outerface about 170F after 7-8 hours of running

[Dr.Pizza]

I think have some insolation problems with my oven. But can anyone tell me why the oven makes the perfect 90 second pizza and the floor recharge very fast from underground heat. Ok, outerface dome and under the heart is about 170F after 7-8 hours or more running with 850F. Temperature of 800-850 is reached in 60min-90min. But fully charged with heat to make good pizza needs 3hours of running. Otherwise the temp. of the cooking floor is falling dramatically with pizza in it. And i wondering why the heat is holding very good with low flame. I just adjust the fire shortly after 2 pizzas. So, why a lot of work and more insolation? Is it why i can safe 3 pieces of wood at the end of the day?? :_0
Or other reasons i dont know?