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.
Example 1: 1960s Ranch with Casement Windows — The Petersons' ranch home has casement windows throughout. They installed a Soleus Air 8,000 BTU in the living room casement window (18" wide opening). The vertical installation took 45 minutes and cools their 320 sq ft room effectively.
Example 2: Condo with Horizontal Sliding Windows — Kim's condo has sliding windows that open horizontally. She installed a Frigidaire 8,000 BTU casement AC in the left panel opening. The unit's vertical profile fits the narrow opening, and the fill panel seals the remaining space above.
Example 3: Choosing Between Casement AC and Portable — Diego compared a Koldfront casement AC ($470) vs. a portable AC ($380) for his bedroom with awning windows. The casement AC won on efficiency (CEER 10.5 vs. 8.5), noise (50 dB vs. 53 dB), and floor space (none vs. 2.5 sq ft). The portable was only cheaper upfront.
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 |
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.