Shady plumber or paranoid client?

[Daniel S]

I need some plumbing work done in my house and called around a few plumbers. Amongst other things, I need to replace my water heater, add an exterior run and add a dishwasher run. I also have a low pressure issue in my bath/ shower. I have PEX supply lines throughout the house.

So my conversation with the first plumber was going great until I mentioned the low pressure problem and my desire to install a Manabloc manifold with a home run system. The current branch and tee set up is awful (bends, elbows, tees and couplings everywhere). As my main water supply line is only 1/2", the guy immediately suggested thousands of dollars worth of work digging up my yard and under the my foundations to install a larger 3/4" main water supply line. So I went from suggesting a manifold and home run system to him giving me a quote for $4,700.00 and that isn't even touching the things I was calling him for to begin with.

My rationale is this; I have excellent water pressure everywhere in the house except for my washing machine and bath/shower and it really isn't that big a deal. My vanities and exterior hose pressure is strong it just takes a long time to fill the bath; it is a soaker tub.

Am I right to think this doesn't sound right? I mean, if my main water line was aneamic, wouldn't all my fixtures have low water pressure? Would a manabloc and home run system really be a "waste of time and money" as this guy is saying or is he trying to give me the shaft? I can admit that I am sceptical but something just isn't adding up here. I really want to go with the manifold to clean up the current PEX "spaghetti fest" that is my current supply system. Is my solution a bandaid fix or something that I should do regardless of my supply line shortcomings?


Confused Daniel

[geniescience]

I need some plumbing work done in my house .... also have a low pressure issue in my bath/ shower. ....

go ahead. Your thinking is clear. You currently have Pex in a branch and tee set up with bends (elbows and tees) "and couplings everywhere".

Use a 3/4" home run for your soaker tub. You can use that size everywhere else too; it does help.

There is a maximum flow possible from a 1/2" pipe (or any pipe), but your plan is initially to let the water enter the house and reduce further friction losses after that point. Sounds like a plan!

Then, later, independently, you can increase the entry pipe size if you want even more. You may be fine without; you'll know when you're finished Step 1. Here is a trick question you can ask that plumber and others: what is the difference in flow, if you have a pipe made of two parts of two different diameters, when you reverse the flow? Does water flow more through the pipe when the bigger diameter is the first part? Or vice versa?

Pex at 1/2" (nominal) is a lot smaller than copper at 1/2" (nominal). Real inside diameter (I.D.) of a 1/2" copper pipe is halfway to the I.D. of a 3/4" Pex pipe, or put the other way around, a 3/4" Pex pipe is nowhere near as big as a 3/4" copper pipe.

I have 3/4" copper coming in, and 1" Pex-Al-Pex indoors.

david

[jadnashua]

First, pressure and volume are different. When all valves are closed, you have the same pressure everywhere. The low volume coming out of the tub could be increased if the hot water temp was increased. This would allow you to use more from the cold side, increasing the flow a little. I don't think changing the system to a bunch of home runs will help much with the volume situation. You might help the simultaneous flow rates a little (i.e, if you have multiple taps open), but won't help filling the tub faster unless you go with larger pipe.

Changing the whole system out to 3/4" or 1" pex, and while you are at it doing the manifold; say 1" main lines, then 3/4" to the larger flow devices and 1/2" to the rest would minimize the friction losses. But, with a 1/2" supply, you won't see a huge increase, I don't think. I could be wrong! See what one of the pros has to say.

Is the incoming pipe copper, galvanized, or something else? If it is galvanized...change the incoming pipe and upgrade the meter to a larger pipe size, then see what things look like inside.

[Cass]

Do you know what the pressure is on the street?

[hj]

A 1/2" main line, if that is what you really have is TOTALLY inadequate for almost any use, and it becomes less adequate the longer the pipe is. Once you have that, it makes little difference whether you use larger pipes, a manifold system, or a tree system with branches, you cannot get more water out than that dinky pipe will supply. Then using PEX sized like it was copper also creates a problem because its i.d. is smaller than copper, and since the reduction is on the outer part of the circle, its effect is dramatic for even a slight reduction in i.d.

I would also have recommended a new main line, 3/4" or 1" depending on the circumstances, before even considering any other modifications.

[geniescience]

What hj said.

...you cannot get more water out than that dinky pipe will supply...

so, from that starting point, you may feel that you can fill a soaker tub fast enough, if everything else is right from that point on.

Daniel, what you suggested in your first post eliminates losses you now have (elbows, couplings, small size, extra distance). It'll be a big improvement. It may be enough.

Using small diameter Pex:

... creates a problem because its i.d. is smaller than copper, and since the reduction is on the outer part of the circle, its effect is dramatic for even a slight reduction in i.d. ...

Once you have done all that, the limiting factors will be pressure (as Cass asked about) and the tub spout itself. Some tub spouts are twice as large inside as others.

david