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.

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.

Window unitENERGY STAR

Keystone · Model KSTAW121WA

12,000 BTU Inverter Window Air Conditioner

Name: Keystone 12,000 BTU Inverter Window Air Conditioner
Brand: Keystone
Price: 449.99 USD
Availability: InStock

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 Sylvane

Price checked Oct 1, 2026

Buy at Sylvane In stock

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Will it cool your room?

Room size (assumed)550 sq ft ≈ 51.1 m²

Fits a 51.1 m² room

This unit's cooling matches a 550 sq ft room. Set your room size to check the fit for your space.

Running costest.

~$110/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.

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.

Cooling

3.5 kW

Size

Average

Noise

54 dB

Audible

Install: Self-fit, no pro neededPermission: Usually no permit

Performance

Cooling capacity: 12,000 BTU · 3.5 kW
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
Warranty: 1-Year Parts & Laabor

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.

Installation

Self-fit, no pro needed

Refrigerant

R-32

GeneralRenters: get written landlord consent firstReviewed June 2026Often blocks install

GeneralCondo / HOA: exterior changes need approvalReviewed June 2026Permit required

GeneralHistoric / listed buildings: consent before any exterior unitReviewed June 2026Permit required

MassachusettsMassachusetts: local historic district approval (MGL c.40C)Reviewed June 2026Permit required

United StatesUS: local mechanical and electrical permits (vary by city)Reviewed June 2026Permit required

See full rules by region

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.
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.