I am in the Lehigh Valley and I am heating a 35 year old house so the insulation and windows are not that good. It does seem like you are burning a lot more coal than you should for what you are heating. I normally run my stove at about 2.5 to 3 on a scale of 1 to 5 or about 50% of its capacity by the amount of burning coal. During the coldest and windiest nights I did turn it up to 4.5 but I have not yet run it at 5.
I work in Bethlehem live in the poconos so there is about a 10 degree temperature differance on average.
My house is actually older that yours built in the '50's
If I run my stove at it's highest level the ash pan would over flow over night.