Question on flue size/draft issues with new woodstove install

Hello wood burners - have learned a lot from reading the posts on this site. First post for me - thanks in advance for your advice.
I am switching from a pellet stove to wood burning stove for next burn season (winter 2010/2011). Home is ~ 3000 sqft. Open concept 2000 sqft lower level and the rest of space upstairs (3 rooms). Large central chimney containing two flues - one for oil and one for fire place. Pellet stove is tapped into fireplace chimney flue on opposite side of fireplace. The tap occurs at the smoke shelf of the chimney, approximately 12-18" below the first tile. Fireplace flue is lined with 12" square tiles. My plan is to install a Hearthstone Mansfield woodstove, using the existing tap of the pellet stove. I have a few concern since the 12" flue tiles are larger than the 'guideline' of 3X the cross-section area of the 6" stove pipe. First - do you think I will have adequate draft? Again, I have about 20' of interior chimney, ~ 8' in the attic, and ~ 4' exiting the roof near the peak. So, I assumed that I would have good draft, even with large tiles, since the temperature difference between chimney air and outside air is likley quite high. Second - since the flue gases will cool within the larger flue space at a greater rate than within a 6 or 8" flue, should I expect high amounts of creosote near the top of the chimney? I am two years ahead on wood now, and will stay 2 years ahead, so I'll be burning very well seasoned wood. Lastly - is there a problem having a woodstove tapped into the chimney below the first tile? Thanks again for your help and have a very Merry Christmas!

Cheers

Thanks Daksy - I'm hoping to avoid the liner, as I would like to keep the fireplace viable. I know that it is a no-no to start a fire in the fireplace with the stove running, but I'd like the option to use the fireplace when the stove is down. Thanks again.

Just hoping some additional folks might weigh in with their thoughts......thanks!

Jim,

Thanks for your info - I'm assuming I may need to do the same, but will have to run a line through the ceiling and roof in order to keep fireplace alive - hoping to avoid, but perhaps I'll do as you did - give it a shot and then be prepared to run the liner if necessary. Thanks again! Cheers.

Thanks Todd and MrFixIt - I have been trying to convince myself that the large flue would be okay, but I think you are both correct. Stove is expensive and wood is a lot of work (though I like it!) - so why end up with a poor burn season after doing all of the initial work and expense. Sounds like a liner is the way to go. Thanks for your responses! Cheers.

Well - I guess I'm sold on the liner - checking prices now. Another quick question. Is there a specific liner system for a liner going straight up through a lower level ceiling, second floor ceiling, attic, and roof? I assume I'll be using stove pipe to the first ceiling, then the liner for the rest (boxed in on the second floor). I guess I'm wondering about heat issues with the pipe as it exits the first ceiling, etc. Are they insulated in such a way as to avoid possible combustion? Also, the above roof portion of the new metal chimney will be within ~ 1 foot of the existing masonry chimney. Do I need to extend this portion above the masonry chimney, or can it be level with the masonry chimney? Thanks! Cheers.

P.S. Only want the the fireplace for aesthetic reasons - it is in the livingroom and we love the fire at night (plus, it seems to make the wife a tad more frisky...... ;-) ). The heating aspect is obviously minor, although it does make the room cozy.