Converting Wood Burning fireplace to Pellet Stove.?

I have a smaller wood burning fireplace and would like to put a pellet stove in its place to heat the whole house and for how easy it is. I have a 6 or 7 inch stove pipe going into the wall that goes into a chimney which is outside. I was wondering if the stove pipe for the pellet stove will adapt with the original chimney for the house. Also is the stove pipe smaller then the one for the wood stove? Any suggestions or comments or any input on the subject would be greatly appriciated.