I live in a forested countryside in the Northern Midwest. Leaving the windows open invites in bugs and other small critters. Even with screens on the windows, insects crawl through the cracks, and I’ve definitely had several field mice chew their way through screens. I also have rabbits and possums who tend to nest up against the foundation of my house, and if a lower window is left open for prolonged periods, I sometimes find babies nesting in the window frame.

If I open my windows, it’s for a limited time to get some fresh air moving through the house. I’ll turn on strategically placed fans in various rooms to encourage rapid airflow through the house so I can close the windows sooner.

I only open windows in the winter if I need to cool a room quickly. For instance, I’m renting my first floor to a friend and I live on the second floor. But I only have one HVAC unit and thermostat for the entire house. The first floor always stays a few degrees cooler than the second floor (heat rises), so I keep it a little extra hot upstairs to ensure I’m not freezing out my friend. But I’m always hot in general, so I’ll either have fans on me all winter, or I’ll occasionally shut myself in a bedroom and open the window for 15-20 minutes, just to lower my body temp a bit and help me tolerate the hot house.

There have been a few winter nights where my wife and I have left the bedroom window open to cool down our bedroom, while burying ourselves in thick blankets. We don’t sleep well if we’re sweaty and stuck to the bed. I usually get up a few hours later and close the window, so we don’t freeze overnight.