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When using a fart fan I often close the bathroom door to around a 10° angle. I have no real idea why except for this strange notion that limiting the fresh air intake might increase air pressure and somehow accelerate the stale air in the room up through the exhaust.

Which clears the smell quickest: fully open door, mostly closed door, somewhere in between?

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The way I see it, closing the door completely will force the outside (fresh) air to come from underneath the door (One might have experienced this if the fart fan is slightly low and we are in the path of the air flow). The flatulent air on account of being lighter rises and exits through the fan. By completely keeping the door open this entire process is slowed down. Which will work but will take longer. If the intention behind almost closing the door is of ensuring sufficient external pressure to force the stale air to exit as soon as possible then the best option is to shut the door completely in conjunction with the fan.

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  • $\begingroup$ I like your thoughts about upward airflow, but I don't feel like it gets at the spirit of the question. What size should the gap at the bottom be? $\endgroup$
    – Joel Mellon
    Aug 19, 2021 at 22:17
  • $\begingroup$ I did a couple of experiments with kitchen exhausts.. and I agree my previous answer raises more questions than it answers. However the key observations let me lay out. 1. The placement of the exhaust vent w.r.t the door. The reason could be that circulating air pockets form instead of the warm air venting out. 2. Coming to what you asked. The larger the gap (at the bottom or wherever) the slower the warm air exits (for a given fan capacity). Again these are my observations until I think of a more concrete answer. $\endgroup$
    – NormTrotsky
    Aug 21, 2021 at 4:24
  • $\begingroup$ That definitely answers more of the spirit of the question. I think I'm still looking for some sort of scientific explanation of how the airflow works with regard to air pressure vs velocity or whatever. Thanks for taking the time to reply. $\endgroup$
    – Joel Mellon
    Aug 21, 2021 at 17:53

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