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Radiator re-pipe. Copper or Pex?
I live in a 90 year old house in the Philadelphia suburbs that has hot water heat and nice old radiators in every room. The house is about 1400 square feet and has 9 radiators of various sizes. The system was originally gravity fed so it has 3" black iron pipes suspended from the basement ceiling. Now I need to move all of the suspended radiator piping on the west half of the basement ceiling because I'm finishing the basement.
About 9 years ago the heating system was converted to gas (from oil) and changed from gravity fed to pumped. The boiler is a Weil Mclain CGa 5, 117,000 BTU unit. The installer ran 1-1/4" copper piping to and from the boiler to the original 3" black iron pipes.
I'm very much a do it yourself plumbing person. I've completely removed all of the original black iron water piping in the house and replaced it with copper. I've also done all of the plumbing (and electrical, structural, tile, finish, etc.) on 9 bathrooms and 3 kitchens over the years so I'm very comfortable sweating copper pipe. However, I have never worked with Pex.
I was discussing the need to remove and replace the black iron piping with a contractor friend and he suggested using Pex as far easier and less costly than copper pipe. A bit of digging here and on the web seems to confirm that it's doable, but my lack of experience with Pex concerns me.
I would start by demolishing the 3" black iron, leaving the smaller iron pipes (a mix of 3/4' and 1") that run directly to each radiator un-touched. Then I have a few options:
1) Cut the existing 1-1/4" copper, sweat new 1-1/4" copper to it, route the new 1-1/4" copper where needed to feed the radiators, and use fittings to reduce to 3/4" copper pipe running to and from each radiator. I'd use threaded brass fittings to join the new copper pipe to the existing iron radiator pipes.
2) Cut the existing copper, connect 1-1/4" oxygen barrier Pex, route the 1-1/4" Pex where needed and use fittings to reduce to 3/4" Pex running to and from each radiator.
3) Cut the existing copper, sweat manifolds to the supply and the return pipes, and run 3/4" oxygen barrier Pex from the manifolds to and from each radiator.
I'm comfortable with option 1 because I know I can do the job, but it appears to be the most work and the most $$$ by quite a bit. Option 2 appears OK, but option 3 seems a bit more elegant. With both 2 and 3 I'm concerned about using a product where I have no experience in a demanding application and pretty big consequences if it fails.
I'd looking for advice on the right way to proceed. Thanks!