I am having copper rerouted due to a slab leak. The plumber proposes tapping into the 3/4 running through the ceiling to one side of this two story house. This was done years ago due to another slab leak. I call that circuit 1.

Now the circuit feeding the side of the house nearer the hot water tank, located in the adjacent garage, has a hot water leak. I call this circuit 2. The plumber's recommended fix is to abandon the 3/4 copper feeding circuit 2 with hot water (cut the pipe where it comes out of the slab on both ends and cap it), and feed that part of the house by tapping into the line feeding circuit 1 and connecting that line to feed the 1/2 inch feeding a sink.

Is that a good idea? My thinking is backfeeding the this way will cut water pressure/volume to the rest of circuit 2.

I would add that the cold 3/4" coming up into that side of the house is inside the perimeter wall and located about 15 feet from the hot 3/4 shown in center of picture 3. A pair of 1/2" pipes also emerge from the wall at the point where the cold 3/4 comes up.

Picture one is of the 1" coming out of the slag that feeds the water heater tank, as well as circuit 1's abandoned hot and cold 3/4 . The other two pieces of 3/4 being the hot and cold for circuit 2.

Picture 2 is where the plumber proposes to tap into the 1/2 inch. This is taken about 5 feet above the taps for the washing machine. When I look at that picture, it almost looks like the 1/2 comes off of 3/4, but I suppose it is wishful thinking. It is hard to see from a distance as a large cabinet is in the way. I will cut into the wall below for a better view, but assume it is all 1/2". (I got a better look and it is all 1/2")

Picture 3 shows where the existing (probably leaking) 3/4 emerges from the slab below the laundry taps, along with for 1/2 inch. Two of the those four tap off of the other hot and cold pipes up a few feet up and in that wall.

 

The idea is to use the largest size pipe you can to reduce pressure drop but how much of the house do you want to rip apart ?

 

You answered my question, Pjmax. I will make some carefully positioned inspection holes to see how difficult it would be to connect up with that 3/4' copper.

 

I see many houses that were re-piped. What the plumber proposes sounds good to me.
You have a manifold and that's a good starting point, no matter where you want to take it.
That's just my opinion on what I've seen. Around here you are talking $5-8K and they want to make it as easy as possible.
I see no problem teeing off. For example my house has one 1/2" pipe coming in, no manifold and branches out. You're doing pretty good IMO.

 

Handyone (Brian)

Thanks. I guess I am getting a pretty good deal and will give this guy the go ahead if he can explain why an option at an additional charge is to run another 1/2" to the upstairs lavatory. I think, but will ask him, if that is since the single hot line he is tapping into can't carry enough water to keep pressure up when a lot is running. If so, why not just drop down and connect to the 3/4 below the laundry tap? Perhaps he wants to spare me opening up the space between the studs so he has room to feed pipe up the wall and sweat into the existing 3/4.

As for the manifold, all we have is what is shown in the pic 1 and the plumber spent a good amount of time trying to locate another manifold. I think of it as a sub panel for a electrical breaker box, but found none. Basically, there is nothing else and its just copper running will nilly under the slab.

As for costs, the prices you mentioned are pretty much what I paid, adjusted for 15 years of inflation, to reroute both the cold and the hot to the other side of the house. He may be cutting me slack since he worked as a sub on a kitchen remodel last year and I am doing the donkey work on this job so he doesn't have to have an assistant. (Mainly cutting drywall.)

Besides, I would like to replace the broken plastic Oatey recessed plumbing box for the washing machine. Perhaps with a metal box. If so, I guess I could use a shark tooth box, but I open that inter stud space to connect 3/4 to 3/4 then won't it be easier to replace that plumbing box?

Here is a picture of what I mean, which is essentially to take the opening a few inches up from the floor all the way to the top of the plumbing box. The opening shown in pic 3 above is at the bottom of that wall chase into which the plumbing box is recessed.

 

The plumber flaked off on me, even when I opted for the most expensive solution. Why he didn't say and I expect he realized I wasn't going to let him charge me $5,000 for a job he estimated to cost $2,500, when he was panning to take every possible shortcut and delivering a $1,250 job. I have another licensed plumber coming buy tomorrow to take a look at dong the job. This guy is busy and referred over by my Optometrist so he should be good.