Hey Guys! This is my first post so I apologize beforehand if there are any mistakes with my post :D But my question is... I have 2 water pipes that are connected to one pipe in the middle, but the distance from the 2 water pipes to the connection point are not necessarily the same. The distance from water pipe with 80 celsius hot water to connection point is 1 m, and the distance from the water pipe with 20 celsius cold water is 1,5 m(Like you can read I like to use SI-units). The water flows from to tanks placed above so the gravity force affect the water to flow through the pipes(A little sketch should be attached). I know the value of all most everything in this systems except the pressure, so feel free to ask. But How do I find the flow rate of the water from both the cold and warm water pipes when I want the output temperature to be 60 celsius? I found this calculator online: http://wea-inc.com/calc-frm.htm but I don't understand where this equation is from? I mean why do you need to use the specific water gravity? If there are anyone who can explain this equation or know how to solve this problem, I would be very grateful.