what is the effect of mixing 1" pipe, 3/4" pipe and 1/2" pipe

JR3_Home_Performance

How about now?

LRCCBJ

https://forum.heatinghelp.com/discussion/196956/what-is-the-effect-of-mixing-1-pipe-3-4-pipe-and-1-2-pipe

I fail to understand why you would ever spend the money to do this conversion. You already have 1" pipe on the main loop which is more than sufficient for the heating load for the building. I suspect your issue is the fact that various rooms are unbalanced…………some considerably warmer than others. On a monoflo system, this is very easily managed by installing some globe valves on the supplies that overheat the specific rooms. You experiment and close the globe valve slowly until the flow rate is decreased to the point where the radiator puts out a reduced BTU level. This takes effort as the response to the valve closure is non-linear. The first 50% of the closure might get you NOTHING. This is far less costly and time consuming as changing to a series loop which is fraught with risk if you screw up on the pipe size. To be completely safe with a series loop, you have to run 1". Who really wants to do that?

And, what happens if you are unbalanced once you install the series loop? Your options for control of individual rooms are NON-EXISTENT at that point!!

On one building I have a monoflow with 3/4" on the main loop. Now, there is a serious problem with 8 monoflo tees in the loop. I have a giant Taco 0011 on that loop and it still returns 30F DT at the boiler!! I wish I had your 1". I'd keep it forever and manage the balancing with globe valves, if needed.