Mixing 1/2 PEX and 3/4 PEX in a single zone

dgkula

Question for the pros please: I have a single zone in my basement which is plumbed off a manifold with 1/2 PEX to 15' of fin tube (based on 3/4 copper pipe). I want to add a second radiator to this zone to heat a soon to be finished area of the basement. A plumber has proposed adding 8' fin tube and running 3/4 PEX, splicing that into the return from the 1/2 PEX, creating a single loop consisting of source >1/2 PEX > 3/4 fin tube > 1/2 PEX > 3/4 PEX > 3/4 fin tube > 3/4 PEX > return. Is this going to be OK? Naively I would think that single diameter for the whole run would minimize changes in pressure throughout the zone for a constant flow rate but I don't know if it matters. Of course an option is to have him re-plumb the original 1/2 for 3/4 PEX so that all diameters are the same but I have read that PEX expands as it heats ...

Thanks!
David

Jamie Hall

It's fine. Won't change the pressure much. The additional piping -- of any size -- and fin tube will increase the pressure drop around the loop, but not by much for that length.

Zman

Your 23' of baseboard will put out round 13,000 btu. You only need to move around 1.3 gpm. That should be easy with the piping you described.