I didn't want to bog down my post with too much information, but to clarify, I added a 40 Imp. gal Giant brand (made in Quebec) electric water heater in series to the 75 US gal Marathon water heater I spec'd for our house, completed last year. The 105 gal Marathon I initially calculated would be enough for us is not available in Canada. The 75 US gal Marathon is mostly adequate, but the Mrs. wanted a greater reserve capacity, so I am experimenting with this set up. We have 43F incoming water temps in winter. In a few years I want to finish the mechanical room, and then I will buy a second Marathon tank. We have very hard water, 36 (thirty six) grains, with a 70,000 grain softener. I want Marathon tanks due to their polybutylene/fibreglass construction, so no need for a rapidly consumed anode rod, nothing to rust. I know this steel tank won't last long with my heavily softened water, so I just bought a standard tank to see if this combo makes the Mrs. happy. So yes, I placed 3/4 PEX onto a PEX/FIP adapter directly onto the hot water nipple of the Marathon tank. The 18 inch copper stub you speak of is needed for gas water heaters, because of the hot flue right next to the pipes. My Marathon set up from the plumber had 2 BrassCraft flexible copper lines from the nipples to 3/4 PEX that runs throughout the house. We have a recirc line, 3/4 PEX not 1/2 for some reason piped to a Grundfos recirc pump that is plumbed into the drain port of the Marathon tank as per Marathon's recommendations. I removed one flexible copper line to connect the hot Marathon port to the cold Giant port. I thought of installing copper stubs with unions on the Marathon tank, but I had left over PEX so I used that instead. So my number 3 question is can I reuse the flexible copper water heater connector if I choose, or is the crushed copper ring next to the rubber washer a one time only item? If so, are these copper rings available separately? Thanks.

"SparkingWater" thanks for your photo link. This seems to be a photo of the Rehau fittings that prompted my post. Here is more about it, but perhaps not a definitive link: http://www.youtube.com/watch?v=nf9kut6mBdc I am learning that these Rehau fittings are having problems with "zinc-ification" and have had to be replaced. Again, here is a link that may not be definitive, but at least explains the problem: http://www.repipenevada.com/kitec_rehau.html. If it is not one thing it is another. As an alternative, it seems that for connector fittings the Wirsbo, now Uponor is the system of choice these days for PEX (at least from my limited interviews here in Seattle). Who knows down the road what will happen. Here's more information about Uponor: http://www.uponor-usa.com/en/Header/Systems/Plumbing/Homeowner/Overview.aspx here is an interesting link from apparently an inspector's view: http://inspectapedia.com/plumbing/Plastic_Pipes.htm. I do have concerns about long term health exposure using PEX. I hope someone can point me to more recent data, but here is an analysis which reports that PEX likely leaches substances harmful in drinking water, including BPA, but the issue has not been fully studied: http://www.documents.dgs.ca.gov/bsc/pex/exhibit_a_reid_pex.pdf No filtration system seems to be able to filter out BPA. So, although PEX is approved in CA building codes, the issue of safety in drinking water was not fully vetted (perhaps a lawsuit addressed this issue, but I have not researched that). (Are Upanor fittings made in Germany so no BPA?? Is that a crazy assumption?) I think the gist of the message on this discussion link is "go with copper". Oh boy, that I could! I will go ahead and get a quote for copper, but I bet it will really blow our budget. Still, I have young children and I do not want my choice on plumbing to put them at any risk, knowing that perhaps at this point the risks have not been fully evaluated yet. Of course, the issue that really started this thread for me was reliability of PEX fittings... Here is a link that might be useful: BPA in PEX?

Are the pex to copper fitting soldered? It is probably flux residue. It is self limiting, once the reaction uses up the flux salts it stops. If you want to wipe it off it should not occur again (depending on how well you actually clean it off).

I am sure that some people will take exception to my response here but I am in agreement with you, IF IT AIN'T BROKE, DON'T FIX IT. Your house was constructed in 1993, which was at the height of the Polybutylene controversy and you can rest assured that any reputable plumber or plumbing inspector working with PB pipe at the time was staying right on top of the problems. The problems associated with PB pipe were not problems with the pipe itself, but rather it was problems with the fittings. In fact, although the UPC(Uniform Plumbing Code) has banned the use of PB pipe, the IRC(International Residential Code) still lists PB pipe as an approved material for both supply & distribution piping. Principally there was two problems associated with PB failure. PB pipe was run in exactly the same manner as PEX however originally they used plastic crimp rings which had a tendency to blow out from water hammer or they were literally pulled out from thermal linear contraction of the pipe. They then changed to plastic fittings with copper crimp rings, however it was soon discovered that there was a problem with the plastic used to make the fittings. The sidewalls of the fittings were eroding through from the inside out as a result of the friction of the water, especially where the lines were improperly downsized and the velocity of flow exceeded the recommendations. (In almost all cases where we saw PB system failures we found elbows with holes often as large as 3/8" through the sidewall of a fitting.) In fact, many of the code requirements for running PEX are principally based upon lessons learned from PB pipe. Typically the problems with PB pipe began to show up about 3 to 5 years after the initial installation however your PB has now lasted 14 years without incident. Based upon that fact alone, i would assume that you have the upgraded 2nd generation fittings and your risk is minimal therefore it would be prudent to weigh the risk of liability against the cost in time, money and invasive installation techniques before we arbitrarily decide to change it out. As you stated, your shower walls will be open so I would say by all means seize this opportunity to address that section. There is an easy method of changing out the lines to the lavatories if you so desire. Rather than tear out the PB then attempt to jam the PEX in, you can take a short nipple of copper and using the PEX crimp rings you can make a short Butt joint between the two pipes. You then have a helper carefully feed the PEX in as you pull the PB out and it will go through rather easily. For the remaining pipe in the crawl space, even if it fails there is little to no risk of property damage so I would say you could disregard any further changes.