Re piping a house in pex

[86k10]

I have 60 year old 1/2" galvanized steel water pipes in my house that I am replacing soon. The main part of the house (original) is only 750 sf and is all 1/2" steel the whole pipe. I was thinking about going 3/4" pex all the way throughout due to the ID being about the same.

I am doing trunk and branch due to the limited pipes ran in a small house with 1 bath/kitchen/washer/dryer. I am planning on running the same paths as the steel pipe that is in there once removed.

I notice most people run 3/4" main with 1/2" to fixtures, has anyone ran 3/4" all the way to the fixtures? Any issues with this? I was thinking that most of the reduction is in the sink lines and such.

 

[jdieter]

I just did the same project. 1/2" is much easier to route for branches. I don't see how you'll gain anything with the flow restrictions at any device attached to the piping. However it won't hurt anything except a little bit in the wallet.

 

[jhelrey]

Anything is going to be an improvement at this point for the simple fact is the galvanized piping has prob. closed in on itself a bit.

 

[Whiskyb]

I did my whole house in 3/4" For the cost difference it was a no brainer.

 

[sberry]

I notice most people run 3/4" main with 1/2" to fixtures, has anyone ran 3/4" all the way to the fixtures? Any issues with this? I was thinking that most of the reduction is in the sink lines and such.

Air and water lines suffer from bigger being better and this is true if the system behind it can deliver and you are trying to fill a tank. 3/4 is good to hydrants on the cold side but I use 1/2 on the hot and use T's. There is restriction at devices and more so than ever with lo flow fixtures, the small lines do not hurt yo0ur system but actually help it in that it speeds up hot water delivery. It takes 2x as much and 2x as long and energy savbers make it slower.
The demands on modern piping have not went up but down. Original codes and sizing were designed when water saving didn't matter and you had 5 gallon flush and 5 gpm shower heads. Even as bedrooms went up and second baths became common they didn't increase pipe size.

I did my whole house in 3/4" For the cost difference it was a no brainer.

Its obvious from this forum that this is a common thought. None of the small pipe is effecting delivery when hooked to fixtures, even a common silcock is restrictive and meant to be in most cases. The object here is not to drop system pressure as fast as you can every time one turns the water on. Its designed to let SOME out, not all of it as fast as it can.

 

[CNGsaves]

The 3/4" runs NEED to be in place for high volume locations like water heater and washing machine. Also, have your largest water supply lines for outdoor spigots . . . . nothing worse than low water pressure out there.

Problem with running 3/4" to every sink, toilet, shower . . . . is HIGH water flow that leads to over-use of water. Thus, you may inadvertently begin using more water, just because you can (ie high water flow). If you are paying for expensive city water, this could add up. YMMV

+1 on Sberry comments that too large runs for hot water not helpful.

 

[indyokie]

As another said, getting 1/2 into spots is much easier than 3/4" you could likely bend 1/2 in spots where 3/4 would need a 90.

3/4" for your hot will just end up taking MUCH longer for you to receive hot water from the tank. Years ago I did a Manablock feeding 3/8 Pex to a friends house, his old galv pipe got hot water to his tub in 1-1/2 min. With 3/8" pex it was 30 seconds.

 

[acer66]

The 3/4" runs NEED to be in place for high volume locations like water heater and washing machine. Also, have your largest water supply lines for outdoor spigots . . . . nothing worse than low water pressure out there.

Problem with running 3/4" to every sink, toilet, shower . . . . is HIGH water pressure that leads to over-use of water. Thus, you may inadvertently begin using more water, just because you can (ie high water pressure). If you are paying for expensive city water, this could add up. YMMV

+1 on Sberry comments that too large runs for hot water not helpful.

interesting with the washer lines, I just did some plumbing at a house and installed pex washer hook ups and the only ones the big box stores had had 1/2" hook ups.

I obviously also need to do more research on the whole bigger is better thing.
I normally run a 3/4" trunk and branch off with 1/2" which seems not to be the smartest thing to do.
Never worked with a manyfold but if you do mostly homeruns than that makes sense.

 

[acer66]

Oh and the proper crimping tool like the ones from Zurn are their weight worth in gold if you do a bigger project or work more often with pex.

 

[Platonic Solid]

Read and Understand the PEX Design Guide

Edited to change link to 2nd edition.

 

[acer66]

Read and Understand the PEX Design Guide

reading and following instructions?
where is the fun in that?

 

[sberry]

Anything is going to be an improvement at this point for the simple fact is the galvanized piping has prob. closed in on itself a bit.

It can be severe, I have seen 6 inch ******* you couldn't see thru or even poke with a wire and water still goes thru but some minor build up doesn't hurt much except for obsessive compulsive types.
Over 60 years the fixtures have became more restrictive making the piping more efficient for lack of a better term.
I moved in to a place where it was all original and built in early 70's, at first every shower drained the tank and was out of hot. Change the head and never run out, with that and a stool change never notice other users on the system, same pipe.
If I was to replumb a home today with a roll of 1/2 pex and a few t's and put a couple things on at least one circuit especially sinks where frequent hand washing was an issue.
There are places you can do only so much but God didn't usually set the water heater, we often move them. My own is bad and long from kitchen, my Mothers is ideal with about 5 ft of small pipe.

 

[sberry]

interesting with the washer lines, I just did some plumbing at a house and installed pex washer hook ups and the only ones the big box stores had had 1/2" hook ups.

This is because the machine basically only lets in water so fast and the 1/2 is sufficient. Bigger pipe wouldn't speed it up.
I have a large well, I have pipes 1 size up and I fill tanks on occasion qand have it tuned for that. Back in the day they bypassed the system with a run steady well but it really sagged system pressure and one reason was the pipe was too big. Now I have a 3/4 hose with full ports comes off an inch and its perfect. The well runs constant and the system pressure remains at 45. I could put an inch hose on, didn't calculate how much faster the fill would be but but would drop the pressure and maybe not change it much at all. I can stand and watch the gage and tell if someone turns on something else.

 

[CNGsaves]

Other risk of too large runs to toilets . . . . leaks . . . or . . . run on.

A flapper that doesn't seal well on a toilet will just keep running and running burning a hole in your pocket with city water. No need giving higher water pressure to this risk. Also, when the toilet gets clogged, who wants water coming in faster than hell overflowing the whole bathroom floor !!

 

[sberry]

There is a general misconception that bigger is always better, that the code is inadequate and that some minor pressure drop hurts everything. There is also a misconception that every valve is wide open and on at the same time, that every circuit with a 20A breaker is using 20 and we base calculations on this vs the applied load.
It used to take a 1/2 line to feed a toilet now we can put 5 on the same circuit. Went from 4 to 3 waste line and it works better.

 

[sberry]

Water Conservation
Properly designed PEX plumbing systems have the potential to conserve water (see Chapters 5
and 7). The flexibility of PEX allows it to bend around corners and run continuously, reducing the need for fittings; this allows downsizing the pipe diameter to 3/8-inch for certain fixtures.
Home-run systems and 3/8-inch pipes minimize the time it takes hot water to reach the
fixture. Lengthy delivery time for hot water represents a significant waste of water as well as
energy; a problem exacerbated in larger homes.
In 2002, the NAHB Research Center conducted software simulations and laboratory tests on a “typical” hot water system using a trunk and branch rigid pipe design and one that included a 3/8-inch diameter PEX home-run system. Results indicated that systems using shorter 3/8-inch runs with a home-run manifold reduced the wait time for hot water and wasted less water than longer runs of rigid pipe with many elbows and connections.3

 

[sberry]

In the summer latent hot sitting around from short runs in 3/4 add to cooling cost, a double negative.

In service, the use of PEX systems can
reduce energy and water use by delivering water to the fixtures faster and by reducing losses in
the piping.
Energy Efficiency
PEX piping offers reduced heat loss and improved thermal characteristics when compared to metallic pipe. In addition, less energy is used by the water heater because of shorter delivery time for hot water with PEX parallel plumbing systems.

 

[Jackfre]

be careful in your use of fittings. Each fitting is a bushing and reduces performance at the faucet. Rather than the fittings use the radius supports for all of the 90's that you can. I agree that 3/4" to the fixtures is not the best. Also keep in mind that depending upon what you have for a water heater, to large piping will create delay in delivery. 1/2 & 3/4" pipe have a cross sectional area of .19 and .44 sq in. To long a run of 3/4 will have you screaming for hot water as you stand tapping your foot and may lead to a recirc pump on the system. I've seen many recirc systems that were poorly controlled and ended up costing more in heat loss off the piping than the actual hot water cost. "Compact Design" is the concept they are beginning to push for plumbing systems. I repiped my house from 80 yr old galvie in the remodel and for both baths and the kitchen the longest hot water line is 16'. It steps right along.

 

[acer66]

thanks guys, this is a lot of very useful information and shows me again how little I do know.

 

[sberry]

Copied

Comparing the flow pressure and flow rate is a good way to determine the performance of a
plumbing system. The limitation is that the pressure at the base of the riser is dependent on the size of the service line, meter, and water utility supply pressure. In order to describe and compare the performance of each type of system, the pressure drop from the base of the riser to the farthest outlet (including elevation losses) can be evaluated. Figures 8.4 and 8.5
show the comparison of pressure drop based on various outlets in the system flowing with the resultant pressure drop at the farthest fixture. Both figures indicate that the home-run system,
while having a higher pressure drop to the TF, has a more consistent pressure drop during
simultaneous flow. The other systems, based on the trunk line feeding branch lines, continued to show increasing pressure drop as more fixtures were added to the system. In fact, when the full set of fixtures was operating simultaneously, the trunk and branch system pressure drop exceeded that of the home-run and the remote manifold configurations. (The remote manifold
system is highly dependent on the system design, i.e., the location of the manifolds and the
number of fixtures connected to the manifold).

 

[sberry]

Water and time savings of between 30 percent and 40 percent were identified based on this
analysis of the home-run system over either the trunk and branch or remote manifold system designs.


BTW, I see they have 3/8 in this system, I had never really looked at it. I had been considering a smaller like to my main shop sink.

 

[86k10]

Thanks for all the info guys, I am planning to use the Mil3 crimpers. I had to replace about 10 feet of hot pipe after the water heater about 2 years ago and re-did a camper with blown out copper pipes. I bought some 3/4 straight pex at Lowes and need to make another run for some 1/2 now.

 

[Average_Joe]

I ran 3/4 main lines and to my showers only (I like good flow and pressure in the shower) 1/2" branches to everything else. No flow issues at all, using 3/4 branches will unnecessarily complicate connections to fixtures.

Also, make sure you have a "home run" to your water heater.

Keep in mind that new faucets are designed to be low flow, so you may have to remove/modify the diffusers if you want good flow.

 

[W_A_Watson_II]

Problem with running 3/4" to every sink, toilet, shower . . . . is HIGH water pressure that leads to over-use of water. Thus, you may inadvertently begin using more water, just because you can (ie high water pressure). If you are paying for expensive city water, this could add up. YMMV

It's clear you don't understand Flow and Pressure. Pipe size allows more flow and less Pressure Restriction while flowing. When the flow stops the pressure at the consumption point will still be approximately the same. Yes going with a very small pipe like an 1/8" will have a lower pressure at 100 feet from the other supply end when the flow stops, but we are talking 1/2" to 3/4" in 2 to 5 feet lengths from the trunk line.

So a larger pipe to a toilet might allow it to flow faster and let it overshoot the tank level setting before the valve reacts and use a little more water (but flush better), but a larger pipe will not be delivering more pressure and over power the valve.

Most all plumbing devices are designed for 60 psi nominal (80-85 maximum per most codes), while very few homes see that pressure, anomaly we see in the 40 to 50 psi range.

 

[Platonic Solid]

reading and following instructions?
where is the fun in that?

Actually, probably better to Read and Understand the latest edition: Pex Design Guide 2nd Edition

Also, this Fixture Flow Rate Comparison PDF is worth taking a look at.

 

[86k10]

Here is my one issue I need advise on is 15'into the house the main pipe tees off to the bathroom thru the floor then runs thru the wall to the sink, toilet, shower in that order. Would you run 1/2 from the trunk line under the house and branch thru the wall? I will try to draw in the computer later this evening.

 

[acer66]

Actually, probably better to Read and Understand the latest edition: Pex Design Guide 2nd Edition

Also, this Fixture Flow Rate Comparison PDF is worth taking a look at.

wow, not only do you want to have grown man read and understand instructions, now you also want them to use the current version?

does that mean I should ditch my decades long "experience" in trial and error?

 

[CNGsaves]

It's clear you don't understand Flow and Pressure. Pipe size allows more flow and less Pressure Restriction while flowing. When the flow stops the pressure at the consumption point will still be approximately the same. Yes going with a very small pipe like an 1/8" will have a lower pressure at 100 feet from the other supply end when the flow stops, but we are talking 1/2" to 3/4" in 2 to 5 feet lengths from the trunk line.

So a larger pipe to a toilet might allow it to flow faster and let it overshoot the tank level setting before the valve reacts and use a little more water (but flush better), but a larger pipe will not be delivering more pressure and over power the valve.

Most all plumbing devices are designed for 60 psi nominal (80-85 maximum per most codes), while very few homes see that pressure, anomaly we see in the 40 to 50 psi range.

Problem with running 3/4" to every sink, toilet, shower . . . . is HIGH water FLOW that leads to over-use of water. Thus, you may inadvertently begin using more water, just because you can (ie high water flow). If you are paying for expensive city water, this could add up. YMMV

Sorry if my comment set off your PRESSURE / FLOW meter !!

I understand pressure & flow . . . just didn't word that section well. But I'm sure you knew what I meant that 3/4" piping NOT necessary for every sink & toilet and could lead to OVER use of water, that is expensive.

So I . . . fixed it for ya . . . changed couple words from pressure to FLOW !! See blue words above that should make you feel better.

Pro's already chiming in that 3/4" not necessary to everything.

 

[Xicaque]

I am not too impressed with PEX. I have yet to work with it but as of now, I am old school.

 

[W_A_Watson_II]

Here is my one issue I need advise on is 15'into the house the main pipe tees off to the bathroom thru the floor then runs thru the wall to the sink, toilet, shower in that order. Would you run 1/2 from the trunk line under the house and branch thru the wall? I will try to draw in the computer later this evening.

Me, yes I'd run the line in 3/4" to the lat "T", then 1/2" to the last two devices. Most Showers, sinks etc.. that are relatively new have water saving devices that reduce the flow at the final point of use. So supplying the higher rate as close to the use point will reduce pressure drops while water is flowing and make the end user much happier with the water use point.

 

[Platonic Solid]

wow, not only do you want to have grown man read and understand instructions, now you also want them to use the current version?

does that mean I should ditch my decades long "experience" in trial and error?

No amount of guides and plumbing codes will make up for real world experience, but designing a viable system on paper can save you time and money. With that said, want looks great on paper always seems to translate into lots of on-the-fly modifications during installation. Now your decades of experience really come into play.

 

[theoldwizard1]

The 3/4" runs NEED to be in place for high volume locations like water heater and washing machine.

I wish we had run 3/4" all the way to the laundry tub instead of reducing it !

 

[theoldwizard1]

Bends are always a pain with PEX. For tight areas, just go with brass 90° elbows. I know it kind of defeats the benefit of PEX, but it is much easier than fighting.

If you want bent tube, there are 2 things you need to do.

1. Unroll your coil and let it sit in the sun for several hours. You will need some heavy items to weight it down. Hot water works also, but you need a large trough and still can only do a section at a time.
2. Use the PEX corner supports/bracket. Guaranteed no kinks !

 

[CNGsaves]

I wish we had run 3/4" all the way to the laundry tub instead of reducing it !

I've found that same problem with older house I recently bought. Outside spigot on that side of house had 3/4" copper run over there, but they skimped and T'd in washer to already taxed 1/2" copper from nearby bathroom sink. Still finding a few things here & there with copper plumbing that was jerry rigged. One day when list is done, I've got to cut up copper and start making improvements.

 

[acer66]

Since we are on the topic, I now have seen for the first time some plastic connectors for pex for around half the price of the metal version.

Are they any good?

Thanks.

 

[volleyball]

What was mentioned but kinda lost in the discussion. A good way today is to do it with pex is to home run your lines. At least for the hot water. Don't oversize the line and you'll get hot water sooner.

for the OP, a 3/8" line would probably flow more than the galvanized does today

 

[Platonic Solid]

I am not too impressed with PEX. I have yet to work with it but as of now, I am old school.

Not necessarily a bad thing: PEX Plumbing Failures

 

[mires]

Here is my one issue I need advise on is 15'into the house the main pipe tees off to the bathroom thru the floor then runs thru the wall to the sink, toilet, shower in that order. Would you run 1/2 from the trunk line under the house and branch thru the wall? I will try to draw in the computer later this evening.

Run 3/4'' off of the main line TO that bathroom. Then branch off to each fixture with 1/2''. I'm a plumber and as a rule of thumb I always get 3/4" to the room and then branch from there. I try to keep my 1/2'' runs short but there is no reason to run 3/4'' all the way to the fixture either.

 

[sberry]

I wish we had run 3/4" all the way to the laundry tub instead of reducing it !

Why? How fast you want to fill it and eliminating the supply tubes would be the bottle neck. But do you want 2 3/4 valves wide open on a system? It could deliver 30 gallons a minute maybe more. Its already being supplied with 2 1/2 in parrallel if you are using hot.

I agree bigger pipe will not hurt but there is an optimum limit when enough is enough and in some cases less is better.

 

[86k10]

Run 3/4'' off of the main line TO that bathroom. Then branch off to each fixture with 1/2''. I'm a plumber and as a rule of thumb I always get 3/4" to the room and then branch from there. I try to keep my 1/2'' runs short but there is no reason to run 3/4'' all the way to the fixture either.

Is this what you are recommending in this pic? Or are you recommending 3/4 just to the first tee at the sink and 1/2 the rest of the way?