Strongly suggest that you make sure that the exterior combustion air supply duct is attached. Do NOT get a unit without that feature!!!!!
Otherwise, such stoves can cause the type of back-drafting that I am taking about above with SERIOUS health consequences!!!
Beware!!! NONE of the fireplace installer I talked to seemed to understand this back-drafting issue. Find one who DOES and can do your job right.
I have a pellet stove insert myself. It was done without the special ventilation. I will have to fix mine before it gets too cold, or use other heat sources.
BTW, why an insert??? There are cheaper, cleaner, safer ways to heat.