In this blog:
Explore how to choose a more energy-efficient window AC unit by learning how different ratings, sizing and home features can affect cooling performance.
- Find out why you should consider features like BTU sizing, CEER ratings, ENERGY STARⓇ certifications, inverter compressors and refrigerants when choosing a unit.
- See how room size, sunlight, occupancy and other factors can determine the cooling capacity your AC unit needs.
- Understand how energy-efficient windows can reduce heat gain and air leakage, helping your AC unit work more efficiently in your Colorado home.
Today’s window air conditioning units are a far cry from the bulky, power-guzzling designs of the past. Besides being sleeker and more cost-effective, most are also much more energy-efficient. For Colorado homeowners who want effective cooling without spiking their energy bills, such added sustainability can quite literally pay off. ENERGY STAR estimates that a certified unit uses 9% less energy than standard models. They also cost less than $70 per year to run, on average.
Upgrading to an energy-efficient window AC unit can help you create a more comfortable living space without breaking the bank. However, you have to make sure that you’re choosing a unit that’s the right fit for the space. Here’s a closer look at the different factors that can guide your decision.
What Is an Energy-Efficient Window AC Unit?
A window AC unit is a compact, self-contained, electricity-powered cooling system that’s perfect for spaces where central air conditioning isn’t feasible, such as apartments, small homes or single rooms. Once fitted into your window, the unit will work to cool the air inside a given space and expel the warmer air outside. An energy-efficient window unit is designed to perform this process without using as much power as other models.
Modern window units come in sizes that will fit most standard windows, with options also available for custom windows. They’re also designed to be quite user-friendly, adapting to your changing needs and routines.
Built-in unit features can include:
- Adjustable thermostats
- Remote controls
- Timers
- Multi-speed fans
- Smartphone controls
- Built-in air purifiers and dehumidifiers
- Noise reduction technology
- Energy-saver modes
Because all window units are different, you’ll want to compare your options before deciding on the product that’s right for your home. If you’re prioritizing energy efficiency in your search, there are a number of factors to keep an eye out for.
What To Look For in Energy-Efficient Window AC Models
As you shop for an energy-efficient window unit, you’re likely to encounter a lot of different terminology and performance data. Here’s a few you can use to compare your options.
BTU Sizing
A window unit’s BTU (British Thermal Units) sizing measures how much heat AC units can remove from a room in a given hour. Smaller rooms typically need window units with lower BTUs, while larger spaces need higher. You can find out more about the recommended BTU for your space in our chart below.
CEER Ratings
Combined Energy Efficiency Ratios (CEERs) measure a unit’s efficiency by weighing how much power the unit consumes while running and when idling in standby mode. CEERs are measured in a range of 8 to 15. Generally speaking, a good CEER is 12.0 or more. A new U.S. Department of Energy (DOE) rule also recently came into effect which increases the minimum CEER ratings required in newly manufactured units.
ENERGY STAR Ratings
The ENERGY STAR program, run by the U.S. Environmental Protection Agency (EPA), recognizes energy-efficient products that meet certain performance standards. Most window units that qualify for an ENERGY STAR rating must have a CEER rating of about 12.0 or higher.
Inverter Compressors
Older window units had fixed-speed air compressors, which ran at a constant speed while cycling on and off at full power. Many newer, more energy-efficient models contain inverter compressors, which run constantly and automatically adjust in the background to keep temperatures consistent. Doing so keeps spaces more comfortable while reducing the energy waste caused by constant full-power cycling. Although all units vary, inverter compressors may be able to reduce your unit’s energy use by 20–40%.
Refrigerant Types
Window units may also incorporate a variety of refrigerants, and some are more energy-efficient and eco-friendly than others. A few good examples are:
- R-32
- R-454B
- R-290 (Propane)
Each of these refrigerants also has a different Global Warming Potential (GWP) ratings that you might want to consider when making your choice. The lower the GWP, the lower the environmental impact when the refrigerant is released.
Window AC Sizing Chart by Room Size and BTU
Your window unit needs to provide appropriate cooling capacity to effectively cool your room. If it’s not powerful enough, the unit may fail to perform optimally, waste energy and create more discomfort in your space. To choose the right fit, compare a window unit’s BTU capacity with the size of the room in question. The chart below shows you how:1
| Room Size (sq. ft.) | Recommended BTU |
| 100–150 | 5,000 BTU |
| 150–250 | 6,000 BTU |
| 250–300 | 7,000 BTU |
| 300–350 | 8,000 BTU |
| 350–400 | 9,000 BTU |
| 400–450 | 10,000 BTU |
| 450–550 | 12,000 BTU |
| 550–700 | 14,000 BTU |
| 700–1,000 | 18,000 BTU |
| 1,000–1,200 | 21,000 BTU |
| 1,200–1,400 | 23,000 BTU |
| 1,400–1,500 | 24,000 BTU |
1 Source: ENERGY STAR
ENERGY STAR also notes that multiple factors besides a room’s size can affect how much cooling capacity a window unit needs. For example:
- In shaded rooms, lower the capacity by 10%.
- In sunny rooms, increase the capacity by 10%
- In kitchens, increase your capacity by approximately 4,000 BTUs.
- If more than one person plans to occupy a room regularly, add 600 BTUs per additional person.
Is It Cheaper To Run Central AC or a Window Unit?
Broadly speaking, window AC units are more affordable to run than central air conditioners. However, it’s not necessarily a one-to-one comparison, and window units may not be the most efficient choice for every home. The table below compares window units vs. central AC in different scenarios.
| Scenario | Window AC Unit | Central Air |
| Single-room cooling | More cost-effective | Higher costs |
| Whole-home cooling | Inefficient | Very efficient |
| Installation cost | Low | High |
| Long-term energy performance | Depends on unit and insulation | More consistent |
It’s also very important to remember that your Colorado home’s overall energy efficiency is not determined solely by the type of air conditioning unit you have. Other factors, such as insulation and the quality of your home’s windows themselves, can impact the efficiency of your cooling systems.
How Windows Impact AC Efficiency
Your home’s windows are major barriers against the elements, and if they don’t function properly, they will make your home less energy efficient. Drafty, single-pane windows cause air leakage, letting your cooled air escape through small cracks in the frame. They can also allow harmful, unfiltered UV and infrared light to pour into your spaces. These make it harder for any AC system to keep your space comfortable.
By investing in more energy-efficient windows, your home benefits from reduced drafts, lower heat gain and lessened strain on your cooling units. Your systems won’t have to work overtime to cool your home, and your energy consumption will lessen.
What Makes Windows More Energy Efficient?
Modern windows provide much more insulation, heat control and sun protection than their older counterparts. They’re usually engineered with multiple features that help them improve your home’s energy efficiency from the day they’re first installed. Here’s just a few of the features that help Window World’s ENERGY STAR-certified windows perform at their best:
- Weatherstripping: As a first line of defense against the elements, weatherstripping stops moisture and uncomfortable temperatures from entering your home.
- Low-E glass: Microscopic films on the window glass help reduce UV ray penetration, control heat gain and keep your home more comfortable without affecting brightness.
- Multi-pane designs: Multiple layers of specially treated glass create a stronger barrier against drafts and incoming heat.
- Argon gas inserts: Ultra-thin gas layers between panes help add extra insulation.
- Warm-edge spacers: Exterior edges of a frame unit remain tightly sealed against heat gain or air loss.
- Multichamber vinyl framing: The intricate interior of your frames traps or repels outdoor moisture and bad air.
- Insulated foam cores: Window frames contain durable foam insulation that serve as extra protection against changing temperatures.
Cooling Your Colorado Home Efficiently
Colorado’s unique climate and landscape create a few extra considerations for homeowners looking for energy-efficient AC units. For example:
- Colorado’s climate can be dry and semi-arid in places, so you’ll want to consider how much dehumidification your unit should provide. Most window units dehumidify air to an extent, but you may not need a unit that provides any special protection.
- High-elevation Colorado homes naturally receive more sun exposure thanks to the thinner atmosphere. This increases the risk of heat gain throughout your home. To ensure your window units provide appropriate cooling, you may need to apply the 10% sunny-room BTU increase recommended by ENERGY STAR.
Keep in mind, however, that every home and every room are unique. The window unit you choose will ultimately need to be the best fit for the room in question.
Efficient AC Units Create More Comfortable Homes
Energy-efficient window units can cool your Colorado home without putting a massive dent in your wallet. You’ll just need to make sure you have the right unit in place. Considering factors like the size of the room, the BTU power your unit supplies and various energy efficiency features will help you make your choice.
Still, the unit is only part of the challenge. You’ll also need windows that don’t add to your unit’s cooling burden. If you’re noticing drafts, damaged frames or even moisture between panes, it’s all a sign that it’s time to upgrade to more energy-efficient windows. Window World of Denver can help.
Schedule a free in-home evaluation today.
Frequently Asked Questions
Is a window AC unit more energy-efficient than central air?
AC units may be more efficient than central air in some ways and not in others. It is not typically better at efficient whole-home cooling. To compare the two options further, refer to our chart above.
What size window AC unit do I need?
In terms of physical size, most window AC units are designed to fit most standard-sized windows. Measure your window’s height, length and width to confirm the right dimensions.
Additionally, make sure you choose a window unit that is powerful enough to cool a space efficiently. You can gauge this by checking if your unit’s BTU rating is the right fit for the size of the space. ENERGY STAR’s Room Size vs. Recommended BTU chart, which we’ve included above, can help you decide.
How much electricity does a window AC save per month?
Your window unit’s electricity savings depend on a lot of different factors, including:
- How often you use the unit
- What temperature you run the unit on (colder typically means more power used)
- Local electricity rates
- The energy efficiency of the unit itself
It’s also important to remember that your window unit is just one factor that contributes to your home’s energy use. If your home is full of drafts and bad insulation, you may force your unit to work overtime, driving costs up.
Can new windows reduce my AC usage?
Yes, they can. Most new window designs are much more energy efficient than older models. They may include a variety of design features that help block drafts, weather intrusion and heat gain that put extra strain on any cooling unit. If you have windows that balance light and provide proper insulation, you’ll create more balanced indoor temperatures, and your AC unit won’t have to work as hard.
Do I need to replace my window AC because of the new 2026 efficiency rule?
No, you do not. The new DOE energy efficiency rule requires newly manufactured window units to meet certain minimum CEER standards, which help improve their energy efficiency. They have no effect on units that are already installed.