plumbing layout
hi all, any feedback on this plumbing layout? My house is compact enough that I’m now thinking a manifold system makes more sense than a recirc loop. On city water & planning to use PEX (would prefer type A, but need to buy expander tool). Some questions I have:
– is it worth considering 3/8″ hot water line to the kitchen sink? Would be great to cut wait time there, but not sure it’d be enough flow. And if I did 3/8, would running a separate line for dishwasher be advisable?
– any benefit to running 3/4″ line to an outdoor spigot?
– I could reduce pipe by using a trunk & branch system on the cold side. But where I see people using manifolds, they use for cold as well. Besides giving you ability to turn off individual circuits, does this help keep pressure/temp at fixture 1 more consistent when fixture 2 is turned on elsewhere in the house? Or other reasons?
– My thinking behind running a main line to each bathroom and teeing off from there is to reduce wait times once one fixture “charges” the hot line & to avoid running excess pipe unnecessarily. Also bathrooms are small and designed for 1 person, so not expecting faucet and shower to be running simultaneously. But any problems you see with that?
Thank you!
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A lot of this has to do with what your priorities are in each case. A main/branch system will often be simpler than a manifold system to install, but if your primary concern is hot water wait times, a manifold system with smaller "home runs" to each fixture is probably better. You need to determine what's most important to you first. I'll go through your individual questions though:
1- A 3/8" line would be OK *IF* the run isn't super long. If you can put your manifold pretty close to the kitchen, you'd probably be OK here. I would run a seperate line to the dishwasher, since the dishwasher is likely to be running at the same time as the sink in many cases (handwashing, etc.).
2- A 3/4" line would help if the run is long, or if you expect to have a lot of flow (like an automatic sprinkler system). 1/2" is more typical here, and would be fine for normal "using the hose to water stuff" kind of use. In most cases, I don't think a 3/4" line would be of much benefit, and in the case of a sprinkler system, my preference would be to run a seperate run for that anyway.
3- You don't have to use a manifold for both hot AND cold, you can use a manifold for only hot if you want, and a main/branch system for cold. I think it's more common to do both the same way though. A properly sized main/branch system should be unaffected by multiple fixtures running at the same time in terms of pressure changes as compared to how things would behave on a manifold system. This is because the main run is typically a size or two larger than the branches (maybe 3/8" branches with a 3/4" main, for example), so the main always has "extra capacity" to run multiple fixtures. Either way, the main thing affecting pressure with multiple fixtures running should be the water supply to the system (well, city, etc.). Note that a main/branch system is going to use a lot more different kinds of fittings than a manifold system, which might mean it costs more in the end since you can't get quanity breaks by using a lot of one kind of fitting. The PEX itself is pretty cheap.
4- If this is a compact system, your wait times are probably going to be pretty small regardless. If this is a "compact house" as you state, my preference would probably be for a manifold system, located centrally with respect to the fixture locations throughout the house. This is usually the best way to cut down on wait times overall. With a layout like this, it makes sense to us a manifold for both the hot AND cold runs too, since main/branch systems usually make the most sense when the supply is at the end of a fairly linear overall run (think a long and skinny floor plan with a mechanical room at one end). Compact systems tend to be more clustered, which are good fits for a centrally located manifold system.
Bill
Thanks for the thorough response! And sorry, I just realized that the picture I drew did not actually post. Let me try again.
Those runs are all pretty short. I'd probably just go with a manifold setup for both hot and cold, assuming you can locate it somewhat centrally in relation to the fixture locations. You're probably fine with 1/2" to the outdoor spigots too, and that's what's commonly used for those. I haven't run any 3/8" home runs myself, but I don't think they'd be a problem for something small like handwashing faucet unless the run was quite long. I'd be reluctant to use 3/8" for anything higher flow than that though, especially things like a shower that you want to have reasonable pressure.
Bill
Sounds good, thanks. I'll plan to stick to the manifold set up for hot & cold then, and follow your sizing advice. And yes, the dimensions on the drawing show approx. distance from the manifold to the fixtures. The manifold would be mounted right beside the water heater.
- So (as shown in the drawing) does running a single 1/2" line from the manifold to each bath and then branching off from there seem fine to you? Or are you suggesting a bigger manifold that would allow every individual bath fixture to have its own home run?
- For the ~20' run to the kitchen faucet, would you use 1/2 or 3/8? (water heater will be right next to the kitchen. Line will go up from heater, about 10' through ceiling and then down to kitchen sink). If I do 3/8, will run a separate dishwasher line as you previously suggested.
thanks again!
I'd be fine with a 1/2" run to each bathroom that branches off to multiple fixtures in the bathroom it serves. A bigger manifold just gives you the ability to shut fixtures off individually, which is of limited benefit. Just shutting off one entire bathroom is usually fine, and still much better than the old school way of shutting off the entire house to do any work anywhere.
I would absolutely use the 1/2" line to the kitchen sink. Any low flow stuff on a kitchen sink is a bad idea. You save NO WATER by making it take longer to fill a pot with water, for example. Low flow fixtures in kitchens just waste lots of time and accomplish little else.
Bill
sounds good, thank you!
In your case a simple home run does work as your distances are short.
My preferred method is a semi home run setup. This puts high use fixtures (ie bath/shower, washing machine, outdoor faucet) on their own home run lines. The rest of the fixture can be a single 1/2" trunk and branch setup. This uses much less pipe and it also keeps the volume of hot water down.