Any concerns with mixing PAP and Black Iron?

kyle_h

My fiancée and I are currently restoring a 1910 home in Pittsburgh, PA and after some floor plan changes are ready to hook up a couple radiators we had to relocate. The system is hot water heat with a circulator and a majority of old black iron pipes that are obviously way over kill. Each radiator is fed/returned individually off the main 3” supply and return pipes.

We would like to start transitioning to using Fostapex for the radiators that are currently not hooked up for a number or reasons, but want to make sure there would be no issues with have a system of mixed supply/return lines.

System goes Boiler -> 1-1/2” copper -> 3” iron mains -> 2” iron -> 3/4” or 1” iron -> TRVs

We would be using a hex bushing to connect the 1/2” Fostapex directly to the 3” iron supply and return mains and then a short 3/4” iron pipe off the TRVs with a male->press pex fitting to connect the Fostapex lines below the floor. The return side off the radiator would be similar; short iron pipe connected to male->pex fitting beneath the floor.

So with that said, is there any reason we should NOT run a mix of pex and iron piping? The system would stay this way until next summer when we could disconnect and replace additional lines. The big goal being to eventually remove all the iron piping and go to a manifold system.

hot_rod

In a closed loop hydronic system there should be no problem mixing metals and plastics, composites, etc.

Corrosion and electrolysis can become an issue with fresh water being added frequently, (leaks) or O2 ingress through non barrier tube for example.

You are on the right path to convert to a manifold home run system.

Hydronic conditioners could be addd for additional protection, I suspect with large diameter piping the system may hold a lot of water.