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

Cons / It doesn’t provide four-way directional airflow.

 Verdict / The Keystone KSTAW05B is an efficient, compact, affordable window air conditioner with good features and a nice warranty. It’s a good option for cooling a room of up to 150 square feet.

The Keystone KSTAW05B is a small window AC unit with several standout features. It has a variety of settings, including an energy-saving mode, three cooling settings and three fan speeds. Even though it is compact, the unit has enough power to cool up to 150 square feet of space. Furthermore, it is Energy Star qualified and has one of the lowest estimated annual energy costs of any window AC we evaluated. The only AC with lower estimated energy costs is the GE AEM05LX, and both units cost about $38 a year to operate.

This Keystone window air conditioner generates up to 5,000 British thermal units (Btu). A British thermal unit is the amount of energy needed to cool or heat 1 pound of water by 1 degree Fahrenheit, and the higher the Btu rating, the more space the unit can cool. With its 5,000 Btu, the KSTAW05B can cool up to 150 square feet.

When you run the AC unit in one of its three cooling modes, the fan and compressor work together to lower the room’s temperature. If you choose one of the three fan settings, only the fan runs to circulate air around the room. However, the Keystone KSTAW05B doesn’t feature four-way directional airflow, which allows you to direct air from the unit to the area in the room you want it the most.

The AC has several additional modes, including a sleep mode that lets the room’s temperature rise gradually while you sleep. That way, your room isn’t too cold when you wake up. Additionally, it includes an energy-saving mode to help you save money on your electric bill. The KSTAW05B also has an auto-restart tool that saves and resumes your settings if the unit’s power supply is interrupted.

This Keystone model measures only 12 x 16 x 15.75 inches, so it is very compact. It also weighs only 40 pounds, making it the lightest air conditioner we reviewed.

The KSTAW05B is Energy Star qualified, with an Energy Efficiency Ratio (EER) of 11.2. Any ratio over 10 is considered respectable, but there are units that score better. Still, many similar products, including the LG LW8017ERSM, cost $20 more to run each year than this Keystone model.

Compared to other window AC units, the Keystone KSTAW05B has a good warranty. It comes with a one-year appliance warranty and a five-year compressor warranty.

The Keystone KSTAW05B is an affordable window AC with a variety of settings and modes, low annual energy costs and a compact design, all of which add to its value. Still, it’s missing features like four-directional airflow. If you want to save money on your utilities and conserve energy, the Keystone KSTAW05B is a good unit to consider for a small room.

Keystone KSTAW05B Visit Site

Specifications and Benchmarks


Maximum Window Kit Width (Inches)
Minimum Window Height (Inches)
Weight (pounds)
Height (inches)
Width (inches)
Depth (inches)
15 3/4


Energy Efficiency Rating (EER)
Maximum Air Flow (CFM)
Moisture Removal (pints/hour)
Energy Star Qualified
AHAM Certified
UL Listed


Dehumdify Only
Sleep Mode
Energy Saver Mode
Auto Restart

Design & Warranty

Room Size (square feet)
Noise Level (dB)
4-Way Directional Louvers
Appliance Warranty
1 Year
Compressor Warranty
5 Years


Estimated Annual Energy Cost