Hi. Im burning a hearthstone mansfield for the second season now. I cant seem to get the pipe temp on the single wall pipe above the stove over 350 unless the door is open. I have about 3' of steel pipe, 90 into a masonary chimney about 30' high. The chimney sweep told me its good to get the temp up above 500deg twice a day to burn off. I am burning last years split oak right now. Any one else have this problem?