How much R rating do you think I would need between this insert and combustibles. I would like recommendations on what r rating do I need on the top sides and bottom to lower clearances to combustibles to about 6". This fireplace is not designed for an insert. I bought a Drolet 1800i wood burning insert to replace my gas fireplace. I also bought 15' of duravent stainless 3 wall stove pipe to place in the false chimney. Some info you might need. The house is 2100 sq feet ranch style house, one level no basement. The fireplace is not centralized; it is located in the living room which is at the far end of the house. The house was bought in July and want to replace the gas fireplace with the drolet insert. The is not a modular home and is not a prefab house and it was built in 2005. I have more than enough room for this insert in the false fireplace. What I mean by false fireplace is that it looks like a fireplace all the way up through the vaulted ceilings and on top of the roof. It is studded and insulated like a normal house wall would be. I planning on lining the the false chimney with durarock just to be safe even though clearance to combustibles to the chimney pipe should not be a problem. The insert manual states distance to combustible for the sides is 12" and for the top is 20" but does not stated clearances for the bottom of the stove. What would your recommendation for safe r values for top bottom and sides of this stove? What materials would you recommend using to achieve this r value?