💁 Samantha’s Friendly Hello
Hey there — Samantha here, your HVAC-loving neighbor who’s all about making home comfort easy and accessible! 🤗 Installing a through-the-wall AC is one of those projects that can feel super empowering… until you hit a snag. Trust me, I’ve seen my fair share of “oops” moments over the years — from holes cut too big to ACs installed without a proper seal.
And those mistakes? They can add up fast — higher energy bills, water leaks, noisy operation, or even long-term damage to your walls. Not exactly the kind of “cooling off” you hoped for, right? But hey — don’t stress. I’m here to help you sidestep those pitfalls before they happen.
In this guide, we’ll go over the most common installation mistakes, what they mean for your home, and — most importantly — exactly how to avoid them. With clear explanations and helpful links to trusted expert advice, you’ll have all the info you need to install your AC the right way, the first time. Ready to make your summer smooth and stress-free? Let’s jump in! 🌬️💪
🔨 1️⃣ Mistake #1: Not Measuring the Wall Properly
Before you touch a saw, you need accurate measurements — both inside and outside.
❌ The Mistake: Guessing the size of the wall opening and leaving too much or too little room.
✅ How to Avoid It: Double-check the unit’s sleeve dimensions and add a tiny buffer — about a quarter-inch for wiggle room. York NYC has an awesome step-by-step measuring and cutting guide that breaks this down further.
⚡ 2️⃣ Mistake #2: Forgetting the Dedicated Circuit
Through-the-wall units often need a dedicated circuit, especially larger ones.
❌ The Mistake: Plugging into an existing outlet that can’t handle the load.
✅ How to Avoid It: Check the BTU requirements — most ACs over 10,000 BTUs need their own 115V or 230V line. Consumer Reports offers a handy overview of AC power requirements in their AC buying guide to help you plan.
🧰 3️⃣ Mistake #3: Ignoring Proper Wall Support & Tilt
Every AC needs a slight tilt so water drains outside — and the right wall support so it stays secure.
❌ The Mistake: Installing perfectly level or not supporting the unit’s weight with brackets.
✅ How to Avoid It: Frame the opening properly with 2×4s and follow the manual’s drain tilt specs. This Old House outlines this perfectly in their article on installing a wall air conditioner, especially the part on drainage.
🧩 4️⃣ Mistake #4: Skipping Weatherproofing
A tight fit matters — without caulk and insulation, your AC opening could leak air and water.
❌ The Mistake: Leaving gaps between the wall sleeve and the wall.
✅ How to Avoid It: Use spray foam insulation or caulk on all gaps and cover with trim to seal against rain. The U.S. Department of Energy shares useful weatherization basics to help you make sure your install stays airtight.
🔇 5️⃣ Mistake #5: Ignoring Vibration Dampening
That rattle you sometimes hear? It’s caused by improper bracing or not using rubber pads.
❌ The Mistake: Letting the unit sit metal-to-metal in the sleeve — hello noise and wear!
✅ How to Avoid It: Add rubber shims or anti-vibration pads during install. Soundproof Cow discusses simple ways to minimize noise in a soundproofing an AC unit article — a must-read for bedroom installs.
💖 Samantha’s Friendly Outro
And that’s a wrap on my top installation mistakes to avoid! 🎬💖 Installing a through-the-wall AC is one of those jobs that can go really smoothly if you prepare, measure carefully, and follow a proven plan — and I just handed you that plan. From making sure you have the right power setup to caulking every tiny gap, these steps will help you skip the headaches and enjoy all that wonderful, worry-free cool air.
Still deciding on the perfect unit for your space? Check out The Furnace Outlet’s full collection of through-the-wall ACs — they have something for every size, style, and budget.
Thinking of getting some accessories for your unit? Visit my guide: Covers, Insulation Kits & Noise Dampeners for a Super-Cozy, Ultra-Quiet Through-the-Wall AC.
Thanks so much for sticking with me — your gal Samantha is cheering you on every step of the way. 🙌💖 Don’t hesitate to bookmark this checklist or pass it along to a fellow DIYer. Until next time, stay safe, stay cool, and keep that summer breeze going strong! 🌬️❄️
- Samantha, Home Comfort Advisor
