Model
Keystone KSTAW121WA
Rank #231 means 230 of the 404 room air conditioner models we track cost less to run each year; the 43rd efficiency percentile means it uses less energy for its size than 43% of those models.
What does the Keystone KSTAW121WA cost to run per year?
Among the 404 room air conditioner models we track, the Keystone KSTAW121WA's $111/yr running cost ranks it #231, close to dead center. It uses 38% less energy than the U.S. federal standard model in its class, which would cost about $180/yr to run, a saving of roughly $69 a year. Size-adjusted, this model sits close to the class median on efficiency, ahead of 43% of room air conditioner models we track. Its CEER of 15 reflects combined energy efficiency ratio, one of the class's core efficiency levers.
Immediately around it on the leaderboard, the Keplerx KARC12RSVE1 at $111/yr runs a little cheaper and the Keystone KSTAW12INV at $111/yr runs a little more, a sense of how tightly models are packed at this point in the ranking. A room air conditioner typically stays in service for somewhere around 10 years; over that span, the Keystone KSTAW121WA's $111/yr adds up to roughly $1110 in electricity alone, before purchase price or repairs.
Also sold as: Black+Decker BD12NWES.
By the numbers
The Keystone KSTAW121WA normalized against its whole class, so each figure means something.
What it costs you over time
Running cost is an every-year number, so it compounds. At $111/yr, here is what the Keystone KSTAW121WA adds up to before purchase price, water, or repairs enter the math.
Left running for a decade at today's US average rate, the Keystone KSTAW121WA costs about $1110. That is roughly $690 less than a standard model in its class, which would run closer to $1800 over the same ten years.
How the Keystone KSTAW121WA compares
The room air conditioner class we track runs from $51 to $389 a year. At $111/yr, it runs about $12 a year above the class median of $99, and it is about $60 a year more than the cheapest room air conditioner to run at $51. Against the US federal standard model for its class at about $180/yr, the Keystone KSTAW121WA uses 38% less energy.
What drives its running cost
At 12000 BTU/hr, the Keystone KSTAW121WA is a mid-size room air conditioner for its class, which spans 5000 to 34100 BTU/hr with a median of 10100 BTU/hr, neither the size advantage of a small unit nor the size penalty of a large one applies here, so its running cost is a fairer test of efficiency alone. Its CEER of 15, above the class median of 15, reflects combined energy efficiency ratio: a higher figure means it wrings more useful work out of every kilowatt-hour, so it is the efficiency lever to weigh against raw size.
- Combined Energy Efficiency Ratio (CEER). Two units with the same BTU rating can post very different running costs, and CEER is the figure that explains most of that gap.
- BTU cooling capacity. BTU rating scales with room size, and it is usually the first driver of an air conditioner's running cost, ahead of its CEER figure.
- Thermostat and mode usage. How the unit is actually operated, thermostat cycling versus a fixed setting, moves real electricity use more than the rated BTU or CEER figure alone.
Common questions
Is the Keystone KSTAW121WA cheap to run?
Roughly, yes. Its $111/yr figure is close to the class median, ranking #231 of 404, neither a bargain nor a splurge on running cost.
How much does the Keystone KSTAW121WA cost per month?
About $9.28 a month, which is the $111 annual estimate spread across twelve months at the US average rate of $0.1856/kWh. Your own bill scales with your local electricity rate and how heavily you use it.
How is this running-cost figure calculated?
The formula is annual kWh times price per kWh: 600 kWh from ENERGY STAR times the US average of $0.1856/kWh comes to about $111 a year. It covers electricity only, not the purchase price, water, or installation.
How efficient is the Keystone KSTAW121WA for its size?
43rd percentile once size is factored in, a fairly typical result for the class.
Cheaper to run in the same class
Source
ES_1055302_KSTAW121WA_11142024120904_80206320View certified room air conditioner listingsENERGY STAR data as of July 2026Keystone and KSTAW121WA are used here for identification only and are not endorsements. Figures are computed by WattWise Labs from public ENERGY STAR data, not measured in our own lab.