Not all set ups are equal- that's obvious. I do generally use 7.5 tons of rice coal a year with a KA-6. Wish it was less but house fairly big. Used almost 2 ton one summer running the coal for hot water. Last summer used the oil boiler from 6/15 to 10/5/12 and used about 1/4 of 275 gallon oil tank- say 70 gal of fuel oil. Roughly same money for oil fed side arm for the summer as ton of coal in my area. But the summer before coal for hot water was 2 tons.
My coal boiler is 4 feet from the oil boiler. I bought 7.5 tons and started upt 10/5/12. 1.5- 2 tons left right now. Again- lot of house with suppossedly good windows and R-21 walls and R-50 attic. But, Damn is it windy where I live! My wife keeps things at 72 degrees also. I tell to turn down the heat to save coal and her response is..... but I though coal was cheap.