Question: We now have a wood/coal burning stove. We recently bought a pellet stove from a friend. The pellet stove's exhaust pipe is much smaller than our existing stove pipe. We have triple walled pipe through the attic. How can we use the existing triple wall with the pellet stove? Thank you. Answer: Run the pellet vent pipe (either "L" vent pipe- or single wall stainless steel) up right thru the center of the triple wall. The triple wall is too big- and therefore too "cold" to vent the gases without a relining with smaller pipe.