Return water temperature.

cutter

Currently I have a thermometer on the main return line just above the pump. When my wood boiler system is up to temperature the return water runs 5 degrees colder that the water in the boiler. I do not have a clamp on thermometer to put on the individual zone return lines. My thought was to shoot the zone supply and the same zone return with a temperature gun. It takes awhile to get the copper tubing as hot as the water in it. So I would say it would take awhile to cool the copper pipe down if you closed down a balancing valve a little to get the water to flow a little slower through the zone.



Question is what should be the temperature difference be between the supply and the return line of a zone? How is the process done correctly?