Long plumbing run - pull out copper for pex replacement?
 

While I have my office wall open I have access to the adjacent wall with my plumbing in it. I was thinking about possibly pulling the copper lines out and replacing them with PEX. The reasoning behind it is that I believe that it is a 3/4" copper line running upstairs to my bathroom. It is a full bath with shower stall, sink and toilet. However, 3/4" is overkill for that and it takes a while to get warm water up there. If I were to replace it I was going to think about downsizing the plumbing run. So, I would have a double benefit of the more insulated PEX tubing and smaller diameter to get hot water there faster.

What do you guys think?

I would do it for the hot water line for sure! then insulate it with as thick of insulation as you can get.
I have no problem filling my bath tub off a 1/2" pex line that is over 30 feet long, it also cut the time it takes to get hot water to the shower by half.

You insulate the PEX too eh? I suppose that makes sense. Just seems like jumping from copper to PEX alone would be a huge jump in heat loss alone.

You can never have to much insulation.
One store near here sells some of the thinner pipe insulation for $1 for a 6 foot chunk, $5 and your hot water is insulated the whole way.

Just remember that if your lines run through un-conditioned space (I doubt yours would), it should never be insulated. The space should be insulated to the outside of the piping. we have had many people with insulated piping NEAR a freezing area and the piping burst because it could not get warmth from the room, however little it was.

If the distance is not too, too far and you don't use the bath much, you could try 3/8" tubing which is fine for a low flow shower. The bath might just take a little longer to fill but there would be hot water savings (but not as much as going from 3/4" to 1/2".)

I ended up picking up some 1/2" pex. I contemplated teeing off to 3/8" line to go to sink/shower, but I figured those runs were so short it probably wouldn't make a huge difference.

I'll be showing the work done in my thread about the office remodel here:
http://ecorenovator.org/forum/renova...html#post25613

skip the hot water :) no additional cost, and it will force less water use.

From my plumbing classes.... the 3/4" is to provide sufficient volume for multiple points to be in use without suffering a significant pressure drop. Copper also is anti microbial and therefore is a health +. Pex is plastic and at best is health neutral. Pex is easy to run, if the shower is the only place you care about hot water, just do a run to that and leave the copper to the rest of the bathroom.

Whats the projected ROI of this project? how many years to pay back the cost and time?

I did some rough calculations on pressure drop and switching to the 1/2" is going to increase the pressure drop by probably 2 psi. Nothing big at all. The flow rates are so low that is just isn't an issue.

For the record I probably replaced about 20ft of 3/4" copper with 1/2" pex. I timed things before and after. It used to take 50-55 seconds to get hot water upstairs. Now it takes 20-25s. So, it has been more than halfed. This makes sense because 1/2" PEX has under half the capacity as 3/4" copper pipe. In a 20ft length we're looking at .45 gallons for 3/4" vs .18 gallons for the 1/2" PEX.

Another side benefit is that I can now set my water heater to a lower temperature because the PEX (which I did insulate) is loosng less heat than the copper did. It used to be set to 140F, and now it is set at 130F. It is an on demand electric water heater and has a regulated output temperature.

I know 130F still sounds high, but I also found out this weekend while doing the plumbing that my shower head mixes in quite a bit of cold water on 'full hot'. So, I'll be looking into fixing that as well. Then I should be able to turn it down further.

I have no idea about the ROI. It was worth it alone just to not have to wait as long for hot water. I'm sure the payback will be many years out there. The cost wasn't that great either, probably $25 in tubing and fittings.

Just wanted to give a quick update on this. Its been about a month now using it and it is great having hot water much faster than before. Pressure drop hasn't been an issue at all.

I tried to read into the disadvantages to going with the smallest pipe for the flow rate that I want and kept reading about water hammer because the water is traveling at a faster rate down the pipe. If you shut off the water quick, do you notice additional hydraulic noise?