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Thread: My plumber stubbed out to my cast iron radiators with pex, now what?

  1. #1
    DIY Junior Member dls's Avatar
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    Default My plumber stubbed out to my cast iron radiators with pex, now what?

    Two years ago my wife and I purchased an 1873 Mansard Colonial. Over the last 18 months we've done a great deal of work to it. As part of the rehab, my plumber ran new 1 inch Pex (Uponor) to the cast iron radiators. For reasons that remain unclear, he stubbed out one of the rooms in Pex rather than copper or cast iron. My question- would anyone like to weigh in on how to make the connection to the cast iron radiator look good? These are highly decorative radiators and the thought of having pex showing or a chrome sleeve adjoining brass makes my stomach turn. Any pics or advice would be greatly appreciated. Final note- the plumber is no longer on the project and I would like an idea of how it should be done before getting someone in here to finish the job.

    Many thanks!

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    In the Trades mtcummins's Avatar
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    I assume this is a hot water system, not steam?

    Even still, as much as I like pex, i wouldn't want to see pex used for a radiator system. You're flirting with its temperature limits. Its good for radiant floors (which usually are operating more in the 125 degree range), but I'd be wary of using it for radiators, which usually operate in the 160-180 degree range (180 is usually the max rating for the piping). I think Uponor might actually have a max 200 degree rating (if memory serves me right), which would ease the concern a bit.

    That's not to say that it can't be done, but you better be careful with your controls and run a conservative temperature, which might require higher pump speed to provide adequate heat.

    Is there no access to make a transition from the pex to a brass stubout? You might be best off making a hole in the ceiling below if necessary to make the change.

    I think the O.D. of 1" is 1 1/8". You could probably slide a 1 1/4" pipe over top of the exposed pex, make the pex connection, then slide the pipe back up and hold it in place with an escutcheon.

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    Moderator & Master Plumber hj's Avatar
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    Cast iron radiation SELDOM runs a 160-180 degrees. There would be a serious "scald/burn" issue if they did. However it has to be "oxygen barrier" PEX for a heating system , otherwise you are going to introduce a lot of future problems into the system. There is NO way to make the connection look good except to get rid of the PEX through the floor or put a cabinet over the radiator.
    Licensed residential and commercial plumber

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    In the Trades mtcummins's Avatar
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    It may be that some more modern systems (which usually aren't CI) have reduced that temp, but those are the standard numbers for hot water heat. Its how pretty much every hot water radiation system was sized historically, unless there was some reason to do otherwise. We know now that many of those systems will run better at a lower temperature, if properly sized to do so, but most of the older systems were sized for this Delta T at this level.

    The other thing that we see today, is that people have turned down the temperature on old systems b/c they were originally sized for no insulation, single pane windows, and if they were installed in the right era, to heat a BR with the window open all night (hysteria about air contamination). Now that all of those things have changed, the heat loss is different and the radiation is oversized, so we can turn the temp down and get comfortable heat.

    If 160 is a serious scald/burn issue, what about 215 degrees in steam?

    It just takes once, you learn not to touch that hot radiator. Its character building
    -mike-

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    Moderator & Master Plumber hj's Avatar
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    quote; what about 215 degrees in steam?

    Even worse and my brother had a big scar on his back his whole life from leaning against one. Baseboard heating runs a 180+ degrees but not hot water radiators. They have enough mass to compensate for the lower temperatures.
    Licensed residential and commercial plumber

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    In the Trades mtcummins's Avatar
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    The reason for CI not being run that high is b/c the heat loss has been reduced in the building. Then you get overheating, so you turn down the temp.

    The old school systems were almost always designed for that range. We don't run the old systems that high anymore b/c we no longer need to with them being oversized for our heat loss, but its certainly very normal for hot water heat to be run that high. Or at least it used to be.

    Today, more and more systems are designed to run more in the 140 range. As long as they're designed for this, its mostly for the better. My radiant floors run at about 130 most times, and about 140 if we have a really cold spell. Of course that leaves the wood/tile floors only about 80 degrees, so its a whole different animal.

    Steam radiators work great, and you learn quick not to touch them . I manage a bunch of property with steam systems. It hurts when you touch a fully hot radiator, but I wouldn't say they're a major burn issue... most of us have probably at some point in our lives lived in a building with steam heat, and we all survived. Not sure how your brother managed to get that bad of a burn from one... I get burned by them quite frequently, never anything that even blisters up, let alone scars. Seems to me that you'd have to stay leaning on it for a while to do that. Or the temp would have to be REALLY high, which would mean the boiler pressure was set WAY too high.
    -mike-

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    Retired Defense Industry Engineer jadnashua's Avatar
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    FWIW, both children and older people have thinner skin than a typical adult. As a result, they can be burned MUCH quicker, and one of the reasons the code mandates max temp in WH and implemented the anti-scald shower valves.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Moderator & Master Plumber hj's Avatar
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    quote; Seems to me that you'd have to stay leaning on it for a while

    I couldn't tell you because I was even younger than he was when it happened. But it was a "major" burn and a very large scar, almost like he had sat on the radiator.
    Licensed residential and commercial plumber

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    In the Trades mtcummins's Avatar
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    Quote Originally Posted by jadnashua View Post
    FWIW, both children and older people have thinner skin than a typical adult. As a result, they can be burned MUCH quicker, and one of the reasons the code mandates max temp in WH and implemented the anti-scald shower valves.
    This makes good sense, thanks Jim
    -mike-

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    DIY Junior Member jenylio's Avatar
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    A suitable heat resistant wet paint must be used to coat the Cast Iron Radiator . Do not accept a powder coated finish. Powder coating is without doubt an excellent durable and tough finish. However the process involves curing the radiator in an oven at temperatures of 200 degrees centigrade. This will damage the gaskets.

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