Stop right there. Something isn't right. You say that the house was at 68 degrees, the furnace finally went on, and in just 25 minutes, the house is at 82F? The temperature increased 14F in just 25 minutes? I assume you have sense enough to know if that 82F reading is wrong and it's actually more like 70F. So, if what you say is true, your furnace would have to be sized to heat a whole apartment building.