Hi, folks.... I am renovating a 70 year old home and have decided to replace the old copper with Pex since I have the walls open. Having a plumber do all of the work is just not in the budget so I thought I would try to run some of the supply lines myself and then bring in the pros to replace the stack, take care of the connections and make sure everything is working properly.

Rather than use the Home-Run system where each fixture would have it's own dedicated supply line, I would prefer to run some main supply lines and then branch them off. This would allow me to use the 24 port Manabloc manifold rather than the 36 port version.

For example, in the basement, I would have one cold supply line that would branch off to the two outside spigots and the basement utility sink. One Cold and one Hot line would supply the basement half bath and bar sink. Similarly, I would run one cold line and one hot line to the guest bath and have them branch off (Cold would branch to toilet, sink and shower and Hot would branch to sink and shower). There are some fixtures to which I would have dedicated lines (Washing machine and Master bathroom shower for example)

So...a few question.

First of all, does this make sense?

Second, would 1/2" lines be sufficient for the main lines or should I go with 3/4" and then branch off to 1/2" (Can I use 1/2" from the manifold to the guest bath and then branch it, or should I use 3/4" to the guest bath and then branch to 1/2"?

Finally, if I ran 1/2" lines to the master bath shower and then bumped that up to 3/4" leading to the shower heads, will that give me more volume? This is how the old copper pipes were configured.

In case it helps, this house has 2 Full (second floor) and 2 half baths (first floor and basement). There are only two of us in the house so it's not like there will be a lot of competition for the water.

Thanks in advance for any feedback you can provide.

TC

By code you can only feed 2 fixtures with 1/2. That usually means running 3/4" to the bath and using a 3/4 X 3/4 X 1/2 tee at the next to last fixture. Increasing the pipe size at the shower will have no affect on the volume or pressure at the shower.
I would run a 1" supply with 3/4" mains to each bath.

Is there anything wrong with the copper? Unless the pH of your water is too far off of 7 it may be just fine.

If you are going to re-pipe, you would do a calculation based on water pressure, number of fixtures (and what type) and developed length of piping.