.The tech that installed my Harman p35i was really nice and im sure during the summer paying him cash on the side.He can do the oak that raps in the chimney.like in the owners manual.I just don't know if it's really worth it.I understand how the oak wrks. Has anybody with a insert here added a oak at a latter time and noticed a big result. My house was built in the 50s and I insulated it pretty well.thus far this stove has more than metting my heating goals and then sum. Just don't know if spending the extra $ is worth it. Kinda like if it's not broke don't fix ya know.i have seen most of the threads here on oaks and see a lot a different opinions.