A: It's important to keep your brew jar as close to 74-76 degrees as possible, that is when the culture produces the most balanced ratio of yeast to bacteria. As you'll soon find, Kombucha brewing is all about finding balance.
It's fine if your brew drops as low as 68 degrees. However, if it goes below 68 degrees for an extended period of time it can be more prone to develop mold, as the bacteria and yeasts will start to go to sleep. The colder it is, the longer it will take to brew. And vice versa, the warmer it is, the faster it brews.
If your home is very warm in the summer time, its important to keep your brew jars somewhere cooler they won't get too warm. It's best to not let your brewing jars stay above 84 degrees for too long or your yeasts will begin to overpopulate and throw your brew out of whack.
Be sure to keep any heating methods like a heating pad in check. If leaving your heating element on all the time is keeping the temperature too warm, simply turn it on a for a few hours a day and wrap a towel around it to insulate.