If they're all at the same height, using a pump or 2, then literally it depends on how tall you are, and how tall the tallest kettle is. You'll want to be able to see and work easily into your mash tun and kettle while standing on the ground without a step stool. My stand is a gravity system, and the kettle is on the burner that sits on the ground. I started there. There are no set rules.