Use Your Whole House Fan to Keep Cool all Night

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I’m a big “fan” of airflow. After moving into my current home, in the space of a few months, I had central air conditioning installed along with a ceiling fan in every room. In addition, I installed my favorite cooling devices, two whole-house fans.

And, yes, I run them all night

During the day, your house heats up, and you use your air conditioner as usual. But starting in the evening, if you live in a desert or semi-desert climate, the outside air quickly cools down. However, the house itself will hold the daytime heat for many hours.

You open your windows, but airflow is minimal, even with all your ceiling fans.

A whole-house fan is a different story. These fans are installed in your attic and are designed to pull air from an open window, through the attic and out. As a result, cool air is pulled in, and the leftover hot air from the daytime is pulled out.

With a whole house fan cool night-time air is pulled in, while stale warm indoor air is pushed out.

Your room will equilibrate with the outside air temperature.

Older whole house fans were famously noisy, but the newer versions are very quiet, no noisier than a regular fan.

The ones that I had installed were recommended to cover around 800 square feet or the size of one room. As my home is 1300 ft-sq I installed two.

The intention is to install one per bedroom with the intake in the ceiling on the opposite side of the room from the window, usually near the door.

Intake for one of my whole house fans

If you keep your bedroom door closed, and your bedroom window open, one fan will operate within the space to cool that room exclusively.

I run both my fans, leave my door open, and open two windows, my bedroom window and my kitchen window. This way air will circulate throughout my house “pre-cooling” it for the next day’s heat.

If you slept in a ground-floor bedroom you could still benefit if your window and door were both open and an upstairs room—such as a study—had a fan intake and an open door.

Needless to say, these fans are far more energy-efficient than your air conditioner. In the years since mine was installed, they’ve further improved the technology for even greater energy savings.

Using your whole house fan with voice control

I had mine installed over a decade ago before home automation. They were installed with a control panel that sits in my hallway right next to my thermostat. Originally, they were controlled by a standard spring-loaded timer knob. I would set the timer for several hours and go to bed.

This knob started to wear out, so I replaced it with a smart switch. This smart switch can be controlled by an Ap on my phone and includes a timer feature.

Switches to the right individually turn on and off my two whole house fans. Those are kept on at all times. The switch at right is a smart switch that can be controlled by the switch itself, a phone App, or via voice control.

Like all of you, I sleep with my phone (or rather my iPad).

However, I don’t bother turning on my phone to control the fans. I simply yell at Alexa to either turn on or turn off “the fan.”

When you are tucked away in bed, the last thing you want to do is get up, walk down the hall, and flip a switch. Reaching for your phone is much easier. But the ideal situation is to not even open your eyes.

In addition to having an App, this smart switch also supports integration with Amazon’s voice-controlled Alexa. Depending on your preference, it also supports other voice-controlled devices, such as Google Assistant and Microsoft Cortana.

Sometimes I wake up hot, having forgotten to turn the fan on. Alternatively, I sometimes wake up cold as the fan did its job a little too well. Either way, I can fix the situation without moving.

Eliminate bad indoor air

As I live in the temperate climate of Southern California, unless temperatures are extreme, I always have my windows cracked open. Smelly indoor air from either myself or my furry friends is quickly eliminated.

Not everyone can enjoy this luxury, so it’s important to take advantage of temperate nights to clear out the stuffy air in your home.

I addition to obvious smells, indoor air may pose health risks. According to the American Lung Association, indoor air pollutants may come from building materials, such as VOCs (volatile organic compounds) and carpet; allergens such as mold, dust mites (and pet dander); and cleaning supplies and other household chemicals.

Eliminate bad cooking outcomes

I don’t cook often. But there was that time that the lasagna overflowed and made a mess of my oven. I decided to use the “self-cleaning” feature on the oven. The oven bakes itself at a really high temperature in order to “burn off” stuck-on food gunk.

Big mistake. My home filled with smoke from the burning food gunk.

Yes, I have the required exhaust fan above my oven, but it was not up to this task.

Fortunately, the whole house fans were able to quickly clear out the smoke and I didn’t need to evacuate my lasagna-eating guests. (But more wine was poured.)

Run whole house fans during the day?

Most of the time there will be no reason to run them during the day. However, if you don’t have AC and your indoor temperature is equal to, or warmer than the outdoor air, then run them.

Close the flue?

If you have fireplaces where you burn wood, then don’t forget to close the flue or else soot and dust will be pulled into the house.

I’ve never bothered to close my flue and I’ve never had a problem. However, my fireplace is gas which produces little soot.

Bad outside air?

The one downside is that you are stuck with the quality of the air outside. If your neighbors have been enjoying their outdoor wood-burning fireplace, you may need to temporarily lay off the use of your fan.

If you are prone to outdoor allergies you may also have to limit its use. Pollen levels vary during the time of day, but can still be elevated at night.

Keep in mind that many allergy sufferers are worse at night. One issue is exposure to bedroom allergens: your pets plus the dust mites in your mattress and bedding. Another issue is that you are lying down and your nasal passages can’t drain as easily. Propping your head up with extra pillows may help.

Tip: add a mattress cover that protects against dust mites

As always, seek out the advice of your allergist if your sleep is impacted.

Not to be confused with attic fans

Another cooling device is to install a fan in the attic. These are designed to switch on automatically when your attic reaches a certain temperature. They are intended to simply clear hot air out of your attic, which should help your house cool down at night.

Unlike whole house fans, there is no intake from the house itself. Air from the living areas remains unchanged.

Photo by Al Soot on Unsplash

QuietCool® fans

Several manufacturers produce whole house fans, but the most well-known and popular brand is QuietCool ®. (I’m not affiliated, just a big “fan”.)

At present they offer four types of whole house fans with warranties ranging from ten to fifteen years. I have the older “classic” series which is working great after a dozen years plus. The newer fans are more energy efficient and have longer warranties.

All four models come in multiple sizes with different airflows.

To determine the proper configuration of fans, it is recommended that you have 2-3 CFM (cubic feet per minute) of airflow per square foot of home space. My 1300 square foot home should have 2600 – 3900 CFM of coverage.

The smallest “classic” is rated 1,472 CFM. As I have two of them, I have the recommended coverage of 2944 CFM.

As my ceilings are a standard 8 feet tall, my home volume is around 10,400 cubic feet. Therefore, mathematically my indoor air is being replaced every 3.5 minutes, consistent with their recommendations (10,400 CF / 2944 CFM).

The largest fans they offer have a CFM of over 7000.

Depending on the size and configuration of your home, you can have a “zoned” plan, like I have, with a small fan in each bedroom.

Alternatively, you can place one or two larger fans in a central location, such as a hallway or stairwell, and cover the entire home.

If your home is large it may be best to take a hybrid approach with small fans in the bedrooms and a large fan placed centrally to cool the shared living areas.

The only caveat is that you have attic space large enough to contain the fans plus additional space for airflow. The larger fans will need more space.

If you have a mid-century modern flat roof you may be out of luck.

Regardless of which brand you choose, you may be able to mix and match different CFM sizes to meet your cooling needs.

Want to learn more about the products mentioned?

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Liz Baker, PhD

Side sleeper, cat mom. And after many decades of nightly testing, an authority on sleeping in comfort. However, I'm still in search of the good night’s sleep I used to have.

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