DWV insert pipe into run

Question

I would like to insert some short lengths of 3" copper into a DWV main line that is made of PVC. I will be wrapping soft copper around these short lengths and running the cold water feed for the shower through the soft copper to capture heat from the drain water.

My question is for you plumbers, what procedure would you use to insert a fitting or Tee into an existing run?

After I cut it, I can probably move the line an inch or so fairly easily but any more will be more complicated but can be accomplished.

Edit: I should add that the shower drain is too tight to the main line to put the heat exchanger in the 2" shower line.

If I wanted to add a Y into the main line and move the shower drain I would still have to cut the DWV and insert the Y. How do you guys cut in to an existing line to add a fitting? Do you use rubber couplings?

Would something like this be reliable for decades to come?

http://www.zoro.com/fernco-flexible-coupling-4-in-l-3-x-3-in-1059-33/i/G2880026/?gclid=CNXrp8jcn8kCFYRDaQodd-AM-Q&gclsrc=aw.ds

Answer 1

Rubber adapter couplings are what is used for what you want to do. You will need to insure that you order the correct one as copper and PVC have different outside diameters.

I do not think that you will get good heat transfer by simply wrapping soft copper around the drain line as there will be minimum contact. There are commercially available products on the market that do what you are looking for that will provide much better heat transfer. Here is one such product: Recoh-vert.

You'll notice that the pipe-in pipe method archives much greater contact between the hot drain water and the incoming cold water. They also install these on the vertical as what travels around the inside wall of the pipe when draining vertical (as opposed to just the bottom when draining horizontally). This also increases the amount of heat transfer.

You can make a similar product yourself, though I question the possibility that a home made product would prevent cross-contamination. Defiantly would not pass any local codes. Here's a video on how to make one: Shower Heat Exchanger.

If I understand your situation, you have limited space in install the heat exchanger. I believe that there are also p-trap versions available.

Answer 2

No pipe movement is needed if you use repair couplings. These are couplings with no internal stops.

The procedure is thus:

• solder a short length of pipe into both running legs of the tee
• measure assembly length and remove a slightly longer section of the pipe in question
• place a repair coupling onto both cut ends of the pipe and slide them back out of the way
• place the tee assembly into the cut area and slide the repair couplings back to cover the two joints. Ensure the couplings are centered on the cut and the tee assembly is oriented properly (I use various tools and such to prop the assembly and hold it in place)
• solder the repair couplings into place (I use wet rags to wrap existing solder joins, to prevent them from softening)

Of course, all fittings and pipe are prepared properly (deburred/reamed, cleaned shiny, etc.)