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Repiping Cast Iron Radiators

are using all the old radiators chances are that the design water temp (hottest water needed for coldest design temp)will exceed the 150 -160 degree high recommended temp for pex.

I would not take the chance with pex since it could fail when you need it most (at design temp) Your radiators were sized with a certain temp in mind and I am sure this temp exceeds pex piping high temp limit.

Unless you live in the southern climes I would say NO !

Rich K.

Make Peace our Passion while supporting our Troops!


  • Mike J
    Mike J Member Posts: 2
    Repiping for old Cast Iron Radiators

    I am having a 60 year old Delco Oil fired boiler replaced with a Crown Bimini 150 gas condensing boiler. The house is 83 years old. The current system is hot water closed loop, 1 1/4" iron pipe at the circulator, which expands to 3" and than back down to 1 1/4" as it travels down the line on both supply and return. I have a coal chute and assume that the larger pipe was due to the original boiler being a gravity feed. All radaitor feeds are 3/4"

    I am not adding any radiation. I want to raise the trunk lines up about a foot to the joists to create headroom in my basement. I want to cut and unthread sections of the 3/4" radiator feeds and replace them with shorter sections of 3/4" PEX with brass threaded couplings. Is this a viable option?
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