Wind chill does cool down warm or heated objects, just like our bodies.. but wind chill cannot cool anything below the real temperature..
So, if you have poor insulation, so your outside walls are warmer than ambient, and single pane windows, which are warmer than ambient, then wind chill will cool the building down faster than calm winds with the same ambient temperature.
So if you really want to come up with a mathmatical formula for life burning coal,, include the wind, figure out a coefficient for your windows, outside walls, infitraton rate, and insert them whereever in a formula..
Oh, don't forget internal orgainic heating.. that's the heat generated inside the house when you and the wife have a big fight, or the opposite, you are getting along and generate some extra body heat.
But the bottom line is: buy some estra coal, unless you think the Farmers Almanac is a scientific standard to go by..
And as mentioned above, just shovel it in as needed, and enjoy the heat..
By the way, did I mention that mathmatics gives me a major headache ??