Okay I got yah. I'm actually only growing 3 plants in a cupboard. I'm just learning I do have a big fan on them so I will keep it that way. I have no windows open in the room ever as don't want bugs getting to it and door is Always kept closed to contain the smell me for I get in troubleA good ventilation fan is essential during all stages of a plants life. It evacuates hot, humid air from the garden and allows cool,dry air to enter. This makes it easy to keep temperature and humidity at proper level at all times. A garden without ventilation will become too hot and humid pretty fast which affects growth.
Plants also use up all available carbon dioxide in a room within hours so new co2 rich air must be introduced into the garden at a regular basis. Co2 is crucial for photosynthesis and overall health of plants. If you are only growing a few plants you may get away without a fan by opening a window or door nearby. Larger gardens should always have fans to ensure rapid growth and to avoid problems
Still learning at the moment and thanksYou need a good grow plan . Reacting to problems are a sure way to have constant problems. There are formulas for air movement in relation to space of grow. But you need to know how much heat, smell , and millions of other issues you can deal with or your playing roulette . Things get more complicated in flower and to harvest some that was worth the trouble you have to be on top of it.
Best of luck to you.