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Moving from series loop finned baseboard to parallel cast iron - how to pipe?
My 20 year old home has finned baseboard and I added an outdoor reset a few years ago. This helps keep the boiler temp down at somewhat warmer outdoor temps. Obviously, convection is pretty poor as the water temp gets lower so I have been moving toward replacing the finned with cast iron. The Runtal UF seems to have very good BTU/ft output and it looks like I can even go with slightly shorter emitters. But my loops are plumbed with 3/4" (M) and the Runtal units are 1/2" so a series loop (my first floor is 45,000 BTU) will not have adequate flow. It occurred to me that if I moved to a parallel loop I could leave the copper in place as a supply, and run orange pex alongside for the return as I replace each baseboard section. I would use 1" pex so the ID is fairly close to the 3/4" copper.
I should mention there are 6 zones all together and a few years ago I replaced the existing Taco 010 with a Taco Delta-T Variable (I think it's a (014). This helped even out the heating at 20* DT so I'm inclined to keep this in place if it seems rational to do so.
I learned alot from Dan's books (and this site) and my system is much improved as a result. But if there is a Mod/Con in my future, I think the additional mass of the cast iron will be a real advantage. I've never had a parallel configuration - only series loop. A few questions for you wizards:
Anything wrong with this approach in general?
Any negative effect of having different size parallel legs? - There will be 3ft and 8ft sections next to each other.
Will the flow balance out or will I have flow issues at the far end? Any reason to step pipe sizes up/down to compensate?
Do I need to use monoflow valves or something else like that where each section is dropped off the main lines?