Key Takeaways
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Pick the spot: Use a shaded wall with 12–24" outdoor clearance.
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Frame it right: Use 2×4s and a header to support the wall.
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Cut carefully: Make the hole ¼" bigger than the sleeve, with a slight outward slope.
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Seal it tight: Insert the wall sleeve, insulate gaps, and caulk inside and out.
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Power check: Use a dedicated 120V or 230V outlet—match the unit’s label.
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Finish clean: Add trim and flashing to block rain, air leaks, and bugs.
Why Strong Framing Matters
Imagine hanging a 70-pound backpack on one sheet of drywall—it would rip right out. A through-the-wall AC is that backpack. Without solid lumber framing, the unit sags, makes noise, and leaks cold air into the studs. In this guide, you’ll learn the same framing steps HVAC pros use so the appliance cools quietly for 10-plus years. We’ll cover choosing the wall, measuring for the sleeve, building the frame, sealing, wiring, and easy upkeep—all in plain language a middle-schooler can follow but detailed enough for serious DIYers.
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Picking the Perfect Wall Spot
Start with a true exterior stud wall, never an interior partition. Check the compass: north- or east-facing walls stay cooler, so the compressor doesn’t bake in the afternoon sun. Make sure bushes or decks give you a clear 12- to 24-inch airflow corridor outside. Indoors, pick a spot near the center of the room and away from shelves that could block supply air. Finally, locate a nearby outlet on the proper voltage circuit—many 8,000 BTU units are 120 V, while 12,000 BTU and above often need 230 V. If the breaker panel is full, plan on hiring an electrician before you cut wood.
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Measuring Twice, Cutting Once
Every manufacturer lists exact sleeve dimensions, but a common size is 26 in W × 15 in H. Mark studs with painter’s tape, then add ¼ in clearance all around for foam insulation. Measure again from multiple reference points—the floor, ceiling line, and adjacent window so the grill looks level after install. Remember to include drywall thickness: a flush mount on a ½-in sheet means your rough opening must account for that layer. Keep a framing square handy; even a small skew can jam the sleeve during insertion and ruin your day.
See detailed sizing advice in our Best Window and Wall ACs of 2025 guide
Building a Strong, Safe Frame
Cut drywall with a stud finder and keyhole saw, then expose two vertical studs. Next, install a 2 × 4 or 2 × 6 header across the top—this “mini-lintel” prevents sagging siding and cracked plaster. Toe-screw jack studs beneath the header and cripple studs above if you sever any load path. Use exterior-grade screws (not nails) so vibrations don’t loosen joints. Dry-fit the sleeve: it should slide in smoothly and sit ⅛ in low on the outside edge to promote drainage. Any wobble now will become rattling later.
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Sliding in the Wall Sleeve at the Right Angle
The sleeve is the unsung hero—it carries weight, directs water, and simplifies future swaps. Before pushing it home, place a ¼-in shim on the interior sill and a level outside. Aim for a 6-degree slope (¼ in per foot) so condensate flows outward, never backwards. Fasten the sleeve to studs with rust-resistant screws through factory holes. If you need a deeper sleeve extension kit, order one rated for the exact model to avoid restriction of the discharge air path.
According to our 12,000 BTU maintenance checklist, these 10-minute tasks can extend compressor life by 3–5 years
Sealing & Insulating for Year-Round Efficiency
Energy loss happens in finger-wide cracks. Push low-expansion spray foam around all four sides, stopping ½ in shy of the face to avoid bulges. Once cured, shave flush with a utility knife and finish with interior trim or J-channel outside. Run a continuous bead of silicone caulk along the sleeve lip, the siding joint, and any screw heads. This step blocks noise, pollen, and winter drafts just as much as it prevents rain leaks.
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Wiring & Safety Checks You Can’t Skip
A through-the-wall AC can draw 7–12 amps on cool and even more in heat mode. Verify that the circuit breaker is sized correctly (usually 15 A for 120 V units, 20 A for 230 V). Never use an extension cord voltage drop overheats compressors. Test the GFCI or AFCI as required by the latest National Electrical Code. If your home wiring is aluminium or ungrounded two-wire, schedule an electrician before first startup to avoid voiding the manufacturer’s warranty.
For efficiency math, check our SEER2 explainer.
Finishing Touches That Keep the Weather Out
Install metal drip flashing over the top trim and lap it beneath the existing siding. Paint raw wood and caulk joints to keep termites and moisture at bay. Indoors, fasten a colour-matched trim ring or wood casing around the grill to hide foam edges.
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Easy Maintenance to Make Your Wall AC Last
Set a phone reminder every month in summer: pull the filter and rinse it under the faucet. Twice a season, vacuum the coil fins with a soft brush and inspect the outside grille for leaves. When you winterize, close the front louvers, pop in an insulated cover, and check that the caulk bead hasn’t cracked.
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Frequently Asked Questions
Q: Can I put the unit in a load-bearing wall?
A: Yes, but you must add a properly sized header and jack studs to transfer the load. If you’re unsure, get a carpenter’s advice.
Q: How much outward tilt is enough for drainage?
A: About ¼ in per foot of depth—usually a ⅜ in drop from inside to outside for standard sleeves.
Q: Do I need extra insulation around the sleeve?
A: Yes. Low-expansion foam fills gaps without warping the frame, keeping hot air and insects out.
Q: What’s the best BTU size for a 300 sq ft room?
A: Roughly 7,000–8,000 BTU, but check the sizing chart in our 15-inch window AC guide for fine-tuning
Q: Can I run the AC on a regular 15-amp bedroom circuit?
A: If the nameplate says 120 V and ≤ 12 A, yes—but avoid plugging in other heavy appliances on the same circuit while it’s running.
