Use a main trunk line or manifold with seperate lines with Pex?

I am remodeling my master bath to start with and want to redo the copper plumbing in the entire house as I go along. I want to use Pex for it's ease and cost. I cannot decide if I want to run two main trunk lines for hot and cold and branch off to supply's or use a manifold and run individual lines to supply's.

It seems using a trunk line would be cheaper in the beginning but not sure in the long run. I was thinking of 1" trunk lines branching to 1/2" to supply's.

What is every ones census?

skeeter

 

if your pipe from your meter is 3/4 " I would stay with 3/4" main lines then reduce to 1/2 " for each branch (raiser). That way you maintain flow and pressure to each fixture( ie sink, toilet , shower, washing machine , etc) Also be sure to install a shut off valve on each branch for ease of isolating as needed. I use the theory that you can not have too many shut off valves. I know in reality you can,but most times there are very few used when houses are built. Make sure that you use ball valves.

 

I think it's best to answer that on a case-by-case basis. Add up the cost of the many fittings in a branch vs. a "home run" plan. Also consider whether you have straight-line runs between joists or across. I wouldn't do a home-run layout if it required drilling 8 holes in every joist, for example.

 

I used a hybrid approach when I did my house. I have Kitchen, laundry, guest bath, and slop sink all near each other, and two bathrooms at the other end of the house. I put a valved manifold near the kitchen group and one near the bathroom group, running 1" PEX to supply the manifolds. I think it was a good compromise. I think there are less than 10 fittings (elbows, tees, etc) in the whole system. One downside is that first person to shower in the morning has to wait a long time for that 1" pex to fill with hot water. But it wouldn't be any better with a main line approach; first use still has to fill it up. Perhaps some day I'll put in a recirc system.

 

I just redid my whole house with pex. I was going to do a home-run manifold but decided against it. I used 3/4 from the main to the water heater and then ran 3/4 hot and cold under every room that would need plumbing (trunk and branch). I just used 3 port copper manifolds under the bathroom and kitchen. Each fixture in the house has its own 1/2 line back to the 3/4 line. I'm glad I didn't use the home run manifold--that would have taken forever and a lot of 1/2 pex. Insulating all those hot 1/2 home run lines would suck. I have no issues with flow rate when multiple fixtures are being used.

 

I have decided to go with using a main trunk line. Initial cost would be a lot less even with branching and using individual supply shutoff valves. And I hadn't even considered the cost and labor to insulate all those 1/2" hot lines on a manifold system.

I was going to also go with 1" main line because I worry of pressure drop with multiple items being used at the same time. You know, the flush the toilet, scream from the shower problem that I now have. Would 3/4" be sufficient to not have this problem. My water pressure is around 60psi.

skeeter

 

Using a 1" main may help, but the answer to "flush the toilet, scream from the shower" is a pressure balanced shower valve.

If you're going the main trunk route I'd probably use 1". Doesn't cost that much more, and since you'll have a lot of Tees and other fittings, all of which impede flow, upsizing probably makes sense.

 

If you are on a slab, running new lines as you go along is a good idea. A slab leak in CA is close to guaranteed.
Have you thought about eventually bypassing all lines that are under the slab?

 

I do plan on bypassing all the lines as the remodel jobs are done. The copper in the slab are 40yrs old and all you have to do is look at them and they leak. I've repaired quite a few and just hate them.

 

So the shower balancing valve is that something built into the shower valve or is it a separate unit?

 

The pressure balancing feature is built in to the shower valve, so you would have to replace yours to get it. If it senses a reduction in, say, cold water pressure because someone flushed, it instantaneously reduces the hot water flow to match. So you may get a temporary reduction of flow out of the shower head, but the water won't go scalding hot.