There is a long-standing debate as to whether it is better to sleep with the windows open in the summer or keep your house closed up tightly with the air conditioning running. There is no question that the less your air conditioner runs, the more you’ll save on energy costs. However, turning off your air conditioner at night doesn’t always make sense, and in some situations, it could see your level of comfort drop drastically without much of a noticeable decrease in your energy bills. With this in mind, let’s take a deeper dive into this subject to see when it makes sense to sleep with the windows open and when you’d be better off leaving the AC on.

Estimated Energy Savings from Turning the AC Off at Night

Some people are surprised to learn exactly how much energy an air conditioner actually uses at night. In hotter, more humid climates, around 60% to 65% of the system’s total energy consumption occurs between the hours of noon and midnight. In places where nighttime temperatures are generally cooler, this number can rise as high as 80% or more. It all depends on how well-insulated your home is and how frequently and for how long your AC runs at night.

Depending on these factors, shutting off your AC at night will usually reduce your total cooling costs by somewhere between 20% and 30%. Even if the nighttime temperature is warm enough that your house is warmer when you wake up due to your AC being turned off at night, the system usually won’t need to use that much additional energy to cool the house off again.

Important Factors to Consider

The outdoor temperature and the humidity level are two of the primary factors that will determine whether you’re better off opening your windows or leaving your air conditioning turned on. In hotter, more humid climates, it generally never makes sense to shut off the AC and open the windows. This is partly because outdoor temperatures will usually stay well above the temperature you have your thermostat set to for most of the night.

In this situation, opening your windows will obviously heat up your house since it allows the hot air from outside to get in. Still, the bigger issue is that opening the windows also drastically increases the humidity level inside the home. High humidity not only makes it feel hotter, but it also reduces the efficiency of your AC system. When the humidity level is too high, it forces the air conditioner to work much harder to properly cool the home. In fact, studies have shown that this can result in the air conditioner using over 20% more energy during the day, which can mostly cancel out any potential energy savings from turning the system off at night.

Luckily, the Denver area doesn’t experience anything like the high heat and humidity found in many other parts of the country. Due to the dry climate, you shouldn’t really ever have to worry about humidity having an effect on your AC system except perhaps in the hours immediately after a major thunderstorm. Nonetheless, this still doesn’t mean that opening your windows at night is always the more efficient option throughout the entire summer. Even in July and August, it’s still usually best to keep the windows closed and the AC running to ensure you stay cool and comfortable as you sleep.

On milder days or when the nighttime temperatures will be down into the 70s or below, opening your windows can be a decent option for saving money. Nevertheless, one factor that is important to consider is how well your attic and the rest of the home are insulated. If your attic isn’t well insulated or properly vented, the temperatures inside it can often rise well above 150 degrees. When the sun sets and the temperatures begin to drop, much of this excess heat will be transferred into the rest of the home. In this situation, shutting off your AC can potentially cause the temperature inside the home to rise by 10 degrees or more in a short time.

Installing additional attic vents or fans can help to overcome this issue by ensuring that the excess heat is released instead of being trapped inside the building. As well, you may want to consider programming your thermostat so that the AC doesn’t shut off until around midnight to prevent your home from getting too hot. Still, if you leave the AC on and the windows open, you’ll obviously use more energy during that period than you would if the windows were closed.

Generally speaking, as long as the temperatures don’t stay in the 80s throughout the night, opening your windows is almost always a more cost-effective option than running your AC all night. Even if the outside temperature is still fairly hot when you go to bed, you can always use a fan or two to help keep you cool as you sleep. This is especially effective if you position the fans so that you can get a through draft blowing in the house.

A single fan will use less than 1% of the total energy that your home’s AC system does. In fact, even a highly efficient air conditioner will use more energy in 10 to 15 minutes than a few fans would use if they ran for 24 hours. This means that even using multiple fans in every room of the house won’t do much to cancel out all of the extra energy you saved from shutting the AC off at night.

Another option is to consider using window air conditioners to keep each of your bedrooms cooler at night. Although window AC units generally aren’t as energy efficient as central air conditioners, they will still typically use less energy overall since you’ll only be cooling some rooms instead of the entire home. A large, 10,000 BTU window AC unit should consume somewhere around 900 watts of electricity per hour, and this is much larger than you’d really ever need to cool a bedroom. On the other hand, even a fairly small central AC unit will typically use at least three to five times more electricity.

Expert HVAC Services from Trusted, Local Professionals

At Summit Heating & A/C, we have been providing professional HVAC services to residents of Denver, CO, and the surrounding areas for more than 20 years. Our NATE-certified technicians are highly trained and have the knowledge and skills to keep your home’s heating and cooling systems functioning optimally throughout the year.

If you need to replace your old furnace or AC or are considering upgrading to a more energy-efficient model, we carry a range of units from major brands like Lennox and Mitsubishi. Our team also repairs and services most makes, models, and types of HVAC equipment including central AC, furnaces, ductless mini-splits, heat pumps, and more. We also specialize in indoor air quality solutions like air purifiers and filtration systems, and we have a team of professional plumbers who work on drain cleaning, water heaters, sewer repairs, replacements, and other plumbing projects. To learn more about reducing your cooling costs or get answers to questions about our other services, give the team at Summit Heating & A/C a call today.

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