In my house - which I've owned for about 18 months now, there's a
fireplace with a natural gas burning log set... wifey and I were
looking at it last night, trying to figure out if it actually threw
any heat - or was it purely for the nice-fire-burning-atmosphere...
anyways, I turned the gas off months ago when we bombed the house for
bugs. And I couldn't get it lit and didn't want to spend all night on
it. That's not my question.

In the course of looking at the fireplace, I noticed that something
was placed in the damper to keep it from closing fully. But oddly
enough no cold air was blowing down the chimney...

The question - since the damper is open, I am now questioning whether
or not the log set is vented or vent free. Is there a way to tell?