Pros / This window AC unit has the lowest estimated energy cost of any product we reviewed.

Cons / This unit does not provide four-way directional airflow.

 Verdict / This compact Keystone AC unit KSTAW05B is an efficient and compact solution for smaller rooms.

The Keystone KSTAW05B is a small window ac unit with several standout features. This product comes with a variety of settings, including an energy-saving mode, three cooling speeds and three fan speeds. Its design is compact, but the unit still provides enough power to cool up to 150 square feet. Furthermore, it is an Energy Star qualified device that, when comparing its estimated annual energy costs, has the lowest operating cost of any product on our lineup.

If you are looking for a mini window air conditioner, this Keystone AC unit’s performance is ideal. It provides up to 5,000 British thermal units (Btu). A British thermal units is the amount of energy needed to cool or heat one pound of water by one degree Fahrenheit. The higher the number of Btu, the more space the unit can cool. The Keystone KSTAW05B, with its 5,000 Btu, can cool up to 150 square feet.

There are several setting options to choose from to ensure the unit helps you feel comfortable in your home. The device features three different cooling speeds. In these cooling modes, the fan and the compressor work together to bring down the temperature of the room. If you choose one of the three fan settings on the device instead, only the fan runs to circulate and move air around the room. However, it does not feature four-way directional airflow, which allows you to direct the flow of air to the area you want it the most.

There are several additional modes included on this device that provide you with other options when choosing the right temperature for your room. A sleep mode is featured on the device, and this gradually increases the temperature while you sleep. Additionally, an energy saving mode helps cut energy costs. It also has an auto-restart tool, which automatically saves and resumes your settings if the product’s power is interrupted. You do not need to worry about this window AC taking up too much space in your home. It is only 12 inches tall, 16 inches wide and 15.75 inches long. It also weighs only 40 pounds, making it the lightest air conditioner in our comparison.

It is an Energy Star qualified device and has an energy efficiency rating (EER) of 11.2. Anything over 10 is respectable but there were units that got higher numbers. When we estimated the energy cost of this device, it was only $38.53. This cost is based on the room air conditioner running eight hours a day for a three-month period. Many similar products, such as the Frigidaire FFRE0633Q1, cost $7 to $24 more to run each year. The warranty on this device is quite good when you compare it to other window AC units. It features a one-year appliance warranty and five-year warranty on the compressor.

Keystone KSTAW05B Visit Site
  • Energy Efficiency Ratio
  • Maximum Air Flow
  • Compressor Warranty
  1. Based on the industry standard of Btu divided by watts used.
    More is better.
  2. 7  Keystone KSTAW05B
    11.2 Cubic Feet per Minute
  3. 11.2 Cubic Feet per Minute
  4. 12.1 Cubic Feet per Minute
  5. 11.3 Cubic Feet per Minute
  6. Category Average
    11.12 Cubic Feet per Minute


The Keystone KSTAW05B has features and options to ensure you enjoy a cool and comfortable summer. The variety of settings and modes, as well as its lower annual energy costs and small design, all benefit this model. Still, it does lack some features like directional airflow. If saving money on your utilities and conserving energy are your main goals, the Keystone KSTAW05B is a good option to consider.

Keystone KSTAW05B Visit Site

Specifications and Benchmarks


Room Size (square feet)
Estimated Annual Energy Cost
Maximum Window Kit Width (inches)
Minimum Window Height (inches)


Energy Efficiency Ratio (EER)
Maximum Air Flow (CFM)
Moisture Removal (pints/hour)
Energy Star Qualified
3 Fan Speeds
AHAM Certified
UL Listed
Chlorine-Free Refrigerant
Not Specified


Remote Control
Programmable Timer
Auto Mode
Fan Only
Dehumidify Only
Sleep Mode
Energy Saver Mode
Auto Restart


Air Filter
4-Way Directional Louvers
Noise Level (dB)
Weight (pounds)
Height (inches)
Width (inches)
Depth (inches)
15 3/4

Help & Support

Appliance Warranty
1 Year
Compressor Warranty
5 Years
Email & Telephone
Live Chat