PEX Home Run diameter

[spurlockda]

Need a little education please. Running new PEX throughout and I wanted to run 3/4 runs to the various fixture locations. I was chatting with a plumber and his opinion was that since you tapped into the various fixtures with 1/2", it was a waste of time to run anything other than 1/2".

I probably know enough hydraulics to be dangerous and when I started thinking about it, he seemed to be making sense? I know that at a given pressure you deliver a greater volume with larger pipe. And, when you neck down in diameter while retaining the given pressure, you just increase velocity? That's when my science breaks down.

So what is the best way to do this? I'd like to have good pressure with good volume at the second story showers and sinks. I know the toilets are good ay 1/2. Would it be helpful to run 3/4" to showers and faucets?

Thanks,
Dave

 

[Dj2]

Listen to your plumber, he's correct.

 

[Sponsor]

 

[Reach4]

Smaller diameter pipe for your hot will give hot water sooner.

 

[DaveHo]

1/2" is plenty big if you are doing home runs from a manifold. I would consider doing 3/8" for the hots to faucets if the runs are long. The newer flow restricted faucets can take a long time to get hot water.

 

[Jadnashua]

It depends a lot on how many fixtures you want to run at any one time. Keep in mind that at the maximum flow rate of 5fps, 1/2" PEX only passes 4gpm. You can use slightly faster flow rates with cold water, but for longevity and sound purposes, you should limit the max flow to those values. 4gpm is fine for a showerhead, but throw anything else on that supply line and you might start to notice loss of pressure and volume, especially if one of those fixtures was a tub. 3/4" PEX has about double the volume at the same flow rate. Yes, through a SHORT section of pipe, the flow rate increases if you neck it down, BUT, it also experiences increased friction, and that, over distance will limit things. One study I read indicated that the use of a properly integrated hot water recirculation system ended up saving overall energy verses the costs of water, heating it, and sewer costs without. Regardless, it is much more convenient to have it verses not having it.

If I was going to go with a manifold system, I'd want to run at least 3/4" to it, and you could choose either 1/2" or maybe 3/8" out, depending on what you're feeding from it.

 

[spurlockda]

Thanks Jim,

I appreciate the detailed response. That worked best to educate me.

I'm shopping for a water recirc system (I need to automate it to a degree. It's my Mom's house and she's 90.). Sometimes when I visited in the past she would forget I was taking a shower and flush a toilet or start the dishwasher.

I'm also researching a remote vent system to automate the bathroom vents, the kitchen vents and the basement vents. (Same reason as before. Unfortunately remembering to turn things on or off are bygone days.)

I'm going with the toilets in Terry's toilet thread. I saw one out there that somehow limited overflows which would help possibly. I've water-tightened her new bathroom with Schluter systems and I'm putting in a low point drain so that if she floods the toilet or sink, it will be contained within the Schluter envelope.

Again, thanks for everyone's help but keep coming with ideas and suggestions.

 

[spurlockda]

Listen to your plumber, he's correct.

Thanks.

 

[Jadnashua]

Some of the Panasonic vents have built-in humidity controls, and, they have a company that makes wall switches that perform a similar function. This isn't really humidity, it relies on condensation, so it's best to have it built into the fan, since it is likely to start condensing there verses the walls first. But, it does work. I installed one at my mother's house in the bathroom guests normally use, since they would be less likely to think about turning on the fan to help things out. You can still manually turn the fan on/off at the wall, but if you turn it on, it will run for a period of time, then turn itself off after a delay (unless there's condensation, then it will stay on plus a delay). So, especially since the Panasonic stuff is so quiet, that's good, otherwise, it might end up staying on for much longer than required until someone realizes it is on.

I have a SolaTube tubular skylight with the optional light and fan. There are a few companies that make these things, but SolaTube is the first, and I think, still the best. The 10" diameter one on a sunny day, provides the light output of about a 300W lightbulb. It took me a year to get to the point I didn't' try to turn the switch off when leaving the bathroom. On a snowy night, the white roof and the outside lighting causes enough glow in that bathroom such that you can see enough to get around. Really neat products.

From a multiple unit, centralized fan system, look into FanTech products.

 

[hj]

Start with the fact that no matter HOW large your piping is, the SMALL opening in the faucet will determine how much volume you get.

 

[spurlockda]

HJ,

KaBam, you hit it perfectly - that fact is what is making my head hurt. It seems strange that no matter what size pipe you run to the fixture you get necked down by the fixtures. That is the root of my confusion. At a given pressure, I want to maximize the amount of water that is delivered to the person in the shower to have an enjoyable experience - even if it involves having a rain shower coming down on your head while a shower head (or two) gives you an invigorating spray.

I understand that the "flow" (volume and pressure) to the toilet is not complicated. I think I understand how the vanity sink is relatively uncomplicated in terms of the "flow" in that the volume and pressure doesn't need much customizing.

I'm assuming that if I have the shower individually plumbed directly from the manifold, turning on the dishwasher or whatever won't result in a cold/hot surprise.

 

[Jadnashua]

The venturi effect is what causes a fluid to speed up through a small obstruction - this works with both gasses and liquids. If the obstruction is small in length, you may not notice any overall flow reduction depending on exactly how small that orifice is. It is when the length after the obstruction remains smaller that the increased velocity causes more friction, and thus reduces the flow.

 

[Reach4]

Some showerheads have devices to limit the flow. These devices are not simple restrictions, but specially designed devices to maintain a design flow over a range of incoming pressures. Using 1/2 vs 3/4 inch on those will probably make little difference in the flow. Some people have figured out how to make modifications to some of these showerheads to defeat that design.

It is also possible that the restriction is in the in-the-wall shower control.

http://contractormag.com/columns/editorial/policing-showerhead-outlaws-0410

Similarly, your lav spout may have such a flow control-- usually built into the aerator. http://www.neoperl.net/en/oem/products/aerators/pressurecompensating.html

 

[Jadnashua]

ONe thing you might want to look at is the rated gpm flow rate of the valves you are considering. Those all assume 1/2" copper inputs and around 60psi static pressure (well, unless it has 3/4" or larger inputs!). Pex at 1/2" will be smaller than that 1/2" copper, and could limit that flow. This is typically only important if you are filling a tub, verses taking a shower. Only a few things in a home typically do not have intentional flow restrictions in them: tub filler valves and outside hose bibs...in general, those can use as much volume as is possible from the supply line. All typical vanity or kitchen sink valves are flow restricted, as are shower heads. But, decide on multiple shower heads and maybe some body sprays, and you can use all of the volume possible (and a big water heater, too!). IT gets more complicated when multiple devices are turned on at the same time...then, depending on how things are plumbed, it can become a major performance issue. Modern pressure balanced shower valves help prevent getting scalded or a cold spike, but it's better to build the supply lines well to minimize that in the first place.