Am I blowing heat out the flue

I have acquired a house with a Heat n Glo propane zero clearance gas log fireplace. The flue is a six inch protrusion right out the back behind the house. The combustion air appears to come from the bottom front of the fireplace, inside the house.

Question: So how much of the forced air heat in the house is going through the fireplace and out that 6" flue? I have been busy sealing cracks, adding insulation, and getting insulated window treatments; I just now got to looking at the insert. I don't need the fireplace for heat, and with the open floorplan any "space heating" heats the entire house; any function the fireplace might have would be purely decorative. If I am losing any of my expensive propane heat out that thing it is a liablility. Any help would be appreciated.

If its vented horizontal its not a "gas log". Its a fireplace. Need a model number. Looks under the fireplace for a silver rating tag. Also considering its vented horizontal and it is a 6" flue you should have a direct vent model, which does NOT pull combustion air from inside the room. It pulls it from the outer pipe on the double wall direct vent pipe.

So for your question, the answer should be none of your heated house air is going out the flue when you run the fireplace.

You say "potatoe"... Yes, yes, gas log fireplace, that's what I asked about.

OK, combustion air from outside. That would explain the rather odd looking vent. And why it is so large. Great!

Thank you!