I am installing a gas stove in my kitchen, [a Napoleon] and have boxed in the fire stop for the through wall install. I have a 9" by 10" boxed out opening, my pipe is 7 inch. Instructions say to install the metal wall flanges [inside and outside] after pipe is installed. So my question is can I put insulation around the pipe between the fire stop and pipe? It is the style that the center pipe is exhaust and outer pipe is cold air intake. Just seems to me I will be getting alot of cold transfer if I don't insulate. Thanks Dave