Using PEX for radiator lines?

I am tempted to replace the old iron pipe that my house uses for the heating runs. From the furnace it is copper as you can see in the picture, and then goes into the older iron pipe.

The main reasons for wanting to replace it are that I want to add zoning. Also, the pipes hang down about 1.5' from the joists, which tends to catch my head when I'm not paying close enough attention. I also want to move the radiators around a bit, and copper/etc would be easier to work with.

Originally I was just going to use copper, but I started to wonder if PEX would work? Copper keeps going up in price. I also like the fact that PEX is solid and I won't have joints in the walls. Not a big concern since I'd pressure test it, but still. PEX is distributed by nature, so it seems like it would in therory work well for this.

I'm just starting to think about this project. It may be something I try and tackle this summer/fall as I currently have the living room gutted and have access to run the pipe in the walls.

Any thoughts?

What water temp and pressure does your system operate at? Pex has limitations in those areas. It works fine for in-floor radiant stuff because that is usually in the 110-140 range. Check the specs, most start to be derated at around 180-degrees F. Not sure of the pressure. Might work.

jadnashua said:

What water temp and pressure does your system operate at? Pex has limitations in those areas. It works fine for in-floor radiant stuff because that is usually in the 110-140 range. Check the specs, most start to be derated at around 180-degrees F. Not sure of the pressure. Might work.

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I'm pretty sure it is under 180* - if I remember it is around 160*. As far as pressure, there is a reducing valve on it now and it runs around 10-12 PSI.

I may find out this week, it is supposed to be a bit cooler here over the next week. The radiant flooring is what got me thinking about it originally.

If it's within, but close to the margin, you might want to consider not using it. Could a malfunction PRV or boiler exceed its limitations? Think of spewing boiling water all over your [insert prized possesion here] when it busts in [location of prized possesion]. I dunno, not to start a flame war here, but I never liked PEX anyways...

Jason

Do you guys have any suggestions for sizing the pex or copper lines?

The main line from the furnace is 1.5", which is reduced about 1' later to 1.25" (this is the part you can see in the picture). That goes into the 'T' which are then reduced to 1", and then into the large iron pipe. The branches from the iron pipe are 1" as well into the old cast iron radiators.

To me it seems inefficient because you have the large diameter iron pipe (it was already reduced from the source) that is just holding a larger supply of water. It has to heat this up.

I was thinking of running the 1.5" pipe, and then using T's to create the outlets for each zone (3 total). From each zone I would have a distribution pipe with T's for each radiator. (see pic) There are going to be 2-4 lines off of each distribution pipe.

What size do you guys think I should use? I have a feeling 1" would be overkill since the main distribution line is only 1.5". What about the rest, does that make sense?

It is not clear if your system is steam or hot water.

Your drawings show no return lines, suggesting that it may be steam with condensate returning via the same line. I don't think that PEX would work for that.

If you have hot water, then 3/4" copper is probably big enough for each of the three zones.

Bob NH said:

It is not clear if your system is steam or hot water.

Your drawings show no return lines, suggesting that it may be steam with condensate returning via the same line. I don't think that PEX would work for that.

If you have hot water, then 3/4" copper is probably big enough for each of the three zones.

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I figured the return lines were easier so I didn't include them. It is hot water though and runs around 160*F @ 25 PSI. So, it's within the specs for PEX.

I was thinking 3/4" as well. If copper weren't so expensive now, it'd be an easier decision. But I do like that PEX would be connection-less in the walls, and is freeze (burst) resistant.