Key Takeaways
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Window units: Most installs need just basic hand tools.
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Wall units: Cutting and wiring require extra tools and planning.
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Stay level: A straight unit cools better and drains right.
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Seal it up: Foam and caulk block bugs, water, and heat.
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Use the right circuit: Wall ACs need their breaker to avoid overloads.
Choosing the Right Install Path
Before you grab a drill, decide whether a window or wall unit fits your space, budget, and skill level. A window AC slides into the sash and usually plugs into a standard outlet. A through-the-wall AC sits in a sleeve you cut through an exterior wall and often needs its circuit. Choosing wrong means higher bills or a redo next summer. Check your window’s width, your wall’s framing, and local building codes.
Explore window vs. wall AC units to compare size, sound, and installation needs.
Window AC: Essential Tools Checklist
A window install is straightforward because most supplies come in the box. You’ll need a Phillips screwdriver, a ¼-in. drill, and 1/8-in. bit for pilot holes, plus a tape measure, level, pencil, and scissors. Foam weatherstrip seals tiny gaps and includes L-brackets to keep the sash from slipping. Always lay tools on a towel so screws don’t roll off the sill. Keep a small bowl for hardware; losing a single screw can leave the unit loose and rattling. For extra peace of mind, read our quick central AC install checklist; many safety habits carry over to window jobs.
Window AC: Measure, Mark, and Prep the Frame
Start by finding the exact centre of the sill; a unit placed off-centre can bend the sash over time. Mark with a pencil, then dry-fit the AC without removing the bottom rails. Check that the sill tilts ¼-in. downward outdoors—this lets condensate drip outside instead of onto drywall. If the window frame is vinyl, pre-drill the sash to avoid cracks. Apply the foam weatherstrip along the bottom and side rails before sliding the unit in. A tilted, unsealed install can waste up to 10 % cooling capacity. When you’re sure of fit, lift the AC with legs bent, not your back.
Shop through-the-wall AC systems designed for precise wall framing and clean installs.
Window AC: Seal and Secure for Efficiency
With the unit resting on the sill, lower the sash until it locks behind the top rail. Screw L-brackets into the upper sash to keep kids or pets from bumping it open. Extend accordion side panels, pressing their edges into the frame to block drafts. Tighten panel screws evenly—over-tightening warps thin metal and creates whistles. Fill leftover daylight with scrap foam, then close the window lock. Finally, plug into a grounded outlet and run on high for ten minutes; listen for rattles. If condensation drips inside, your tilt is off—shim the back with a paint stirrer.
Find wall ACs with proper voltage match to ensure safe hookup and long-term durability.
Wall AC: Specialised Tools You Can’t Skip
Wall units cool larger rooms without losing a window view, but they demand more gear. You’ll need a stud finder, a reciprocating saw or jigsaw for the cut, 2×4 lumber for framing, and exterior-grade screws. Add a level, framing square, respirator, and heavy-duty caulk gun. Because the sleeve carries the unit’s full weight, never skip the framing step. Budget an afternoon for cutting and cleanup; drywall dust spreads fast.
Our list of the best window and wall ACs of 2025 shows models with slimmer sleeves that save cutting time.
Wall AC: Cutting and Framing the Opening
Pick a wall section between studs and clear of plumbing or wiring. Mark the outline ¼-in. larger than the sleeve, then score drywall with a utility knife before sawing—this keeps paper edges neat. Cut the sheathing from outside so splinters fall outdoors. Slip a pre-built 2×4 frame into the hole, making sure the bottom plate slopes slightly outward for drainage. Use exterior screws every 8 in. Seal all four corners with flashing tape before sliding in the sleeve. A wobble here causes buzzing later, so re-check the level twice, once before and once after setting the screws.
Wall AC: Electrical and Weatherproofing Steps
Most wall units above 10,000 BTU need a dedicated 120 V or 240 V circuit. If the breaker panel is far, hiring an electrician is cheaper than replacing fried wiring. Feed the cord through a grommet hole in the sleeve to protect against metal edges. Once the chassis is seated, run a bead of exterior silicone caulk around the trim to block wind-driven rain. Inside, patch drywall gaps with setting compound and touch-up paint. For wiring and permit details, compare the process with our article on gas vs. electric furnace installation requirements.
Window vs. Wall AC: DIY vs. Pro Decision
A window install averages under an hour with minimal risk; mistakes are easy to reverse. A wall install can void siding warranties or breach a fire block if mis-cut. Rule of thumb: if you’re comfortable wiring a ceiling fan, you can likely manage a wall unit’s circuit; if not, add pro labour into your budget. Window units are seasonal and portable, making them perfect for renters. Wall units, though pricier upfront, add resale value by keeping sunlight free.
After-Install Care: Quiet, Dry, and Efficient
Once installed, clean the washable filter every 30 days in pollen season. Vacuum coils yearly to stop dust from acting like a blanket. Check caulk or foam each spring; temperature swings can open gaps. For wall units, inspect the sleeve’s drain hole so rainwater doesn’t back up. Listen for new rattles—often a loose bracket or an uneven sill. A five-minute check prevents big repairs.
Grab accessories like foam, filters, and brackets to protect your install and reduce future maintenance.
Frequently Asked Questions
Q: Can I install a window AC sideways to fit a narrow window?
A: No. The compressor relies on gravity-fed oil. Turning it sideways starves the motor and ruins the unit.
Q: How much does a wall AC weigh?
A: Most 12,000 BTU models run 70–90 lb, so plan a second set of hands for lifting into the sleeve.
Q: Do I need a permit to cut a hole for a wall AC?
A: Many U.S. cities require a minor mechanical permit and an electrical inspection—check local code before you cut.
Q: What tilt is correct for a window AC?
A: Aim for about ¼ in. lower outdoors; enough for water to drain but not so steep that vibrations increase.
Q: How often should I replace foam weatherstrip?
A: Inspect yearly and replace if it feels brittle or no longer springs back—typically every 2–3 years.
