Keystone KSTHW18B 18,800 BTU Window AC with Heat Review: 230V
A 230V window air conditioner with 18,800 BTU cooling and 16,000 BTU supplemental heat for spaces up to 1,000 sq. ft. Includes a temperature-sensing remote, Energy Saver and Sleep modes and a 24-hour timer.
By Daniel Brooks
Updated October 8, 2026
The Keystone KSTHW18B 18,800 BTU Window Air Conditioner with Heat is a 230V unit that combines 18,800 BTU of cooling with 16,000 BTU of supplemental heat for large spaces up to 1,000 square feet. It also dehumidifies and circulates air. Among large conventional window air conditioners, it is aimed at buyers who want one window unit for summer cooling and cool-weather warmth.
Keystone is clear that it needs a special 230-volt, 25-amp outlet and that the heat mode is supplemental, not a primary heat source. We evaluated it based on the manufacturer’s specifications.
Our Verdict
This Keystone is a capable heat and cool combo for big rooms. Its strongest points are 18,800 BTU of cooling, 16,000 BTU of supplemental heat, a temperature-sensing remote that Keystone calls I Sense or Follow Me, Energy Saver and Sleep modes, a programmable 24-hour timer and a warranty that adds 4 extra years on the sealed system. The listed noise level is 55 dB.
The trade-offs are significant. It weighs 117.3 pounds, needs a 230V 25-amp outlet and a window at least 28 inches wide and 18.5 inches high, and its heat only works with outdoor temperatures between 23 and 76 degrees. It holds 3.8 stars from 69 ratings. If you have the right circuit and a large room, it is worth considering.
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Key Specifications
| Feature | Specification |
|---|---|
| Brand | Keystone |
| Model | KSTHW18B |
| Type | Window air conditioner with supplemental heat |
| Cooling Capacity | 18,800 BTU |
| Heating Capacity | 16,000 BTU supplemental |
| Room Size (listed) | Up to 1,000 sq. ft. |
| Efficiency | 10.7 (listed as SEER) |
| Noise Level | 55 dB |
| Voltage / Power | 230V, 25-amp outlet, 4800W |
| Window Fit | 28″ to 40.5″ wide, 18.5″ minimum height |
| Dimensions | 25.39″D x 23.62″W x 17.91″H |
| Weight | 117.3 pounds |
| Modes | Cool, Supplemental Heat, Dehumidify, Fan, Energy Saver, Sleep |
| Remote | Temperature-sensing LCD remote |
| Timer | Programmable 24-hour |
| Compressor | Scroll, no inverter |
| Refrigerant | R-32 |
| Warranty | 1 year parts and labor, plus 4 additional years on the sealed system |
Cooling Capacity and Room Size
Keystone rates the KSTHW18B at 18,800 BTU for large spaces up to 1,000 square feet, such as living rooms and apartments. That covers a large open-plan area, a finished basement or a big family room.
Make sure your space needs this capacity. In a room well under 700 square feet, an 18,800 BTU unit will cool quickly and cycle off before removing much humidity. The dehumidify mode helps, but matching the unit to the room matters more.
ENERGY STAR publishes this general guide for sizing a room air conditioner by floor area:
| Room Size (sq ft) | Cooling Capacity (BTU/hr) |
|---|---|
| 100 to 150 | 5,000 |
| 150 to 250 | 6,000 |
| 250 to 300 | 7,000 |
| 300 to 350 | 8,000 |
| 350 to 400 | 9,000 |
| 400 to 450 | 10,000 |
| 450 to 550 | 12,000 |
| 550 to 700 | 14,000 |
| 700 to 1,000 | 18,000 |
Adjust for your room: reduce capacity by 10 percent for a heavily shaded room, increase it by 10 percent for a very sunny room, add 600 BTU for each regular occupant beyond two, and add 4,000 BTU if the unit cools a kitchen. Source: ENERGY STAR.
At its listed 18,800 BTU, it is slightly above the chart’s 18,000 BTU row for 700 to 1,000 square feet, which matches Keystone’s coverage claim.
Installation and Fit
The listed window opening is 28 to 40.5 inches wide with a minimum height of 18.5 inches. A window installation kit, the remote, batteries and a mesh air filter are included.
The cabinet measures 25.39 inches deep, 23.62 inches wide and 17.91 inches tall, and weighs 117.3 pounds. That is a job for at least two strong people, and a professional installer is worth considering. Follow the manual for support brackets. Keystone states the unit needs a special 230-volt, 25-amp outlet and will not work on standard 115V household outlets. Never use an adapter or extension cord; have an electrician install or confirm the circuit.
Noise, Energy Use and Efficiency
The listed noise level is 55 dB, which is moderate for a unit of this size. In a large living area with normal activity, it should not be intrusive.
The listing gives an efficiency figure of 10.7, labeled as SEER, and a power draw of 4800 watts, which likely reflects the heater. Energy Saver and Sleep modes help reduce consumption, and the programmable 24-hour timer limits running time. The compressor has no inverter.
Controls and Smart Features
The temperature-sensing remote is the standout. It measures the temperature where you are, shows it on its LCD screen and sends the reading to the unit every 3 minutes. In a large room, that helps the AC respond to conditions at your seat instead of near the window.
You also get Energy Saver and Sleep modes, a 24-hour timer and modes for cooling, supplemental heating, dehumidifying and fan circulation. There is no Wi-Fi or app control.
The supplemental heat works when outdoor temperatures are between 23 and 76 degrees Fahrenheit. Keystone states it is meant to complement a primary heat source, so use it for spring and fall rather than as your only winter heat.
Maintenance and Drainage
The washable mesh air filter is easy to clean. Because the unit can run for heating as well as cooling, check the filter regularly through the year.
The listing does not describe condensate drainage, so check the manual for how water is handled in cooling, dehumidify and heat modes. The warranty is a strong point: 1 year parts and labor, plus 4 additional years on the sealed system.
Pros and Cons
| Pros | Cons |
|---|---|
| 18,800 BTU cooling plus 16,000 BTU heat | Requires a 230V 25-amp outlet |
| Temperature-sensing LCD remote | Very heavy at 117.3 pounds |
| Energy Saver, Sleep and 24-hour timer | Heat only for outdoor temps of 23 to 76 degrees |
| Extra 4 years of sealed system coverage | Needs a window at least 28″ wide and 18.5″ high |
| Listed noise level of 55 dB | No Wi-Fi or app control |
Who Should Buy It
| Who Should Buy It? | Who Should Look Elsewhere? |
|---|---|
| Large rooms of 700 to 1,000 sq. ft. | Homes with only standard outlets |
| Homes with a 230V circuit near the window | Anyone needing a primary winter heater |
| Buyers wanting cooling and mild-weather heat | Anyone without help for a 117.3 pound install |
| Buyers who want room-temperature sensing | Smart home users wanting app control |
| Buyers who value a longer sealed system warranty | Windows under 18.5″ of opening height |
Final Verdict
The Keystone KSTHW18B 18,800 BTU Window Air Conditioner with Heat combines strong cooling, 16,000 BTU of supplemental heat, a temperature-sensing remote and an extended sealed system warranty for large spaces up to 1,000 square feet. The compromises are a 230V 25-amp requirement, a 117.3 pound weight and a heat mode limited to milder outdoor temperatures. You can check the current price and details for the Keystone KSTHW18B 18,800 BTU Window Air Conditioner with Heat, or compare other window air conditioners with heat.
Frequently Asked Questions
What outlet does the Keystone KSTHW18B need?
Keystone states it needs a special 230-volt, 25-amp outlet and does not work with standard 115V household outlets.
Can it heat my home in winter?
Its 16,000 BTU heat is supplemental and works when outdoor temperatures are between 23 and 76 degrees. Keystone says it should not be your only heat source.
How does the remote sense temperature?
The remote measures the temperature where you are, displays it on its LCD screen and sends the reading to the unit every 3 minutes.
What warranty does it have?
Keystone lists 1 year parts and labor, plus an additional 4 years for the sealed system.
About the author
Daniel Brooks is a home cooling editor at WikiCooling, covering window, portable, through-the-wall and mini-split air conditioners, fans, and dehumidifiers. He researches cooling capacity, energy efficiency, noise levels, installation requirements, and buyer feedback to help homeowners choose the right unit for their room size, climate, and budget.