Hello..newbie here with 1st post. We recently purchased a new regency wood insert to replace a very well-used wood burning stove (came with the house when we bought it). The existing liner is an insulated rigid steel liner. Because it connected to a freestanding wood stove the liner has a tee and is about 3 feet too short to attach to the top of the new insert when placed inside the firebox. We were able to remove the tee and would like some advice on whether we can now connect an extender from the top of the insert to the to the existing liner. The store clerk thought we could, but we'd like to just double check. If we can, what are some recommended options? Do we need a rigid-to-rigid connection or can we use about 3 feet of flexible liner? Thanks!