Hi everyone!

I am in the process of removing the soffit in my kitchen to install taller cabinets.

I removed the drywall and found a lot of stuff. I am trying to reroute the water copper pipe through the studs and header to hide it and be able to remove the soffit. Currently, I am only dealing with the water pipes, not discussing the electrical conduits.

Please see below. The main water line is 3/4 in. copper, and splits in 2 1/2 inch copper branches. However, you can see how the wall has a double header, and has two pvc lines running through the header in the back. It doesn't seem to be carrying any load from the joists in that particular location.


To minimize the borings to be done, I thought of drilling through the header that is in front of the pvc pipes. This solution would limit the borings to roughly two 3/4 in bores to run the 1/2 in lines up, and another two 3/4 in bores through the stud to continue the branch to the right.
This would be ideal, since this would mean a single, straight line up to the line that feeds the second floor (which would also reduce the number of elbows needed, and hence the pressure drop in the line)
Below you can see the same area, from a different angle, where the adjacent stud space can be seen (which is empty-ish). Below, there is a picture of the stud space adjacent to the messy one.


The alternative to what I have explained so far is to turn the 3/4 inch pipe into the open stud space, and bring the pipes up through the header into the joist space. However, this requires quite a few elbows, and I am afraid this is going to translate into a significant water pressure loss. So far we have decent pressure but I am unsure of how is this going to affect the result.
Below is the third stud space, the most crowded, but I think the best is to bring the pipes down (basically where they are) but closer to the ventilation duct and do the connection there, avoiding the duct.

So bottom line, I am here to borrow some of your expertise. Can you guys answer the following questions?

1) What do you think is best? Drill up with a straight shot or move the pipe to the open space and do the second, more convoluted solution?

2) I personally prefer copper pipes (not afraid of soldering), but if you think I should change something of my reasoning (such as going with PEX or similar), I can consider that as well.

I really appreciate all your suggestions and help with this issue.

Thank you!

 

Drilling through the header isn't a big deal, so I would plan it out as to what makes it easiest piping-wise. No issue going up through the header and across the studs with the holes for the 3/4" pipe.

I would definitely stick with copper. I don't mind other piping methods, but I wouldn't switch mid-run as it's a hokey fix. Still likely code-compliant, but I'd rather keep it all copper.

I would also add metal nailing plates. Especially with cabinets going in, and possibly using longer screws, you definitely don't want to accidentally hit a pipe!

 

So after a few days, I did do what was discussed. Below is a picture of the result:


(side note, just realized I don't have an actual picture of the finished system; the pipes on the right are also connected)

Everything looked good, and after testing a couple times and fixing minor leaks, me and my wife took a shower to test the new system... and we noticed a quite sharp reduction in water pressure.

I am a bit confused, since the inlet is at the same elevation and the outlets are at the same elevation as well (nothing changed downstream). Only reason I think this could be due to is to the change in pipe diameter from 3/4 inch to 1/2 inch significantly lower than it was before.

My fluid mechanics skills are slightly rusted (I took some classes many, many years ago), but I suspect the main cause could be due to the reduction of diameter, causing an increase of water velocity, which causes a sharp reduction in pressure (Venturi effect). Since the head losses are also a function of the flow velocity, the higher velocity would cause a further drop in head, which translates into a significant pressure loss at the top (where the outlet is).

I have checked and there are no leaks. Just the drop in pressure.

I am thinking of redoing the piping branch causing the issue. For this, I am thinking perhaps to extend the 3/4 inch segment until it crosses the header and reduce the diameter up there (i.e., continue the 3/4 inch branch and reduce the diameter at the very end, instead of mid span as it is now). Where the branch is, I would have a tee with both inlet and vertical outlet of 3/4 inch, and the side branch of 1/2 inch.

Can you guys take a look? What do you think? Any suggestion to fix the issue?

Any help would be greatly appreciated!

 

Looks nice.

I'm surprised about the loss of water pressure. There's of course a loss of volume with 1/2" pipe vs 3/4", but with most residential fixtures, you'll never notice the difference.

I would suggest removing the showerhead and checking the sediment filter. After plumbing work, they tend to get gunked up. Do you notice any difference at your bathroom faucets? Lastly, is it a standard type of shower head? Most showerheads are flow-limited to 2.5gpm, though there are some rain heads that don't follow that regulation.

 

I can be a geek sometimes, so I pulled my book from fluid mechanics from my times of engineering school.

After crunching some numbers, I came up with the losses in the pipe. Changing about 32 inches of the stand pipe (originally 3/4 inch, now 1/2 inch), for the same flow rate (I ran the calcs at the 2.5 gallon regulation), I came up with losses equivalent to 0.125 psi per inch of pipe for the 3/4 inch pipe, vs. 0.87 psi per inch for the 1/2 inch (7 times higher!). If this is applied to 32 inches of standpipe at the rated flow, translates into almost 30 psi of pressure drop just in friction!

Long story short, I am going to redo the standpipe and convert it to 3/4 inch to reduce losses. That should make up for the difference. I will post a picture once it is done.

Thank you for your advice!

 

Zorfdt,

Yes, I noted a drop in pressure in the faucet as well. Since the flow there is significantly less, the drop in pressure is significantly less too, but you can tell how it also dropped. In this case, the diameter was kept the same, but the length was increased by roughly the same 32 inches.

I am estimating that the pressure there should go back to normal as well if I just change a portion of the pipe back to 3/4 inches.

Thanks for your help!