pex for BB hot water


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Old 06-08-07, 03:53 AM
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pex for BB hot water

What are the differences in pex and copper.What is OD and ID of 1/2 pex, 1/2 copper, 5/8pex , 3/4 pex,3/4 copper. Can pex and copper of same size be used interchangeable in say the same zone.What are some decent names in pex tubeing for use in BB hot water.
 
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Old 06-08-07, 04:18 PM
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PEX/Copper

Copper pipe is measured inside. Copper tubing is measured outside. For example: 1/2" pipe is 5/8" OD & 3/4" pipe is 7/8" OD.

Not sure about PEX. If you do decide to use PEX, make sure to use one which is non oxygen permiable. These usually have aluminum either inside or between the layers of PEX.
 
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Old 06-08-07, 06:42 PM
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PEX is pretty close in dimensions, but expands 10x as much and needs more support. PEX-Al-PEX has expansion rates similar to copper...
 
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Old 06-08-07, 08:17 PM
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I used PEX in my install here for baseboard heat. I used Wirsbo hePEX 3/4" and in this case the outside diameter is close to 3/4" and the inside diameter is just over 5/8". The fittings I used were part of the Wirsbo ProPex system, so the PEX is actually stretched over the fitting so you don't lose any diameter. If you go with a compression ring type system, you lose a little more diameter because the fitting is smaller than the pipe itself. I don't have any here so I dont know what the exact measurement is, but I know it is slightly smaller.

In my install, I used a combination of 3/4" copper and 3/4" pex without much of a problem. The pex needs more room to expand than the copper, but isn't nearly as noisy when it expands. You just have to make sure you leave extra loops or leave the tubing a little long when you make a bend in order to account for the expansion. I believe the official numbers are something like 1" of expansion for every 100 feet per 10 degrees. I wouldn't recommend using the pex in any case where you need a return inside of the baseboard heater. Use copper for that or you might run into a case where the pex expands and knocks off the front cover of the heater.

In heating arrangements, you also have to use the O2 barrier stuff, which is different from the potable water type, and a little more expensive. This is to keep the oxygen from permeating the tubing and causing the iron in the boiler from oxidizing.

My reasons for using Pex were twofold. The first reason was because I was running the pex through the original air ducts that were embedded in the concrete slab in my living room, so I needed the flexibility. It also saved a lot of soldering together short pieces of pipe when I did my upstairs, because it's flexible enough to go through holes in joists without cutting into short pieces. The other reason was cost. Pex was about 1/2 the price of copper, even when I included the cost of fittings.
 
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Old 06-09-07, 05:05 AM
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A note on restrictive fittings. Although compression type fittings for PEX will typically have a very narrow passage, the hit on flow isn't as bad as it might seem. If for instance the passage is only " in diameter, it is not effectively making the entire branch the equiv. of ", it just means that for each fitting, the water has to accelerate to a much faster speed for the length of about an inch. It does reduce flow somewhat, just not as much as we sometimes think. The impact doesn't end up being so bad because it is for such a short length. I know I've had difficulties getting my thick skull to accept this.

Perhaps, if you need to flow a full 40,000 BTUs through a 3/4" branch and your GPMs are already near the minimum you might want to forgo compression fittings, but otherwise, they do offer a reliable PEX connection method for people that don't have expansion tools.

"This is to keep the oxygen from permeating the tubing and causing the iron in the boiler from oxidizing." Actually, the EVOH layer on PEX tubing is just a retardent -- it slows it down significantly - but doesn't stop it completely. PEX-Al-PEX has an advantage in this regard since oxygen can't permeate the Alu layer.
 
 

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