Pipe sweating - Metal VS Plastic

I've seen how badly steel and copper pipes sweat in hot and humid weather, but I have not seem enough PEX to know how badly it sweats. Does anyone know if PEX or CPVC (and other plastics) will sweat as much? I'm guessing that it will sweat, but how much in comparison to metal pipe?
I'm asking this because I want to install some pipe inside my living space, because they are regularly freezing in the crawl space, and running heat tapes is costly on the electric bill, not to mention a pain in the ass to check in cold weather.
I'm considering using PEX or CPVC for this job. Most of these pipes will be going thru an interior wall, but a few feet will be exposed (and covered with some sort of wooden trim). But I dont want water dripping indoors that will cause damage.
Yes, I will cover the pipes with foam insulation, which I know helps a lot with sweating, but is not 100% preventive.
Thanks!
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snipped-for-privacy@spamblocked.com wrote:

I don't know where you are but my cabin has crawl space which is very well insulated. I have one hot air vent from my NG furnace located there installed. For more than 10 years, no problem. Plumbing is all exposed PEX down there. In winter it gets down to even -30F often here.
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I would think there would be no difference since the sweating - condensation - is caused by warmer and, consequently, "wetter" air encountering a cooler surface. A water pipe, regardless of the material, is going to be at whatever temperature the water in it is.
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On Sunday, January 11, 2015 at 6:30:59 AM UTC-5, dadiOH wrote:

I don't think that's true. The temp of the surface depends on how well the pipe material transfers heat. Copper is a great conductor of heat. Plastic isn't. If you look at a temp cross section of the pipe material, there is going to be a steeper gradient with the plastic pipe than the metal.
I can't say I've compared them side by side, but I can recall lots of metal pipes sweating, toilet tanks, faucets. But I don't recall seeing a plastic pipe sweat. I would agree that it's still possible, probably does occur under the right conditions, ie cold enough water, humid enough air, but I bet it's a lot less than with metal.
As to the problem, I sure wouldn't rely on cpvc not busting when it freezes. Pex would be better. Maybe I'm missing something, but it sounds like only a short run is really exposed to cold, so I don't see why it would be costing much to heat. It can also be on a thermostat, so it doesn't heat 24/7. And they have variable type tape too, where the resistance increases as it heats up, thereby regulating the temp/power.
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On 1/11/2015 10:30 AM, trader_4 wrote:

I've seen it, but it is an a humid environment and the flow through the pipe is well water at a constant 3 gpm. Never saw it in a residential application.
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On 1/11/2015 6:30 AM, dadiOH wrote:

I'd guess metal to sweat more. With plastic, the heat of vaporization (vapor condensing to liquid) will warm the pipe, and the plastic won't conduct more cold (absence of heat) to the surface of the pipe.
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On 1/10/2015 8:21 PM, snipped-for-privacy@spamblocked.com wrote:

the outside, but doesn't drip. The insulation should do. Liz
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Pour a cold drink into a plastic, metal, and glass cup. The metal and glass cups will sweat quickly because they conduct heat well. The plastic cup will take longer but will eventually sweat too.
I have exposed PVC pipes in my pumphouse and they do sweat in the summer time when cold water is flowing through them.
Cold pipe and hot humid air will sweat regardless of the pipe you use.

If possible, route the pipe so it is above the insulation on the warm side (from heating the house). Even if you have to build a soffit of some sort to lower the insulation below the pipes and keep them in the heated space of the house.
If the pipes must remain exposed, I would cover the pipes with foam insulation, making sure to seal up all joints. Then I would wrap that with fiberglass insulation, and finally a layer of plastic tape or other vapor barrier.
Anthony Watson www.mountainsoftware.com www.watsondiy.com
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