Hi, I am new here, I just bought a vermont castings intrepid stove non-catalist. Its being installed in the middle of the house and venting straight throught the roof. I have been told I need triple wall pipe through the attic and outside, I have found some web sites taliking about triple wall being replaced with double wall. What do I need? Also how tall should the flu be to vent properly. Thanks for any help on this, John