Keystone · Model KSTAW121WA
12,000 BTU Inverter Window Air Conditioner
A window air conditioner rated at 12,000 BTU for rooms up to 550 sq ft. It self-installs in a window.
$449.99
Live price at SylvanePrice checked Oct 27, 2026
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Will it cool your room?
This has more cooling than your 150 sq ft room needs. It can short-cycle and leave the air cool but humid.
Estimated from ENERGY STAR's published annual energy use at about 750 hours of cooling a year (the DOE test standard) and the US average electricity price of 18.44¢/kWh (U.S. Energy Information Administration, Electric Power Monthly Table 5.6.A (residential average, May 2026)). A standardized figure for comparison; your real cost depends on how much you run it, your local rate and your climate.
Local rates vary widely (about 15¢/kWh in Florida to 33¢ in California), and hotter regions run their AC more hours, so your real cost differs.
At a glance
Best for renters and rooms where you cannot install a fixed unit.
Performance
- Cooling capacity
- 12,000 BTU · 3.5 kW
- Power while cooling
- 1,150 W (10.3 A at 115 V), about $0.21 an hour
- Heating capacity
- Cooling only
- Room coverage
- up to 550 sq ft
- Energy Star
- Yes
- CEER
- 15
- Annual energy (cooling)
- 600 kWh
Noise, size & features
- Model number
- KSTAW121WA
- Indoor noise
- 54 dB(A)about as loud as a dishwasher
- Outdoor noise
- Not published
- Indoor unit
- 19.17 x 13.46 x 21.97 in
- Outdoor unit
- None
- Refrigerant
- R-32
- Wi-Fi / app
- Not published
- Outdoor unit needed
- No
- Power supply
- 115 V, NEMA 5-15P plug
- Warranty
- 1-Year Parts & Laabor
Supply voltage, plug, cooling power, cooling current, refrigerant and warranty are from Sylvane's published specifications for this exact configuration, checked Oct 18, 2026.
Power while cooling: From the maximum cooling draw its retailer lists for this exact model. An hour's cost is at that draw and the US average electricity price of 18.44¢/kWh (U.S. Energy Information Administration, Electric Power Monthly Table 5.6.A (residential average, May 2026)). The compressor cycles once the room is cool, so most hours cost less.
What is good
- Uses R-32 (GWP 675), the low-GWP class new US residential equipment moved to.
Installation & the rules that apply
This is a window unit. No EPA Section 608 technician is needed: the refrigerant circuit is factory-sealed and never opened. A plug-in window unit needs no permit, so the friction is with your building rather than the government. Many HOAs restrict window units on appearance grounds, though an HOA regulating how you mount one stands on much firmer ground than one banning cooling outright. Landlords can set conditions, and the falling hazard is taken seriously: New York City, for instance, requires window units to be supported by brackets or mounting rails, and many building insurers and HOAs now require a bracket regardless of city.
Self-fit, no pro needed
R-32
Common questions about the Keystone 12,000 BTU Inverter Window Air Conditioner
- How much does the Keystone 12,000 BTU Inverter Window Air Conditioner cost to run per year?
- About $110 a year. Estimated from ENERGY STAR's published annual energy use at about 750 hours of cooling a year (the DOE test standard) and the US average electricity price of 18.44¢/kWh (U.S. Energy Information Administration, Electric Power Monthly Table 5.6.A (residential average, May 2026)). A standardized figure for comparison; your real cost depends on how much you run it, your local rate and your climate.
- How loud is the Keystone 12,000 BTU Inverter Window Air Conditioner?
- 54 dB(A) indoors, about as loud as a dishwasher.
- How energy-efficient is the Keystone 12,000 BTU Inverter Window Air Conditioner?
- Its efficiency rating is CEER 15, and it is ENERGY STAR certified.
- How many watts does the Keystone 12,000 BTU Inverter Window Air Conditioner use?
- It draws 1,150 watts (10.3 amps at 115 V) while cooling at full power, per its retailer's specification for this exact model. At the US average electricity price that is about $0.21 an hour; once the room is cool the compressor cycles, so most hours cost less.
- What size room does the Keystone 12,000 BTU Inverter Window Air Conditioner cool?
- It is rated to cool a room up to 550 sq ft (12,000 BTU · 3.5 kW).
- Do I need a professional to install the Keystone 12,000 BTU Inverter Window Air Conditioner?
- No. It is a window unit you can fit yourself, no professional needed. Usually no permit.
Compare the Keystone 12,000 BTU Inverter Window Air Conditioner head-to-head
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