What size PEX for supply lines?

[ShadowAviator]

I am building a small house. (shedhome) The individual fixtures are not very far (15ft-20ft). The water heater, softener, manifold are all right by where the main supply line comes up into the building.

I believe the main supply line is 1" HDPE (I need to double check). I want the main line to adapt to PEX, then through a softener before teeing off, one to water heater and one to the water manifold. The hot from water heater will also go to manifold. From the manifold, I was gonna run 1/2" PEX to all fixtures.

My question is, can I adapt down to 3/4" PEX for the main lines, or should I try to keep in 1" for as long as I can?

My worry is maintaining enough flow. Its my understanding that PEX-A would be okay with expansion fittings. But my local stores carry PEX-B (Viega), so I was gonna go with that and crimp fittings.

Also what would be the best way to adapt from the HDPE pipe to PEX? Does one type of fitting work better than the other?

I have been trying read through other threads for answers, but wanted to double check for my situation.

Edit: I forgot to mention, the supply line comes from the well. This is out in the country on a farm. I don’t know if that changes anything.

 

[ShadowAviator]

Okay, apparently I need to learn to read. The supply line coming in is 3/4” not 1”. Although that is the inside diameter of the hdpe. Isn’t the ID of 3/4 PEX smaller?

So I guess my question still stands? I was told 3/4 PEX with crimp fittings may be too small for the supply lines. That is the reason for my question ultimately.

 

[Sponsor]

 

[Terry]

Often a 3/4" manifold with 1/2" to each fixture will work pretty well. We use 1" for two bathrooms. Though if you're coming off of a softener, I realize that in some places they do plumb starting out with 3/4". They don't let us do that here.
The water heater gets 3/4" in and out"

Typical for a bathroom is 3/4" on the cold, broken down to 1/2" for up to two fixtures and 1/2" for the hot.

I have not used HDPE, though I have used poly. Normally male and female threaded fittings for that.

 

[ShadowAviator]

This is just one bathroom, which technically isnt even a full bath with just a walk-in shower.

The whole building is only 27'x30'. The walls are 16' high which gives me enough head room for a very comfortable 27'x14' loft.

 

[Estrogen Hostage]

For a small house with 3/4” feed than I would use 3/4” trunk lines and switch to 1/2” at each individual appliance. Alternately, your house would be well suited to a manifold system, with a half inch pipe to each appliance. This has the advantage of having no fittings in the wall. Fittings with PEX are a very large restriction so this effect is significant. You might consider small pipes to the washing machine. No bigger than 1/2”, that way it doesn’t fill too fast.

 

[Jadnashua]

I don't feel a WM would ever fill too fast! Mine takes long enough, and slowing down the fill just seems counterproductive. It's not a bad idea to install hammer arrestors on the inlets to it, though.

I'd prefer pex-A with expansion fittings, but if all you can readily find is -B, crimp works, too, but with more restrictions.

Don't run the pex like copper with nice straight runs and fittings to change directions. Do support it per the instructions, though. If you get a tighter turn approaching the minimum allowed, use a bend adapter that fits outside the pipe and makes a nice right-angle bend. Extra fittings create more restrictions that will decrease volume and pressure when water is flowing. I prefer to terminate the pex to a copper stubout adapter as I find just installing a shutoff valve on the pex is a bit too floppy for my tastes. The stubout adapter means it will also stay square to the wall and be firm, assuming you install it that way!

I'd probably use a manifold and home runs. Feed the manifold with the 3/4" (1" would have been better, but not necessarily useful without a larger supply behind it). Except for unrestricted devices, 1/2" pex is sufficient. Tubs, washing machines, and outside hose bibs can benefit from the largest supply line available.

fwiw, 3/4" pex's ID is about the same as 1/2" copper, so 1" pex from your supply would limit the pressure drop to the manifold as it would not be a restriction. In a small space, you may be less likely to be drawing a lot of water at once, so you may not notice the restriction. If, say, you were running a sprinkler outside, you might notice the difference between the 3/4" line and a 1" one, though.

 

[Bruce Garrison]

My experience says that PEX-B with compression fittings is not an adequate substitute. They are horrible. The flow is atrocious. Look at page 6 of this and you will see that there is a 40% (!) reduction in flow.

 

[Bruce Garrison]

And FWIW, if you have to use PEX-B, the metal fittings are slightly larger than the plastic ones. IMHO in the day, no one is restricted any longer to using what is on the shelf.

 

[Jeff H Young]

3/4 even with PEX /crimp I wouldn't think is a problem

 

[Jadnashua]

IT depends on how many outlets are on at the same time.

 

[Jeff H Young]

doesn't hurt to size out your water per code