Tee off 3/4" or 1/2" off manifold

[Djarchow]

Finishing my basement. We are under the 2015 UPC. I will have a bathroom with shower, vanity, and WC. Bar area will have a bar sink and a dishwasher. All will be used intermittently. My existing copper manifold hot and cold sides only have one 3/4" connection each and that supplies the master bath so if I used the 3/4" to supply the new fixtures I would have to tee off the existing lines. I have an unused 1/2" connection in the existing manifold for both hot and cold.

Each fixture will have it's own homerun back to new 6 port copper tees/manifolds which will be located by the main manifold. The new tee takes a 3/4" sweat connection so I could use a 3/4" or 1/2" fitting. The bathroom runs would be about 70 feet, the bar is about 15 feet. Our water pressure is around 45-50 psi. Looking at the UPC tables, I would have 4.5 fixture units for hot and 5.5 for cold so 1/2" appears to work for all the branch runs.

To meet code and get decent performance should I tee off the exiting 3/4" lines for the new tee/manifolds or use the open 1/2" connections?

Thanks in advance for your help.

 

[Reach4]

To meet code and get decent performance should I tee off the exiting 3/4" lines for the new tee/manifolds or use the open 1/2" connections?

1/2. I am not a plumber.

 

[Sponsor]

 

[Jadnashua]

You don't want to feed more than two items with a single 1/2" run/port for best performance. FWIW, according the the Copper Institute's guidelines, you do not want a higher flow rate than 5fps in a copper pipe for the hot line (a bit more on the cold), which on 1/2" equates to about 4gpm. A typical shower head is limited to 2.5gpm, a vanity the same, and a toilet is volume limited, not flow rate, but because the line to it is usually smaller, probably not more than a couple of gpm or so.

So, depends. The outlet of the shower and vanity will be a mix most of the time of hot and cold, but in the winter, it could be mostly hot since the cold will be so cold.

 

[Djarchow]

Reach, Jim,

Thanks for the replies. I appreciate it. So we have one vote for 1/2" and one 1/2" maybe. Just to clarify, the only place I see the bottleneck for the 1/2" is the 2' run between the main manifold and the 6 port tees that will feed the new fixtures. Since this is for the basement, the bathroom will be used much less frequently than the bathrooms upstairs, and then mostly just the toilet and vanity. The shower will get used even less. Same with the bar sink, and dishwasher.

Thanks again for all the feedback.