When does smoke back up into the house?

I am wondering when does smoke back up into a house with a pellet stove? I am planning on going up 3-5 feet.

see the

Sticky: Tips on if Your pellet stove is burning lazy and or getting smoke in the house
at the top of the pellet room page
http://www.hearth.com/econtent/index.php/forums/viewthread/13419/

Normally... never.

If you loose power with a fire going you can get some smoke spillage, but with a good rise you will reduce it quite a bit.

Now if smoke rises, and I have a stove with a bottom discharge.............. how much does the venting after the stove help? :-/
Not really a trick question...........