This lets you easily check to see if it's hotter inside than it is outside and open windows/turn on fans if necessary.
If
Current temperature drops below
This Trigger monitors your local temperature and fires whenever the temperature drops below the value you provide.
Then
Send a notification from the IFTTT app
This action will send a notification to your devices from the IFTTT app.
Explore more great ways to automate Weather Underground and Notifications