Ultimately, none of it is a matter of what instructions say, or local code says, or what some inspector says...
It's a matter of what you are comfortable going to sleep with expecting to wake up, and in decent health, the next morning.
I say that from the vantage point of someone who, a long time ago, went to sleep with a situation that all of the above said was better than OK, and then woke up at 4 +/- AM to go to the bathroom and found I had a horrible headache and a house that was full of wood-smelling-fumes.
Wrong combination of appliance, slightly unusual weather patterns, and assumed norms of all of the "experts" who'd installed and inspected things.
I am, I think, P M F F- pretty miraculously ... something ... fortunate. If I had not needed to take a Wh** at 4 AM (and then, upon noticing the headache and smell, threw open the windows, damped the fire, and put some box fans in the windows in February) I am not sure that I or anyone else in the house would have awakened OK
Code, instructions, whatever?
Make sure you have uttermost confidence that you and the people who you care about will wake up the next day no worse.
such experiences helped reinforce my already-existing notion that a scrupulous self-DIY-er may often do a better and safer job than someone who is supposedly credentialed and who proceeds on the basis of "we always do it this way..."