Fans Blowing in or Blowing Out? Settle the Debate, Montana

It's been a scorcher lately in Montana; we've had back-to-back days with highs in the upper 90s and even triple digits across a huge swath of Big Sky Country. Air conditioners have been running nearly nonstop for many of us.

In the Billings area, overnight temps haven't been dropping below 70 degrees until the wee hours of the morning, which means I usually leave the air on overnight. Yes, I'm dreading our power bill next month.

A few evenings have been cooling down before we turn off the lights for bed (usually after a thunderstorm rolls through), and when it does, I give our A/C unit a break and open the windows and turn on some fans.

Read More: Montana Wildfire Smoke Forecast

gray and black fan turned on in close up photography

Here's where the fan debate arises.

My spouse and I rarely disagree on much. But when it comes to which direction the box fan in our bedroom window should go, we do not see eye-to-eye. We have two windows in our room, and she believes that the fan in one of the windows should be blowing cooler air into the bedroom.

I argue that the fan should be blowing OUT one of the windows, causing cool air to be drawn through the room from the opposing window. I mansplain a bunch of mumbo jumbo about thermodynamics, airflow, and how it's scientifically easier to suck air out vs. blow air into a room.

The thermometer shows a very hot temperature.

What does science say?

Consumer Reports says you should direct your window fan to blow hot air out. Their HVAC expert noted,

You should place outward-facing fans on the warmer side of your home to blow the hot air out and inward-facing fans on the cooler side to draw cool air in.

woman in blue denim jeans lying on bed

But wait... there's more to the story.

Before I gloat, there's another important thing to consider. Experts at the Physics Stack Exchange forum chimed in on this debate and brought up a great point. While they agree that blowing hot air out cools the room temp better, a panelist wrote,

A human sitting in a chair in the room with the fan blowing in will feel cooler than with the fan blowing out due to the higher motion of the air in the room.

This is due to the way our bodies have a built-in evaporation system. When a fan is blowing air across our skin, it makes us feel cooler, even if it's not cooling the overall temperature in the room nearly as efficiently as a fan blowing hot air out the window.

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How about a compromise? I suppose we could set up a smaller fan on a nightstand to provide airflow to cool the skin, while using the "blow the hot air out" way to actually drop the room temp.

Stay cool out there. It'll be snowing before we know it.