The best air conditioner for casement and sliding windows in 2026 is the Soleus Air Exclusive Series (8,000 BTU, CEER 11.5, 47 dB), priced at approximately $420. Casement/vertical ACs install in the narrow vertical opening of casement (crank-out) and sliding windows that can't fit standard horizontal window units.
Standard window ACs require a double-hung window with a horizontal sill. If your home has casement, sliding, awning, or other non-standard windows, this guide covers every AC option that actually works.
Which Windows Need a Casement/Vertical AC?
| Window Type | Why Standard ACs Don't Fit | Casement AC Works? |
|---|---|---|
| Casement (crank-out) | Window swings outward; no horizontal sill | Yes |
| Horizontal sliding | Opens side-to-side, not up-and-down | Yes |
| Awning (top-hinged) | Opens outward from top | Depends on dimensions |
| Hopper (bottom-hinged) | Opens inward from bottom | Depends on dimensions |
| Jalousie (louvered) | Overlapping glass slats | Usually no |
Top Casement/Vertical ACs Ranked
| Rank | Model | BTU | CEER | Noise (Low) | Window Width Min | Price |
|---|---|---|---|---|---|---|
| 1 | Soleus Air Exclusive Series | 8,000 | 11.5 | 47 dB | 15" | $420 |
| 2 | LG LP0823GSSM (casement kit) | 8,000 | 10.8 | 48 dB | 15" | $450 |
| 3 | Frigidaire FHWC084WB1 | 8,000 | 11.2 | 48 dB | 15.5" | $400 |
| 4 | Koldfront CAC8000W | 8,000 | 10.5 | 50 dB | 14.5" | $470 |
| 5 | Soleus Air Exclusive 10K | 10,000 | 10.8 | 49 dB | 16" | $500 |
| 6 | Frigidaire FHWC104WB1 | 10,000 | 10.5 | 50 dB | 16" | $470 |
| 7 | Keystone KSTAW10CE | 10,000 | 10.2 | 51 dB | 15.5" | $430 |
Installation Dimensions
| Model | Unit Width | Unit Height | Unit Depth | Min Window Opening |
|---|---|---|---|---|
| Soleus Air 8K | 14.5" | 20.3" | 26" | 15" W × 21" H |
| LG LP0823GSSM | 14.8" | 20" | 25" | 15" W × 20.5" H |
| Frigidaire FHWC084WB1 | 15" | 20.5" | 25.5" | 15.5" W × 21" H |
| Koldfront CAC8000W | 14" | 20.3" | 25" | 14.5" W × 21" H |
How Casement ACs Install
Unlike standard horizontal window ACs, casement/vertical units install vertically with the compressor and condenser positioned at one end (either top or bottom, depending on the model).
Installation Steps
- Open the casement or sliding window fully
- Attach the mounting bracket to the window frame
- Insert the AC unit vertically into the bracket with the outdoor section facing outside
- Extend the fill panels to seal the remaining opening
- Secure with screws and seal gaps with included weatherstrip
The fill panels are typically taller and narrower than standard accordion panels, designed to fill the vertical window opening above and/or below the AC unit.
Casement ACs are heavier relative to their BTU output compared to standard window ACs because the vertical form factor concentrates weight in a narrow area. Most 8,000 BTU casement units weigh 55–70 lbs. Use the mounting bracket — don't try to balance the unit on a narrow sill.
Casement AC vs. Portable AC vs. Through-the-Wall
| Factor | Casement/Vertical AC | Portable AC | Through-the-Wall |
|---|---|---|---|
| Price | $400–$500 | $280–$500 | $650–$1,500 |
| Efficiency (CEER) | 10.2–11.5 | 8.0–10.5 | 10.0–11.3 |
| Noise | 47–51 dB | 48–56 dB | 43–48 dB |
| Floor Space | None | 2–4 sq ft | None |
| Window Type | Casement, sliding | Any | No window needed |
| Installation | DIY (45–60 min) | DIY (10 min) | Professional |
| Structural Modification | None | None | Wall hole |
Sliding-Window Installation Detail
Horizontal sliding windows differ from casement (crank-out) windows in ways that change the install sequence. A slider splits into a fixed panel and a sliding panel, with the sliding sash moving along horizontal tracks. When a casement/vertical AC goes into a slider, the AC sits against the fixed panel's edge and fills the opening created by moving the sliding panel out of the way.
Steps that diverge from a standard casement install:
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Open the sliding sash fully. The opening width equals the width of the sliding panel — typically half the total window width, not the full frame width. Verify the AC will fit in that reduced opening before starting.
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Add a filler strip along the top track if AC height is less than window opening. Casement AC units are tall, but some sliders are taller still. A wood or vinyl strip along the top of the sliding-panel track closes the vertical gap.
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Install a horizontal locking bar across the sliding-sash groove above the AC. A partially-open horizontal slider with an AC filling the bottom is easier to defeat than a closed double-hung with a top-sash lock. A dowel or aftermarket track bar cut to length prevents the sliding sash from being reopened from outside.
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Weatherstrip the closing edge where the sliding sash meets the AC's side frame. This joint is often the largest air-leak path in a slider install.
For very wide sliding windows — 5 feet or wider — a single casement AC leaves a large unfilled gap even with fully-extended fill panels. In those cases, cutting a rigid plexiglass or exterior-grade plywood infill panel to fill the excess opening is the durable fix. Foam accordion panels flex, sag, and leak air when spanning that much distance.
Weight, Bracket Sizing, and Upper-Floor Installs
Casement AC units in the 8,000 BTU class typically weigh 55–70 lb, concentrated in a narrow vertical footprint. Because the base contact area is smaller than a horizontal window AC of the same weight, load per linear inch of sill contact is higher. On older wood sills with any softening or rot, that concentrated load matters more than the total weight.
Before installing, probe the sill with an awl or narrow screwdriver. If the tool sinks into the wood without much resistance, the sill is compromised and needs repair before it holds a 60-pound unit for a full cooling season.
Bracket requirements scale with weight and floor height. Any casement AC over roughly 60 lb installed on the third floor or higher should use a support bracket regardless of local code. In New York City, Local Law 30 of 2004 requires a support bracket for through-the-window ACs installed above the ground floor, and casement units are not exempt.
Casement bracket kits are less standardized than horizontal-unit brackets. Verify the bracket is rated for the specific unit's weight and dimensions before buying — a bracket sized for a horizontal AC will not necessarily hold a vertical one securely.
One common install error: casement ACs often end up on the interior side of the fixed panel, with only the outdoor half projecting into the opening. That geometry leaves the weather-sealing surface on the wrong side of the wall plane, and rain runs into the interior joint. The correct orientation on most models puts the outdoor half through the opening past the wall plane, with the fixed weatherstrip on the outside face of the sash.
Key Takeaways
- Casement ACs fit casement, sliding, and narrow windows that can't accommodate standard horizontal units.
- Soleus Air leads the category with the best CEER (11.5) and widest model selection.
- BTU range is limited to 8,000–12,000 — fewer options than standard window ACs.
- Casement ACs are more efficient and quieter than portable ACs — choose casement over portable whenever possible.
- Minimum window width is typically 14.5"–16" — measure your opening before purchasing.
- Installation is DIY but takes 45–60 minutes — longer than standard window ACs due to vertical mounting.
Frequently Asked Questions
Not directly. Standard window ACs are designed for double-hung windows that open vertically. For horizontal sliding windows, you need a casement/vertical AC or a portable AC with a sliding window adapter kit. Some people create DIY plexiglass adapter panels, but this is less secure and less well-sealed than a purpose-built casement AC.