PEX manifold with long runs — oh my
I am currently designing a home in Zone 5, an hour outside of Philadelphia. My foundation will be a slab-on-grade; Stem Walls & 4″ slab, fully encapsulated in EPS insulation. The home is a single story, 1248 square feet. I have two questions regarding plumbing…
1. is there an advantage to running the PEX tubing within the slab or not? I do have adequate room within the ceiling to run all water supply runs, so I could do either, just not sure of the pros vs. cons.
2. I had originally planned on home-runs to each toilet, sink, shower, dishwasher, etc., and back to central manifold. My builder recently approached me and recommended running a larger trunk to each bathroom/kitchen and branch off the trunk for individual water lines. Comments?
I have attached a copy of the floor plan… the longest run will be about 40′ from utility room to master vanity.
any suggestions, recommendations, comments, are welcome.
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Replies
My preferred method for hot water is main trunk and branch. This makes hotwater recirc much simpler. A single recirc line at the end of the trunk now serves the whole house.
Cold water can go on a manifold. Cold water feeds should go where simplest (celing is easy). It is always best to insulate the main feed to the water tank as it will prevent condensation when there are big water draws.
My favorite mechanical contractor at work would tell you that manifolds are awesome, and that they let plumbers work like electricians turning off only what they’re working on and not the entire house.
I would say “it depends”. Hot water on a main line makes a recirculating system possible, but will also make it take longer for water to get hot at the farthest fixture since you will likely have a larger diameter trunk line. Trunk lines tend to make sense when the hot water heater will be installed at one side of the house and won’t be centrally located. Trunk lines also work well when all the fixtures are in an approximate straight line. A trunk line will probably require less total pipe insulation, and might be less work to install depending on the particular layout. If all your fixtures are approximately equidistant from the water heater, or if they’re all randomly distributed around the floor plan, then a manifold probably makes the most sense.
Cold water is similar, but with no consideration for a recirculating system. You could potentially use a manifold for some fixtures and maybe a “trunk” line for the most distant two fixtures (like a toilet and sink, for example), to reduce the total amount of pipe. The trunk line might be less total labor to install due to fewer hangers and holes being needed.
I would absolutely NOT run any lines in the slab unless you’re putting in radiant heating pipe. I would also not put any plumbing in any exterior walls.
In your particular layout, I’d use a manifold for everything (both hot and cold) except for the master bath. I’d tee the shower and sink in the master bath off of a single pipe run for each of the hot and cold lines. If you keep the tap length for the shower short, you can always add a recirculating system on that one long run later, but you get the convenience of the manifold for everything else. The relatively short pipe runs combined with the smaller diameter required for the single fixture pipe runs will keep hot water wait time to a minimum for everything served by the manifold.
One last thing: make sure to use the metal compression ring connectors and not the plastic snap rings. I’m not sure I trust shark bite fittings over the long term either. I don’t like using fittings that require a gasket in any concealed locations.
Some friendly advice from an EE: use a 40 space breaker panel instead of a 30 space. There is little, if any, cost difference, and they’re similar in physical size. You never want to use tandem breakers unless you have to, and you can use GFCI breakers instead of receptacles for better long-term reliability. Thank me later :-)
Bill
Ron,
Forgive me as this is unrelated to the question you asked, but why do you have a complete 2"x10" framed structure under your trusses?
the final plan is a complete 2"X10" framed floor under a framed roof. this is an older copy of the plans with old notes. this tells me you reviewed the details of the plans... and for that I thank you!
Ron,
Also I think your fridge is too close to the wall. With most french door fridges, you need to open the door more than 90deg to be able to remove the crisper drawers.
good catch! this is something that has been corrected. our solution is to either widen the opening from the mud room to the kitchen or shifting the opening, pushing the opening just slightly past the refrigerator door hinges, allowing the door to swing past 90 degrees. I appreciated your input and taking the time to review the details of the plan.
Manifold system will use 3 times as much pipe. Use more labor and waste more water.
You may find these articles interesting.
I see no problem putting pipes under the slab knowing they will need to be replaced in 30 to 50 years.
http://garykleinassociates.com/PDFs/15%20-%20Efficient%20Hot-Water%20Piping-JLC.pdf
https://www1.eere.energy.gov/solar/pdfs/sda_saving_water.pdf
Walta
That is probably true for some houses, it may even be true for a typical house. For this house, the difference in length of pipe is going to be much smaller between the home run and trunk/branch system. The two longest runs are to the kitchen sink and the master bath. There is nothing between the water tanks and the kitchen, so there's no pipe savings possible there. The laundry could tee off a branch and carry on to the master, saving about 25' and the water closet could tee off the same branch, saving about 12'. You could have the master sink and bath share lines, which would be the biggest savings, maybe 80'. I would opt for a hybrid system. Home runs to the kitchen, laundry (tee the laundry sink off the washer lines) and water closet because they are pretty short anyway, and run a trunk down to the master bathroom and branch to the tub, sink and toilet. It's not clear on the drawing where the outdoor spigot(s) will be.
Why are you asking your builder instead of your plumber?
domestic water lines in the slab ? What happens when they need maintenance? Are you going to break up the floor? Nothing wrong with putting them elsewhere..
Ron,
Except for radiant heating no water lines get run in the slab, they get run under it. It isn't a first choice, but rather something you sometimes have to do out of necessity. For pex under a slab I run it in 3" pvc conduit with sweeps. That way it can be replaced if necessary.
Hi Ron,
I like plumbery so I thought I'd chime in.
1. Don't bother with plumbing in the slab since you can run it in the attic. Good practice in slab would be to create abs conduits with no lips to be able to feed/pull the PEX. Also you can't or would be hard pressed to insulate the hot lines. It's a lot of unnecessary work.
2. Based on your floor plan, you don't have many fixtures and they're all very close to the utility room. I'd say it would be easier to splurge on the central manifold and run individual lines in the attic. In my best guess without doing any calcs, and based on big Gary's material, Your wait times for hot water would be minimal in a home run system vs a trunk system without a recirc.
In my current build I have 3 floors + basement. I originally thought I'd do a viega home run system, but based on the amount of vertical travel each line would be, I switched to main and manifold system to save on material and labour. I ran a 1" PEX main to all floors serving a manifold on each floor. The manifolds have 1/2" branch lines with ball valves so I can control each line and the ends of the hot manifolds have a home run for a recirc system.
If there is some fixture where the wait for hot water bothers you, consider adding a dedicated (water heater to fixture) 3/8" or 1/2" (use a online calculator) line for it. Perhaps 10 seconds vs 1 minute (longer than you might calculate since 3/4" typically won't achieve "plug flow").
A centrally located water heater can halve the longest wait times.
Use a low flow shower head (I use 1 GPM which is fine in 3/8" PEX).
You don't need to do a full home run system or a full trunk and branch. You can always do a hybrid where you have some fixtures that share a 1/2" line. This gives you the advantage of getting hot water there quickly as 1/2" uses half the water that a 3/4" line would, so no need to flush the entire trunk before getting hot water. This also saves you from needing recirc pumps.
The whole idea of using larger diameter pipes to feed fixtures is so each fixture has the proper flow if multiple fixtures are being used, eg a 3/4 x 1/2 x 1/2 tee will deliver an equal and proper amount of water to each fixture, whereas a 1/2 tee feeding two fixtures will have its volume cut in half.
A manifold may not quite add up depending on the size of the manifold, eg. a one inch manifold supplying x number of fixtures will show a larger drop in volume flow rate as opposed to an 1 -1/2 manifold serving the same number.
That only applies when all fixtures are running full out, a scenario that doesn’t happen very often. You can apply demand factors to reduce the size of large trunks.
Also, most fixtures won’t even flow the full amount of water a 1/2” pipe is capable of delivering, so there is often no need to oversize a supply line.
Bill
Bill, best to check your plumbing codes. Depending on the fixture type, it will demand a certain amount of volume flow. The piping should be sized accordingly or else fail your inspection.
Be careful when they spec PEX as the inside diameter of the fitting vary from one type/ brand of PEX to the next. Some brands the 1/2 inch flows about the same as 3/8 copper and 3/4= 1/2
Walta
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Walter,
This is one of the main differences between standard PEX (pex-b) and wirsbro/upanor PEX (pex-a). Or any system that works with the F1960 standard where the fittings are the same internal diametre as the pipe.
Even F1960 fittings are smaller id then the pipe. For instance a ProPEX 3/4 fitting has a minimum ID of .590, while the 3/4 pipe has an ID of .671
Jamie
I agree with you that PEX A and B are different the problem is when you get bids or talk to the plumbers some will gloss over the differences and just say PEX. Like I said let the buyer beware.
Walta
I'm not sure the standard pex crimp fittings that reduce the size of the opening make any appreciable difference to a house's plumbing. The fixtures themselves (diverters, taps, valves) typically restrict flow in a similar way. Which parts of the water supply are noticeably affected by the standard pex plumbing rough-in?
Well if you believe that a fixture can restrict flow, then why are you not sure if a fitting, or reduced opening can restrict a flow, which of course they most certainly do. Friction causes pressure drop, which leads to a drop in velocity and thus volume of flow per time. Plumbing codes are based on scientific principles and charts are devised to properly size water and waste piping. So instead of guessing, consult your local code books.
All PEX, whether type A, B or other is manufactured to the same ASTM dimensional specification. The difference is in the fittings, as type A is suitable for cold expansion and therefore can stretch over larger fittings. I think it's debatable whether this makes a significant difference in flow rate. I used Uponor type A, but mostly because I've seen leaks with type B crimp connections before. The lower restriction fittings I saw as just a bonus.
½ inch PEX is a useless for anything but a single toilet or a single modern low flow faucet, all other applications need ¾ inch PEX.
I let my plumber use “PEX” I failed to ask any questions. He plumbed the hose bibs with ½ PEX the flow after 60 feet of ½ inch PEX with 10 elbows is so low sprinklers will not move. The fix was to up size the PEX to ¾ finding a way to connect the hose bib without using a ½ inch PEX fitting was a challenge but do able. The flow rate for 5 gallons went from 3 minutes to just over a minute.
The showers are fitted with ½ PEX the flow is not strong it is almost acceptable if you use a 50/50 mix of hot and cold! I am seriously considering ripping out the drywall and replacing the pipes.
In the photo you will see the largest drill that will fit in a ½ PEX fitting 11/32. That is 2 drill sizes below 3/8. A 3/8 bit would fit inside 3/8 pipes and fitting.
In the next photo you see the 11/32 drill inside a ½ copper pipe. This photo shows clearly why ½ inch copper will flow 3 times as much water as ½ PEX.
Walta
Walta, is that 1/2” PEX you’re referring to 1/2” ID or 1/2” OD? I’m surprised you’d be seeing such a flow restriction from only 60’, although many types of PEX fittings are much more restrictive to flow than the copper pipe fittings are since the PEX fittings protrude inside the pipe.
Bill
> ½ inch copper will flow 3 times as much water as ½ PEX
If you calculate everything (copper fittings and pipe are larger, PEX is smoother, PEX has fewer fittings, FPM limits, etc) it's more like 20% more more flow (for a given pressure drop) than 300%. Very short sections of smaller diameter (such as PEX fittings) have little effect.
Maybe Canadian 1/2 pex is larger (metric system and all). No issues feeding a shower with two rain heads with 1/2 pex.
The things to avoid is fitting with sharp bends. Standard 90 deg bends and T branches add a lot of loss. The smooth 90 deg fittings are your friend.
Every 90 elbow on 1/2" PEX adds 8-10 feet equivalent length, depending on fitting type. Ten elbows and probably a couple of other fittings plus 60' is too long a run for 1/2" PEX and a 5GPM demand; that's a 40-50psi pressure drop. The major advantage of PEX is that you can bend it, and avoid the use of elbows in most cases. Your plumber didn't do his job. I plumbed my whole house with PEX and didn't use a single elbow.
Millions of homes have 1/2" PEX and don't have the issues you have, which says the problem is with the installation rather than the PEX in general. I can understand your frustration, but you've taken your experience and misattributed the root cause. Modest length runs of 1/2" can quite easily supply adequate pressure and flow for a standard shower and even a bathtub.