This Quick Trick Cools My Bedroom Without Blasting the AC

My home office, originally a master bedroom, is the worst room in my apartment cooling in summer. It feels like the roof does nothing to keep the heat out during heat waves.

It gets worse. The room is too big for a single central air vent to cool sufficiently. Next to my desk, there is always a fan running. (Needless to say, 85 degrees Fahrenheit is not ideal for working.)

Lately, I’ve been wearing a hoodie to keep warm after ventilating all night with the windows open in cool weather. It was fun. If I had kept the windows closed, my thermostat and air conditioner would have tried to achieve the same temperatures with the two box fans.

The bright future of renewable energy sources may lower energy prices in the future, but for now, ordinary Americans are feeling the pain as inflation drives up debt.

Reddit is full of threads from cost-conscious consumers trying to find ways to save energy — and reducing AC usage goes a long way.

Let’s explore how reverse ventilation works and some ways you can use it to reduce your cooling bill.

Cross ventilation can cool your home and save energy

Cross ventilation works because the air creates a pressure difference outside your home. The high side of your home experiences high pressure air flow, while the low air side creates a low pressure area. The pressure difference exists whether your windows are open or not, so you might as well close them.

By opening your windows, high-pressure air has a direct path to a low-pressure area — it’s easier to flow through the house than around it. It’s a great way to bypass your home’s insulation, which prevents heat energy from entering and leaving your home. If your home is cool enough, closing the windows and curtains ensures that the indoor air will warm up a bit.

If you want to use natural air for cooling, the outside air should be colder than the indoor air.

For example, I close my windows and turn on my AC after the outside temperature reaches 75ºF. Usually this is where my thermostat kicks in — about 72ºF in my basement. I keep the windows closed during hot weather — unless the night temperature drops below 70ºF before I go to bed.

Cross ventilation and air conditioning can coexist

If you are using an air conditioner or heat pump, you will see more energy efficiency if all the windows are closed during operation. This is because open windows and doors create a large gap in the building envelope, separating indoor and outdoor air.

Limiting the amount of air the AC unit must place means it won’t work as hard as when indoor air is constantly exchanging with outdoor air. In mild climates, free cooling works well enough to offset the heat from the sun that plagues my home when the temperature rises.

You have to remember to close the windows every day, but the extra effort is usually worth it. Before I started using cross ventilation regularly as a remote worker, my AC was at least twice as efficient. I have seen huge savings over the past few years.

Effective natural ventilation depends on many factors

According to the Department of Energy’s Office of Energy Conservation, the best people for getting natural ventilation are coastal climates and droughts. At the beach, you can use the cool sea breeze to help make your home more comfortable.

These regions are the most likely to experience the greatest drop in temperature at night, but you can also use ventilation in other areas. It probably won’t be as effective, especially if your local climate is humid, but it’s still a good option for fresh air.

However, the effectiveness of cross ventilation as a cooling method decreases as the outside temperature increases. Keeping windows open all day may end up allowing hot air to enter your home and stress your AC.

Similarly, poor air quality days are not good for open windows, so it’s worth setting an alert if you live in an area prone to air pollution.

It is not always easy to create a breeze. Static ventilation works best when the air blows directly through the window and through the house in a straight line.

Opening windows won’t cut it in a home where air currents have to navigate complex hallways and rooms to find a way out. All obstructions cause turbulence, so cold air can trap a lot of heat as it tries to flow into nearby living space.

For example, the best ventilation windows in my home are upstairs, which is more difficult to cool than a stable basement. This often means a temperature difference of at least 10 degrees in the summer — a comfortable 72 degrees at the bottom and a scorching 85 degrees at the top.

Unfortunately, the airflow needs to go around several walls to connect them. Without my window fans, there is a commotion in the hallway instead of a nice breeze passing through my office.

Create your own air with a window blower

Using window furniture to create cross ventilation is straightforward. The easiest way is exhaust ventilation, which uses a single fan that pushes the air out on the other side of the house from where you want the air to come in. This creates a negative pressure environment that draws air into your home and out through the fan. .

This method works, but it may not move quickly in strong winds, especially in large houses. Low air movement also means that potential cooling effects can dissipate into turbulence before reaching the exhaust fan.

We can usually overcome this by adding a second fan, which blows inside the other window in a process called balanced ventilation. A fan blowing air creates a high-pressure area that flows smoothly into an existing low-pressure area.

Although I use Lasko box fans from Walmart, you can also buy purpose-built window fans, like this model from Bionairewith reversible air flow, thermostats and retractable screens to close the windows.

Using smart home tech to control window fans

Let’s explore the basics of setting up my window fans:

• Box fan 1 brings air through the bedroom window.
• Box fan 2 draws air into the hall and office before blowing it outside.
• Each fan connects to a smart plug for easy control. I group them using a virtual switch so they work in unison.
• A Sonoff temperature sensor in the room causes the fans to run as long as the temperature inside is warmer than outside. It also keeps the room from getting too cold.
• I use a temperature deadband and a time delay to prevent the fans from constantly throttling near target temperatures.
• A window sensor in the bedroom prevents accidental activation when the window is closed while triggering automatic switching when I open the window.

I don’t have a smart thermostat, but you can connect one to these circuits to turn off the AC while the ventilation process is running.

For this to work, you need a smart home hub that can use temperature as an automatic trigger. Your best bet is something like Home Assistant, SmartThings or Ezlo, but I couldn’t find this option in Alexa or Google Home with my current smart home devices. I don’t have access to Apple Home, so I can’t confirm how it uses temperature in smart home modes.

While window fans work well in my situation, you probably don’t need them if your home already handles hot air like a pro. However, you can use smart home sensors to let you know when it’s time to close the windows and curtains for the day.

Fresh air ventilators

Window fans are probably best for renters and people on a budget, but you can also give your home a fresh air boost for your HVAC system. As long as you have a compatible system, Ecobee smart thermostats support cross ventilation with their free cooling feature. You can find similar performance in whole-house ventilation products like AprilAire.

I have no experience with whole house ventilation systems, so I recommend contacting a local HVAC installer if you want to add one to your home.

Frequently Asked Questions About Cross Ventilation