Temperatures Friday afternoon should reach the mid-40s but there’s likely a big change next week
https://www.nbcchicago.com/weather/stories/chicago-weather-281898901.html…
Every year the temperature drop quickly and because most of us have not been using our furnaces during the warm months, they often need maintenance to perform at their peak.
Having your furnace inspected and serviced every year is recommended by the manufacturers in order to get the full benefits from your warranty.