Cool! You may find that problematic. The idea is to keep the room sealed off from the rest of the house when you’re in there smoking. One service vent in an attic room (no matter how well insulated) with no return vent re-conditioning the air, removing latent heat and humidity may get a bit uncomfortable in the summer for example. If you open the door and the return starts sucking and blowing cigar smell through the house, momma may take issue.
I found out the hard way when I renovated mine, and ended up with a ductless mini split that did the job and was so efficient, that I noticed zero difference in my electric bill.
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