Builder installed a Hearth and Home Technologies heatalator EL36 into a new home and I want to install a wood burning insert. My understanding of what I have read, I will need a stainless steel 6 inch liner dropped down into the new 8 inch existing liner and a new cap. The fireplace has a slight offset, so liner needs to be flexible. I will probably opt for the Drolet model DB03125 insert that my local Lowes offers for the price. Question is, can this be installed into a prefab unit such as the model I have, and where is the best place to order everything to complete the liner install?