Question: Dear Folks Last year I bought a pellet stove from my brother in law When i got the unit it had type B dryer vent pipe and insulated pellet pipe combined. After checking prices i opted for single wall type B. I don't think the unit is working as efficiently as it was. What do you suggest? Answer: The pipe looks like class B, but it is actually Class "L", which has a stainless steel interior as opposed to aluminum. The class B is not up to par and is dangerous. This will make a difference in the safety, but not in the efficiency or operation. That may be due to another problem, most likely the need for cleaning the heat exchangers.