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Radiator Relocation-Hydronic

I have a new home with radiant heat. It looks like the system was converted from gravity to a circulation pump and a new boiler about 15 years ago. I want to relocate one of the radiators in the living room to the other side.

My question is, can route new plumbing for a relocated radiator make a small hop UP of a few inches where it ties into the existing line? Most of the existing plumbing is old iron pipe. However it is copper around the boiler and to a couple new radiators.


  • Any time that a pipe travels up and then down, the high part tends to collect and trap air. This isn't much of a problem in modern systems that can be "force purged" with the water literally pushing air bubbles ahead of them, but gravity systems (converted are not) are impossible to "force purge".

    If you utterly must route the piping such that it makes an "air trap" I have two suggestions:

    1) Add a simple air bleeder (just like on a radiator) to the high point(s) of the piping.

    2) Install a full-port ball valve on BOTH the supply and return branches as close to the mains as possible. This allows you to force water through in two different directions--HIGHLY useful in such a system.

    Again, presuming this is a converted gravity system your new branch piping should be the same size as the existing and certainly NEVER more than one pipe size smaller. Why?

    Unless you have TRVs (thermostatic radiator valves), if you pipe significantly smaller, the head loss to that radiator with increase greatly compared to the rest of the system and flow will be reduced if not completely stopped.

    My best advice when modifying original gravity systems is to pipe in a "monkey see, monkey do" manner. Not only in pipe sizes, but ensuring that all "horizontal" supply lines pitch slightly upwards away from the boiler and all "horizontal" return lines pitch slightly downwards towards the boiler. Do this, and you're nearly assured perfect success. Fail and you can either be "chasing air" or find yourself with serious balance of flow problems.
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