🧰 Introduction: Why Proper Installation Matters
Hi folks — Tony Marino here. Installing a through-the-wall air conditioner can seem straightforward at first glance: cut a hole in the wall, slide the unit in, plug it in, and you’re set, right? Well, not quite.
The truth is that how you install the unit has a huge impact on its performance, lifespan, energy consumption, and even safety. Poorly installed ACs can lead to:
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Drafts and energy loss
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Water leaks and mold
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Excessive noise or vibration
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Premature equipment failure
And let’s face it — nobody wants that.
In this guide, I’ll cover all the best practices you need to know before installing a through-the-wall unit yourself or even before you hire a pro. I’ll touch on everything from choosing the perfect wall location to sealing up the sleeve properly and making sure the drain works like a charm.
Let’s jump in.
🏠 Step 1: Choose the Right Wall and Location
Your first and most important decision is where you’re going to put the unit. Think carefully because you won’t want to move it later!
Here’s what to look for:
✅ Exterior wall: Pick a true exterior wall with enough structural integrity to support the weight of the AC.
✅ Shaded area: Whenever possible, choose a wall that’s shaded during the hottest parts of the day. Avoid south- or west-facing walls that get blasted by direct sunlight — unless you want the unit working overtime!
✅ Away from obstructions: Leave at least 12–24 inches of clearance outside around the back of the unit for proper airflow. Avoid shrubs, walls, or debris too close to the outside grille.
✅ Electrical access: Have a dedicated electrical outlet nearby that matches the AC’s power requirements. If you need help understanding voltage requirements for your model, check out this energy.gov article on AC energy consumption and electrical load.
✅ Consider noise: Choose a wall that’s away from bedrooms or quiet spaces if the sound of the compressor might bother you or your neighbors.
📏 Step 2: Measure Carefully Before You Cut
Once you’ve picked your spot, carefully mark and measure the wall cutout. Remember, most through-the-wall ACs require a slightly larger opening than the unit itself so you can fit a sleeve that supports the unit and insulates the edges.
Here are some pro-tips for the cut:
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Check your wall type: Wood-framed walls will need framing reinforcements. Masonry walls will require a specialized saw and masonry anchors.
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Double-check inside and outside: Confirm there are no hidden electrical wires, pipes, or structural studs where you plan to cut.
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Cut with the right tools: A reciprocating saw or a circular saw is common for wood framing. For masonry, rent a masonry saw or hire a contractor if you’re not comfortable.
If you’d like to read more about safe structural modifications and code compliance, this article from Green Building Advisor covers best practices for framing walls properly and keeping your home efficient.
🧭 Step 3: Install a Proper Wall Sleeve
A wall sleeve is a metal or plastic box that fits into the wall and holds the AC unit securely. Many homeowners skip this — big mistake. Installing a sleeve provides structural support, creates a proper seal, and lets you easily remove or replace the AC in the future.
When installing the sleeve:
✅ Slide it in level: The sleeve must fit snugly and sit perfectly level. Use a long level and shim as needed.
✅ Slight tilt to outside: Allow a slight outward tilt (¼ inch per foot is typical) so water drains outside properly.
✅ Seal the edges: Fill gaps around the sleeve with foam insulation, then caulk the outside edges.
If you’d like more guidance on the refrigerants and safe handling that modern AC units require — especially if you’re dealing with newer refrigerants like R-32 — check out the EPA's refrigerant handling guidelines. Following these is critical if you ever plan to service or dispose of your unit.
🧰 Step 4: Proper Support and Bracing
Through-the-wall ACs can weigh 60–120 pounds or more. Even if your wall is strong enough structurally, the weight of the unit can cause sagging or bowing over time if it’s not properly supported.
Here’s how to do it:
✅ Add supports under the sleeve: Many manufacturers recommend using steel or wooden supports beneath the sleeve, anchored into wall studs.
✅ Brackets outside: Consider installing an exterior support bracket or platform that cradles the unit outside.
✅ Check the manual: Every unit is different. Some come with brackets; some require you to buy them separately.
For more information on proper mounting and efficiency requirements, take a look at this article on HVAC energy standards and installation requirements by AHRI. Following these guidelines will help you protect your unit's lifespan and efficiency.
🔧 Step 5: Insulate and Weatherproof
Insulating around the AC is one of the most overlooked — and most important — installation steps. A leaky seal will drive up your energy bills and can let pests or water into your wall cavity.
✅ Spray foam or batt insulation: Fill all remaining gaps around the sleeve with low-expanding spray foam or fiberglass batt insulation.
✅ Weatherstripping: Apply durable exterior caulk around the outer sleeve edge. Make sure water cannot penetrate where the sleeve meets the wall.
✅ Cover panels: Some ACs come with insulation panels for inside the sleeve to reduce drafts around the sides of the unit.
Proper sealing is also your first line of defense against humidity intrusion, which can lead to mold. This article from ENERGY STAR on air-sealing and insulation contains more practical advice for creating a tight, energy-efficient installation.
⚡ Step 6: Handling the Unit Safely and Installing It into the Sleeve
With the sleeve properly installed and sealed, it’s time to slide the AC unit into place.
Here’s the safe and correct way:
✅ Have help: These units can be heavy — don’t risk an injury. Have a partner help you slide the unit in carefully.
✅ Use care with refrigerant lines: Modern units use eco-friendlier refrigerants like R-32. They’re efficient and safer for the environment, but they’re also mildly flammable. Treat the unit gently and follow all handling safety guidelines.
✅ Secure the unit: Once it’s slid into place, use the screws or brackets provided to anchor the unit to the sleeve.
And remember — if you ever need to troubleshoot refrigerant leaks or do repair work, it’s usually best to call a certified HVAC pro.
🧼 Step 7: Test It and Maintain It
Once installed, plug the unit in and do a test run:
✅ Test all modes: Check cool, fan, and energy saver modes to make sure they all work properly.
✅ Check water drainage: Pour a small amount of water into the drain pan and make sure it exits outside.
✅ Inspect for drafts: Feel around the edges of the sleeve and unit for drafts. Seal any that you find with foam or caulk.
Going forward, plan to clean the air filters every few weeks during cooling season and inspect the drain every year. Taking care of your unit will maximize its efficiency and lifespan.
🧑🔧 When to Call a Pro
While DIY installation is doable for handy homeowners, you might want to call in an HVAC pro if you encounter:
❌ Structural challenges: Reinforcing masonry walls or rerouting electrical wires
❌ Refrigerant handling: Only EPA-certified techs can legally recover or service refrigerants like R-32.
❌ Drainage issues: If you can’t get a proper exterior drain slope or worry about water damage
And if you’d like help finding a certified pro who’s experienced with refrigerants like R-32, you can visit the EPA's Section 608 Technician Locator to find a certified technician in your area.
✅ Conclusion: A Solid Installation Means a Happy Home
There you have it — my top installation tips and best practices for putting a through-the-wall air conditioner into place. Do it right, and your unit will:
✅ Cool efficiently all summer long
✅ Last for years without repair
✅ Keep your energy bills under control
✅ Protect your walls from leaks and drafts
And if you ever need help choosing the perfect model or getting expert advice, you can shop The Furnace Outlet’s through-the-wall AC collection, where we offer a range of models and guidance to match any space and any need.
✍️ About the Author
Tony Marino is an HVAC veteran with over 20 years of hands-on experience. Known for his practical, honest advice, Tony enjoys helping homeowners make smart HVAC decisions that improve comfort, save money, and reduce hassle.
