Pellet stove question or fireplace damper issue ?

[thinkxingu]

Not having a plate to seal off the chimney where the damper was is not uncommon--there are many different beliefs about this regarding lost heat vs. creosote build-up from a cold pipe causing condensation (non double-wall pipe).

If the chimney cap was sealed correctly, and the pipe is secured to your stove well, and you're getting a draft it's because you have negative pressure.

I'd probably call the installer to give him/her a chance to fix it before doing anything else--might be something simple they can remedy.