drywall (8″ from top) on verticals on pass thru opening. (You may have to cut the corner bead on side with Aviation Snips.) Do this by hitting outside corners of drywall with hammer/hammer claw to crack existing drywall mud. Locate corner bead fasteners, either screws or nails and take appropriate action to remove (be conscious of sharp edges on metal corner bead). Discard.

2. Attempt to identify beam material by viewing the exposed corner

3. Cut and remove drywall – entire section from floor to knee wall cap. Measure approximately 8″ (or where you are certain no framing exists). Start this process by making a plumb line with a level – 8 inches in from the corner. Then score both this line and the corner with your utility knife. (In the corner you actually want to cut the paper.) Cut the drywall along the line you made using the hand held drywall knife.

Cut with knife held on angle while remaining conscious of both wiring and the top and bottom horizontal plates of the wall. If you are nervous about this, flip the breaker off before you begin. Your goal here is to make this cut as plumb and perfect as possible. This will facilitate easy repair later. You may have to remove some screws before you remove drywall. If you are neat about this task, we can re-use, otherwise discard drywall.

4. Frame ladder that will pad beam downward. Well, you saw how we constructed a ladder before. I would choose to assemble with screws, and be conscious of the fact that drywall will cause this opening to finish a ½ inch lower. The only note I have on its construction is this- when installing the cripple studs that will make up the ladder rungs. Turn the studs perpendicular to the rails and install on the outside edge of the rail. In other words, turn the stud so the wider 3 ½ inch side provides the face for screwing mounting bracket, drywall, etc.

On the street side of the ladder, space all cripples at 16 oc. with two being 8 from either side of your center point. On the opposite side, 16 on center and turned, but staggered from those found on the alley side. They should NOT line up. You will be using twice as many rungs, yes, but with studs turned and staggered; you will give the HVAC guy an area to weave his Freon lines through. If you follow – good, if not – ask.

5. Install ladder at top of pass thru. Try to hold the ladder exactly centered in this opening. This will give you a better finish on the drywall. If the beam (from step 2) is in fact dimensional lumber (not engineered lumber or steel) nail 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. You can nail or screw, but if I were to come, we could shoot it in with my framing nailer. If the existing beam is engineered lumber and or steel – you should glue it at the top and nail to the sides. Be conscious of wiring for lights.

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6. Build pocket for lines – This will occur on the Eastern Ave side of pass-thru. Despite what I said earlier, you are going to use 2x4s and span the width of the opening. In other words, the 3 ½ inch side will point at Wolfe & Anne (can’t figure a better way to put this). Cut to size and nail 1st 2×4 to the Eastern Avenue side of the opening. Next cut another to the same size and install 4 inches inward in the alley-side direction. This will form your pocket. (Later we will in insulate for sound). Fasten using screws or nails – you might have to toenail. Screw the interior 2×4 at both the top and the bottom.

7. Use the Sawzall to cut out 2×4 stock that blocks our path – This is the same technique framers use when framing a doorway in a new wall. I want you to cut out the 2×4 that appears between the 2 studs in our line pocket (Step 6). It should essentially be a 4 length of 2×4 – With that our HVAC guy will have an unobstructed path in our framing. You are cutting out a portion of bottom rung in the ladder you just built, and a portion of the top plate in the knee wall that is already there. You can do this and get away with because the 2nd interior 2×4 in the pocket is now providing some structure.

Later, we will come back and put another 2×4 and construction adhesive in the knee wall before we patch the drywall on the street side (step 3). It is the quickest way to pull this off – and trust me; this step will make you feel like a real construction dude.

8. Install new drywall and corner bead – Only on Wolfe side and bottom of the new framing. Let me know if you need some tips on this.

9. Finish newly installed drywall – Again let me know if you need some tips on this.

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 (steps 4 and 5). He opted to poke thru the wall instead, and we will finish later with a manufacturer’s specified trim kit. His reasoning; with the interior end of the split unit — the lines and their connections to the unit must remain accessible for easy service.

>> More Moxie (Related Links and Additional Info) :

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


(5) 2x4x92 5/8 (if cost dictates)
2 1/2 inch deck mate screws
16d framing nails
Drywall (enough for patch)
1 1/4 to 1 5/8 in. drywall screws
(2) 1 1/4 inch drywall corner bead – 8ft lengths
1 3/8 drywall nails
1 tube liquid nails
Caulk gun
Drywall Mud
Drywall Tape


Aviator Snips
4′ level
Punch/Keyhole/Drywall Saw
Utility Knife
Tape Measure
Miter or Circular Saw
Screw Gun
Drywall Tools