Installation Guide: What Samantha Learned Before Cutting a Hole in the

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Hi there! I’m Samantha. When I first decided to install a 15,000 BTU through‑the‑wall AC unit, I thought it would be as easy as popping it in a window. But once I started researching, I quickly realized there’s a lot more to it — from sizing and placement to electrical work and wall safety.

Cutting a hole in your home is a big decision. So before you start, let me walk you through what I learned the hard way (and what I wish I’d known sooner).

📐 Step 1: Sizing & Placement Comes First

Why BTU Sizing Matters

A 15,000 BTU unit is designed for larger rooms — typically 700–850 square feet. But oversizing can cause short cycling (turning on/off too often), while undersizing leaves you sweating.

🔹 General guideline from Energy.gov:

150–250 sq ft → 6,000 BTUs
250–350 sq ft → 8,000 BTUs
350–550 sq ft → 12,000 BTUs
550–850 sq ft → 15,000 BTUs

Where to Place the Unit

Choose a central exterior wall for even airflow.
Avoid walls shaded by trees if possible — ACs need ventilation.
Stay away from areas with plumbing, wiring, or gas lines.

💡 Samantha’s tip: I used a stud finder to check my wall and even peeked at old floor plans before deciding.

🧱 Step 2: Checking Wall Type & Safety

Not every wall is suitable for cutting.

Load‑Bearing Walls

Cutting into these walls can compromise your home’s structure.
May require headers, reinforcements, or professional framing work.

Non‑Load‑Bearing Walls

Best choice for AC installation.
Still need a sleeve for support, but safer to modify.

How I Checked Mine

I tapped along the wall, checked my attic for support beams, and confirmed with a local contractor that my chosen wall was non‑load‑bearing.

🔗 Resource: Family Handyman’s guide is excellent for identifying load‑bearing walls.

⚡ Step 3: Understanding Electrical Requirements

Here’s the part I underestimated!

Voltage Needs

Many 15,000 BTU units require 230V outlets.
Standard U.S. outlets are 115V — so I had to call an electrician.

Dedicated Circuit

High‑capacity ACs often need a dedicated 20‑amp circuit.
Prevents tripping breakers when running with other appliances.

My Lesson Learned

I budgeted for the unit but forgot about the $350 electrician bill to install the outlet. Plan for this upfront!

🔗 Reference: Energy Star room AC guidance highlights checking voltage before purchase.

📦 Step 4: Choosing the Right Wall Sleeve

Why It’s Crucial

Provides structural support for the AC.
Prevents air leaks, moisture intrusion, and noise.
Required for warranty on most models.

Types of Sleeves

Manufacturer‑specific sleeves: Designed for a particular brand/model.
Universal sleeves: Fit multiple brands but may require trim adjustments.

💡 Samantha’s advice: Don’t try to reuse an old sleeve unless the manufacturer confirms compatibility. My dealer insisted on the matching sleeve, and I’m glad I listened — no drafts at all!

🔗 The Furnace Outlet’s wall sleeve guide explains how to pick the right size.

🛠️ Step 5: Tools & Skills You’ll Need

Before you cut, make sure you have the right gear:

Reciprocating saw or jigsaw (for siding & drywall)
Level & measuring tape (for a square cut)
Stud finder (to avoid hitting studs, wires, or pipes)
Caulk & insulation foam (to seal gaps)
Drill, screws, and anchors (to mount the sleeve)
Safety gear: gloves, goggles, dust mask

💡 Samantha’s note: I’m handy, but I still had a carpenter help with the actual cutting. The sleeve and sealing were DIY-friendly.

🧰 Step 6: Step‑by‑Step Prep Work

Here’s how I approached it:

Measure the unit & sleeve dimensions carefully.
Mark the opening on both interior and exterior walls.
Cut inside drywall first, checking for wires/pipes.
Cut exterior siding using a reciprocating saw.
Install the wall sleeve, ensuring it’s level and sloped slightly downward for drainage.
Slide in the AC unit, securing it with provided brackets.
Seal gaps with caulk and insulation foam.