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Retro and new fittings with PEX

stevef Member Posts: 2

I am furnishing a basement in a 1924 Chicago Bungalo. I am adding four baseboard units in a basement and refitting four existing radiators on a first floor. I want to refit the rads on the first floor to eliminate low-hanging pipes from the original gravity-fed hot water system. This is a DIY project, mainly due to budget restrictions.

The existing boiler is on its last legs and will need to be replaced.

I've been reading as much as I can on the internet about radiant heat specs and never realized how much went into designing a system. I've also looked for information describing installation of PEX but have found nothing. I've checked building codes and PEX is approved for hydronic heating systems. I have the following questions and would appreciate any guidance from the wall.

1. Can I use 1/2 inch O2 barrier PEX to service three large and one small radiators on the first floor?
2. Can I use 1/2 inch PEX two-pipe system for two of the large radiators, which are right next to each other?
3. Can I use the PEX to join two baseboard units in different rooms on opposite sides of the same wall using a two-pipe system?

Thanks in advance for any comments.

Steve F.


  • Zman
    Zman Member Posts: 7,441
    It is pretty unlikely that 1/2" pex is going to give you enough flow to distribute evenly through the existing gravity piping.
    If you post a drawing including pipe sizes and approximate distances of your existing setup and what you are proposing, you will get better advise here.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • stevef
    stevef Member Posts: 2
    Zman: Thanks for the reply and for the suggestion of adding drawings.

    The system doesn't rely on gravity any more. The current boiler has an electric pump.

    The back half of the house has had the old pipes replaced with 1" type M copper -- seems to work ok. That bit is on a two pipe system to feed three large and one small radiator. I thought a zoned system with a manifold going to each of the units would work for both first floor and basement units.

    The deep black lines represent placement of existing radiators (first floor) and future baseboard units (basement).

    I estimate the runs to basement baseboard heaters to be 45 feet for the four closest and 60 feet for the farthest.

    The runs for the radiators on the first floor 50-55 feet for the two big radiators, 35 feet for a small radiator, and 30 feet for the closest, large radiator. If I go directly from the boiler to the closest radiator, the run will be 15 feet.

    Thanks again for input.

    Steve F.imageimageimageimage