Do You think it would be a common occurrence to have the windows open while the fireplace was lit?
It’s not a chimney, it’s a vent.
Look up the manufactures specs (located inside the fireplace unit) for the specific appliance for it’s listed and labeled install requirements.
Here is the standard guide for B-vent.
Probably only at my house, Jim. My wife feeds our wood burner like she is a stoker on the Titanic! I have to open the windows!
sadly I understand Sir…
Some ppl would. So if the window is open is it to close ?
Welcome to our forum, Scott!..Enjoy! 
Is that a B vent? Rules for B vents are very specific…A B vent has to be 8’ from a side wall…If it’s a direct vent then almost anything goes…(not really) but close…check this link for overview of B vent requirements Charleston Home Inspector Discusses Gas Vents | Blue Palmetto Home Inspection
Thank you it’s a direct vent fireplace so I guess anything goes
Scott, you were given an answer by Dominic… it is appliance dependent. The clearances will be stated in the installation manual for the fireplace.
I seen that and have read it thank you. It just crazy how close it can be to a window that opens.
I guess that would depend on how the wind was blowing…
Not the point. Think like a professional.
Gas Appliance Direct Vent Clearances
That is hilarious.
What do you think is ?
Well first , I did not comment on this article. So not sure what to say. Sorry? Hmm how can i get Hacked here ? interesting. And from what i can see of the picture the Termination of the chimney looks to be short of the 3 feet over the peak or highest part of the roof.