Installing a window air conditioner in a casement window requires a specialized unit or conversion kit designed for vertical, crank-style openings. Standard ACs won’t fit—opt for a low-profile, casement-specific model or use a manufacturer-approved side-mount kit to ensure a secure, weathertight seal and efficient cooling performance.

Key Takeaways

• Measure your window first: Ensure the AC unit fits casement window dimensions precisely.
• Choose a side-discharge unit: Ideal for horizontal sliding or casement windows.
• Secure with mounting brackets: Prevents movement and improves energy efficiency.
• Check for weather sealing: Gaps reduce cooling and increase energy costs.
• Verify electrical requirements: Match voltage and outlet type to avoid hazards.
• Prioritize noise levels: Select quieter models for bedrooms or offices.

Why Casement Windows Need Special Air Conditioning Solutions

Let’s be real—when summer hits, the last thing you want is a sweltering home. But if you live in an older building or a cozy apartment with casement windows, your cooling options feel limited. I’ve been there. My first apartment in Chicago had beautiful, wide casement windows that swung open like a door. They were charming—until I realized standard window AC units just wouldn’t fit. That’s when I discovered the world of window air conditioners for casement windows.

Casement windows are hinged on the side and open outward or inward with a crank. Unlike traditional sliding or double-hung windows, they don’t have a vertical sash to support a standard AC unit. That means you can’t just slide in a typical 24-inch window AC and call it a day. You need a specialized solution. And trust me, the wrong choice can lead to leaks, poor cooling, and even structural damage. But don’t worry—after months of research, trial, and a few (okay, several) mistakes, I’ve learned exactly what works and what doesn’t. In this guide, I’ll walk you through everything you need to know to pick and install the best window air conditioner for casement window setups.

Understanding Casement Windows and Their Cooling Challenges

What Makes Casement Windows Different?

Casement windows are unique. They’re typically taller than they are wide, and they open outward (sometimes inward) using a hand crank. This design is great for ventilation and energy efficiency when closed, but it poses a challenge for air conditioning. Most window ACs rely on the vertical sash of a double-hung window to sit securely. Casement windows don’t have that—so you can’t just plop a standard unit in and expect it to stay put.

For example, my casement window was 32 inches tall and 24 inches wide, with a crank handle that stuck out about 3 inches. A regular 18,000 BTU AC unit was too wide, and even if it fit, there was no way to secure it without blocking the crank or risking it falling out. That’s why you need a casement window air conditioner designed for this specific layout.

Common Installation Problems (And Why They Happen)

• No sash support: Without a sill or sash to rest on, the AC can’t sit level. This leads to poor drainage and potential leaks.
• Crank interference: Many AC units block the window’s crank, making it impossible to open or close the window.
• Air gaps: Poor sealing around the unit allows hot air in and cool air out, reducing efficiency.
• Weight distribution: Without proper bracing, the unit can tilt or fall, especially if it’s heavy or the window frame is old.

I once tried using a universal mounting kit on a standard AC, only to wake up to a puddle on my floor because the unit wasn’t level. Lesson learned: you need a solution built for the job, not a quick fix.

Types of Casement Window ACs: What’s Available?

Thankfully, manufacturers have caught on. There are now several types of air conditioners for casement windows:

• Vertical casement ACs: Tall and narrow, these units fit vertically in casement openings. They often have side brackets or adjustable rails.
• Horizontal slide-out ACs: Designed to slide into a custom frame mounted to the window. The AC itself doesn’t touch the window—it’s supported by the frame.
• Through-the-wall units: Installed directly into the wall, bypassing the window entirely. Best for permanent setups.
• Portable ACs with casement venting kits: Use a flexible hose and a custom adapter to vent out the window. Great for renters.

The key is matching your window’s dimensions, your building’s rules, and your cooling needs to the right type. I went with a vertical casement AC because it was the most secure and didn’t require permanent changes.

How to Choose the Best Window Air Conditioner for Casement Windows

Measure Your Window Accurately (The Right Way)

Before you even look at ACs, measure your window opening. Not the glass—the actual opening where the AC will sit. Use a tape measure to get:

• Height: From the sill (bottom) to the top of the opening. Casement windows are often taller than standard units, so this is critical.

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• Width: At the narrowest point (usually near the crank). Some casement windows taper slightly.
• Depth: How far the window frame extends into the room. This affects how much space the AC will take up inside.
• Crank position: Measure how far the crank sticks out and its location. You’ll need at least 2-3 inches of clearance.

Pro tip: Take three measurements for each dimension (top, middle, bottom) and use the smallest. Windows aren’t always perfectly square. I once bought an AC that was 1/4 inch too tall—it didn’t fit, and I had to return it. Measure twice, buy once.

BTU Size: Don’t Overcool (Or Undercool)

BTU (British Thermal Units) tells you how much cooling power the AC has. But bigger isn’t always better. A unit that’s too large will cool the room quickly, then shut off—leading to a clammy, damp space. One that’s too small will run constantly, wasting energy.

Here’s a quick guide:

• 100–200 sq. ft.: 5,000–6,000 BTU
• 200–300 sq. ft.: 7,000–8,000 BTU
• 300–400 sq. ft.: 9,000–10,000 BTU
• 400–500 sq. ft.: 12,000 BTU

For casement windows, I recommend adding 10% more BTU if the window gets direct sun or if the room is poorly insulated. My south-facing bedroom needed 9,000 BTU instead of 8,000. Also, look for Energy Efficiency Ratio (EER)—aim for 10 or higher. Higher EER means lower energy bills.

Key Features to Look For (Beyond the Basics)

Not all casement ACs are created equal. Here’s what to prioritize:

• Adjustable side rails or brackets: These let you secure the unit to the window frame without drilling. Look for models with rubber padding to protect your window.
• Drainage system: A sloped base or built-in drain pan prevents leaks. My old AC didn’t have this—lesson learned the hard way.
• Remote control & programmable timer: Handy for adjusting settings without getting up. I love setting mine to turn on 30 minutes before I get home.
• Noise level (dB): Under 60 dB is quiet enough for sleeping. I tested a 65 dB unit once—sounded like a hairdryer.
• Washable filter: Easy maintenance means better air quality. I clean mine every two weeks in summer.

One feature I didn’t think I needed but now can’t live without? A sleep mode that gradually adjusts temperature at night. It’s saved me from waking up freezing at 2 AM.

Installation Type: Permanent vs. Removable

Ask yourself: do you want to leave the AC in year-round, or remove it in winter?

• Permanent (through-the-wall or custom frame): More secure, better insulation, but requires drilling. Ideal if you own your home.
• Removable (vertical casement or portable): Easy to take down. Great for renters, but may need resealing each year.

I chose removable for my apartment. I store the AC in the basement during winter and reinstall it in May. It takes 20 minutes, and I don’t have to worry about building approval.

Top 5 Window Air Conditioners for Casement Windows (Real-World Tested)

1. Frigidaire FHWW083WB1 (Best Overall)

This vertical casement AC is a game-changer. At 8,000 BTU, it cooled my 300 sq. ft. bedroom perfectly. The side brackets adjust from 22 to 34 inches wide—perfect for my window. It has a 10.7 EER, so my electric bill barely budged. The remote control is backlit (great for night adjustments), and the noise level is just 52 dB. The only downside? The filter is a bit hard to reach, but I clean it monthly.

Best for: Medium-sized rooms, renters, energy-conscious users.

2. LG LW8016ER (Best for Large Rooms)

Need more power? This 8,000 BTU unit is wider (23.6 inches) but designed for casement frames. It uses dual brackets that attach to the window’s side rails, so it doesn’t block the crank. The inverter technology adjusts cooling speed, saving energy. I tested it in a 400 sq. ft. living room—it kept the space cool even during a 95°F heatwave. The downside: it’s heavy (50 lbs), so you’ll need help lifting it.

Best for: Large rooms, high-heat areas, energy efficiency.

3. Friedrich KCL18A10A (Best Through-the-Wall)

If you’re okay with a permanent install, this 18,000 BTU through-the-wall unit is a beast. It’s designed to fit into a 26.5 x 15.5-inch wall sleeve (sold separately). The slide-out chassis makes maintenance easy. It has a 10.5 EER and a 24-hour timer. I installed it in a sunroom with a casement window—it cooled the space in 15 minutes. The catch? You need a 230V outlet and professional installation.

Best for: Permanent setups, large spaces, sunrooms.

4. Honeywell HL14CESWB (Best Portable for Casement)

Don’t want to install anything? This 14,000 BTU portable AC comes with a casement window venting kit—a custom adapter that seals the hose to your window. I used it in a room with a crank that stuck out too far for a standard AC. It’s heavy (75 lbs), so the included casters are a lifesaver. The downside: it’s louder (65 dB) and uses more energy (9.8 EER).

Best for: Renters, rooms with tricky cranks, temporary solutions.

5. Keystone KSTAW08A (Best Budget)

This 8,000 BTU unit costs under $300 but doesn’t skimp on features. It has side brackets for casement windows, a 10.3 EER, and a 24-hour timer. I tested it in a 250 sq. ft. home office—it kept the space cool without breaking the bank. The remote control is basic, and the noise level is 62 dB, but for the price, it’s a steal.

Best for: Budget buyers, small rooms, occasional use.

Step-by-Step Installation Guide (No Handyman Required)

Tools You’ll Need

• Tape measure
• Level
• Drill (if using brackets)
• Screwdriver
• Silicone sealant (for gaps)
• Helper (for lifting heavy units)

Don’t skip the helper—I tried lifting a 50-lb AC alone and almost dropped it. Not fun.

Installation Steps (Vertical Casement AC)

1. Prepare the window: Open the casement window fully. Clean the sill and frame.
2. Install side brackets: Most casement ACs come with adjustable brackets. Position them on the window frame’s sides, ensuring they don’t block the crank. Use the level to make sure they’re even. Mark drill holes and secure with screws.
3. Set the AC in place: With a helper, lift the AC and slide it onto the brackets. It should sit level—check with the level tool. Adjust the brackets if needed.
4. Seal the gaps: Use foam weatherstripping or silicone sealant around the top and sides to prevent air leaks. I use clear silicone so it’s not visible.
5. Connect power: Plug in the AC and test it. Run it for 10 minutes to check for leaks or strange noises.
6. Secure the crank: If the AC blocks the crank, use a crank extension kit (sold separately) to access it.

Pro tip: Take photos during installation. You’ll need them when you remove the AC later.

Troubleshooting Common Issues

• Unit isn’t level: Adjust the side brackets. A tilted AC won’t drain properly.
• Air leaks: Reapply sealant or add foam tape. I once had a 1-inch gap—my energy bill doubled.
• Crank blocked: Use a crank extension or choose a narrower AC.
• Water leaks: Check the drain pan and slope. My AC leaked because the brackets were loose.

I once forgot to seal the top gap. It rained, and the water dripped down the wall. Never again.

Maintenance, Safety, and Long-Term Care

Cleaning and Filter Care

Dirty filters reduce efficiency and spread dust. Clean your filter every 2–4 weeks in summer:

1. Turn off and unplug the AC.
2. Remove the front panel (usually snaps off).
3. Rinse the filter under water. Let it air dry—never use a dryer.
4. Reinstall and plug in.

I set a phone reminder every month. It takes 5 minutes and keeps my AC running smoothly.

Seasonal Removal and Storage

When winter comes:

1. Drain the AC (if it has a drain plug).
2. Remove it from the window.
3. Clean the unit thoroughly.
4. Store it in a dry place, preferably in its original box.

I store mine in a closet with a dehumidifier nearby to prevent mold.

Safety Tips

• Check electrical cords: Look for fraying or damage. Replace if needed.
• Don’t overload circuits: Use a dedicated outlet. I once blew a fuse because I had a space heater on the same circuit.
• Secure the unit: Ensure brackets are tight. A falling AC is a hazard.
• Inspect annually: Before each season, check for cracks, leaks, or worn parts.

Safety first—my neighbor’s AC fell out of a second-story window because the brackets failed. Scary.

Data Table: Comparison of Top Casement Window ACs

Model	BTU	EER	Dimensions (HxWxD)	Noise (dB)	Price Range	Best For
Frigidaire FHWW083WB1	8,000	10.7	22.5″ x 19.5″ x 20.5″	52	$350–$400	Medium rooms, renters
LG LW8016ER	8,000	10.8	23.6″ x 19.5″ x 20.5″	54	$400–$450	Large rooms, high heat
Friedrich KCL18A10A	18,000	10.5	26.5″ x 15.5″ x 20.5″	58	$600–$700	Permanent setups
Honeywell HL14CESWB	14,000	9.8	30″ x 19″ x 18″	65	$500–$550	Portable, tricky windows
Keystone KSTAW08A	8,000	10.3	22″ x 19″ x 20″	62	$280–$320	Budget buyers

Final Thoughts: Cooling Your Casement Window Home Right

Finding the best window air conditioner for casement window isn’t about picking the biggest or most expensive unit. It’s about matching the right type, size, and features to your unique space. I’ve been through the trial and error—leaks, noise, and even a near-miss with a falling AC. But now, my casement window setup cools my home efficiently, quietly, and safely.

Remember: measure carefully, choose the right BTU, prioritize energy efficiency, and follow installation steps closely. Whether you go with a vertical casement AC, a through-the-wall unit, or a portable option, the key is a snug, secure fit. And don’t forget maintenance—a clean filter and proper storage can add years to your AC’s life.

You don’t need to live in a sweltering space just because you have casement windows. With the right window air conditioner for casement windows, you can enjoy cool, comfortable summers—no matter what your window looks like. Now, if you’ll excuse me, I’m off to set my timer for 4 PM. My room will be perfectly cool by the time I get home.

Frequently Asked Questions

Can I install a regular window air conditioner in a casement window?

Most standard window AC units aren’t designed for casement windows, which open horizontally with a crank mechanism. You’ll need a specialized window air conditioner for casement window installation or a custom mounting solution to fit the vertical opening.

What type of AC unit works best for casement windows?

Through-the-wall air conditioners or casement-specific models with adjustable side panels are ideal. Look for units with a compact height-to-width ratio to match the narrow vertical opening of crank-out windows.

Do I need special brackets for casement window AC installation?

Yes, most casement window installations require L-brackets or support arms that anchor to the wall or window frame. These prevent the unit from slipping and provide stability since traditional window sill support isn’t possible.

How do I seal a window air conditioner for casement window gaps?

Use foam weatherstripping or custom plexiglass side panels to cover gaps between the unit and window frame. Proper sealing prevents hot air leaks and improves cooling efficiency.

Can I use a portable AC instead of a casement window unit?

Yes, portable ACs with casement window venting kits are a viable alternative. However, they’re generally less efficient than fixed units and require a hose permanently routed through the window.

What’s the maximum BTU for a casement window air conditioner?

Most casement window units range from 5,000 to 10,000 BTUs due to size constraints. Choose based on room size—5,000 BTUs for 150 sq ft, up to 10,000 BTUs for 450 sq ft—for optimal cooling.