Trick my Dad shared with me was to open the doors under your sinks in the kitchen and bathrooms. In particular where they are against an outside wall. Gets a few extra º to the pipes.
As far as windchills go, the National Weather Service changed how they calculated Windchill a few years ago.
»www.crh.noaa.gov/ddc/?n=windchil ··· hill#Old
»www.nws.noaa.gov/om/windchill/im ··· pare.pdf
With the old chart, -25ºF and 25MPH wind speed produced a -81ºF windchill.
So, jrs8084 was within the ballpark for Northern IL from a good cold snap with the right conditions.
I like the watts sq/m that Juggernaut quotes. I assume that is normal in "hydro" country?