Exactly what you said... you can't get the humidity down unless you open the doors... or get some sort of dehumidifier... or set-up an exhaust fan to bring humid air out and dry air in... they have fans that have humidistats and thermostats to turn the fan on and off when it's needed. Proper humidity is very important for a number of factors. Too much humidity and you will possibly over feed your plants. Too little humidity and they can starve. The temperature is so important, too. Keep it dialed in to prevent mold and mildew. The plants are sitting in a pot of regularly damp soil = humidity source + the plants suck water up through the roots and stems and release about 90% of it into the air = so much humidity you need to get rid of it on a constant basis... especially in flowering stages. Good luck!😀