Using PEX for radiator heating

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lxshteyn

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Hello. I'm an innocent victim of converting steam heating system to the hot water one. The plumber we are using recommends using PEX instead of copper. I read specs on PEX and it looks that they've been tested up to 200F. What is the common temperature people set on an boiler for heating cast iron radiators? Did anybody sucessfully completed similar project? Any feedback is really appreciated.
 

Jadnashua

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It's not uncommon to have a boiler reach 200-degrees (or more - remember it is under pressure like your car's radiator, so it can go above 212 without boiling when all is working properly). Most hot water boilers can't be set above 205 from what I've seen. Since you radiators were designed for steam, unless you run the boiler hot, they may not be able to give you as much heat as you want on a really cold day - depends on how it is sized. The pressure in this kind of system is low, typically in the 15-20 pounds range. Double-check the specs on the pex, and use one with an oxygen barrier if it works out. Are the radiators on a single pipe, or do they have a return line? You'll need a return line to run hot water. You might consider replacing the existing radiators with baseboard hot water units, then you could size them appropriately.

To do this right, you really need a heat load analysis, otherwise, you'll be shooting in the dark. Many older systems are really oversized. A boiler runs at its most efficient if it runs all of the time. I just had a new one put it, and it has an outdoor reset control that monitors exterior temp and adjusts the output of the boiler. It's only been in for a week or so, but it seems like it keeps the heat very even and when I look at it, the operating temp of the boiler is often in the 110-130-degree range unless it is reheating the water tank (where it goes to around 190).
 

lxshteyn

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Thank you Jim. I'm planning to replace old steam radiators with the new cast iron ones that go in the wall. I'm still confused about PEX vs. copper. If we put money aside for the moment then is copper a better choice?
 

Jadnashua

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Copper is a well-known commodity - it should last a very long time. PEX has been in use in Europe for longer than here,and so far, has had a good rep. Not everyone follows the "rules" when installing pex, and that can compromise things. If you don't with copper, it is easier to find and repair. Mice like to chew pex, I'm told. Pex is cheaper and easier to install, and should last a long time. The price of copper is still quite high, it may start to come down since they settled the strike at the biggest copper mine in the world, but it will probably take awhile.

You have more joints and difficulty installing copper, therefore, more chances of leaks. It's a tough decision, as either should work for a long time. Copper will radiate more heat on its way to your radiator, which may not be a bad thing. PEX probably won't make noises as it expands and contracts as can copper (if it isn't installed to allow for it). PEX is unlikely to split if it freezes, copper is.

Lots of things to consider.
 
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