Calculating GPM with BTU Loads for a Hydronic System

This is a video that explains the quick way to calculate US Gallons per Minute using the BTU load of a building. GPM is used for sizing pumps in a hydronic heating system.

[@jamalmarzouk8274]

Thank you , it is a great job

[@bpdp379]

How do I apply this in a zoned application where the zones are in a common area? I have a 2400sf shop where I did two zones in case I wall off the zones to have a separate warmer work area and a colder storage area. If the smaller zone is 25% of the area do I assume 25% of the flow?