plumbing question

[Michael Weber]

I know there are several plumbing forums available but this is simple so I figured the users here could help. I'm getting ready to upgrade water lines in my house to PEX using a home run system. Every device will have a separate hot and cold line running back to a manifold. I'm thinking that for everything except tubs and showers a 3/8 diameter line will suffice. Tubs and showers would get 1/2. Sinks, commodes, dishwasher, clothes washer would be okay with 3/8 inch. I have some runs that will be quite long (2 story house) and want the smaller diameter to provide hot water more quickly. Does that sound right? Thanks, Mike

[John Lanciani]

If it were me I'd stay with all 1/2" just to make the installation quicker and simpler. I don't think the small savings in water or the few extra seconds waiting are worth the added complexity of having two sizes of everything (for the install and for long-term maintenance). If you haven't already, check out supplyhouse.com (formerly pexsupply.com) for your job. Much less expensive than the borgs...

[Mark Bolton]

We run all 1/2" and no 3/8". I cant say for sure but I dont think you would be satisfied with 3/8" if your runs are of any length. A house I just finished has some runs that are perhaps 60-70' from the manifold. Manifold is less than 5' of 1" copper from a Navien on demand water heater. If I recall correctly it was about 20 seconds for hot water to those longest runs. We didnt opt for re-circ because the customer is using that bath primarily as a guest bath so that amount of time for showers isnt too unreasonable.

I have personally never used 3/8" on a job so I cant say for sure but I will say there is a noticeable pressure drop on long runs with 1/2" and it would be substantially worse with 3/8". The reduction at the fitting will be the real crusher.

[Jay Jolliffe]

I plumbed my house the way your describing with manifolds & lines to all fixtures. I used 1/2 pex for everything except the water conditioner & furnace where 3/4 & 1'' copper was used. We also use an on demand water heater.

[Jim Matthews]

Be advised that PEX likes sweeping curves and straight runs.

Trying to get 90 degree corners without kinking the line can be difficult,
and adds expense. Have you run this stuff before?

There are some warnings out there about line formulations that are prone to
pinholes, and the aluminum jacketed versions are unwieldy for first time users.

[Brian Elfert]

The aluminum jacketed PEX is not normally used for potable water.

[Mark Bolton]

Be advised that PEX likes sweeping curves and straight runs.

Trying to get 90 degree corners without kinking the line can be difficult,
and adds expense. Have you run this stuff before?

There are some warnings out there about line formulations that are prone to
pinholes, and the aluminum jacketed versions are unwieldy for first time users.

Could you post the current information about pinholes? I was on the supply side of the pinhole issue WAY WAY back in the late 90's and into early 2000's but I havent read a single current account of pin holes in any of the newer products.

Not questioning your information but it wouldnt be fair to the product to toss out info that isnt accurate.

[Chris Padilla]

I just bought some 3/4" PEX (from supplyhouse.com formerly pexsupply.com) to put in a dedicated hot water return line (Grundfos pump) and I'll be using some sharkbite fittings here and there for various turns. I'm remodeling our master bathroom and I'll attach the line to the hot side for the shower. This is the longest hot water line in my house and I'll have access to it. I haven't heard anything about pinhole problems. I'm running the line through my attic so I'll be insulating it as well.

[Mark Bolton]

I haven't heard anything about pinhole problems

Of course don't know for sure but my gut feeling is the reference about pinholes has nothing to do with PEX but rather is confused with a MAJOR issue with quest tubing many years ago. This was a major affair at the time but is a 25 year old issue and not even remotely the same animal as PEX. In the area I was in suppliers had touted the product and it swept through large developments and apartment complexes/condos. When the failures hit it was a total disaster.

Hopefully Jim will clarify his claim.

[Erik Loza]

I know little about plumbing except to tell you that when we house remodeled a couple of years back (100% new plumbing all the way to the water meter...), the contractor used 1/2" PEX on everything. Zero issues with water pressure upstairs, even while running both shower heads simultaneously. We do have decent water pressure (50psi+) from the street, for what that's worth. My thinking was that from an install perspective, it's easier and simpler to keep everything one size.

Best of luck with your project.

Erik Loza
Minimax USA

[Tom M King]

In one really old house where we made runs up to the third floor, I put the PEX in plastic electrical conduit. I don't remember the size of the conduit, but it was maybe 1-1/2". We glued all the joints and the PEX went right in with the sweep elbows. An electrical "fish tape" was used to pull the 1/2" PEX. We glued all the joints in the conduit. The thinking was that we wanted no chance of any future water damage to the expensive, old work, and the pipe would be easily replaced 75 years in the future. If there would ever be a leak in the line, the water would run back out the bottom of the conduit under the house. I'd consider doing this in new construction in some situations.

Plastic conduit is cheap. We also up the refrigerant line, and condensate drain in plastic conduit from the third floor air handler.

[Chris Padilla]

In one really old house where we made runs up to the third floor, I put the PEX in plastic electrical conduit. I don't remember the size of the conduit, but it was maybe 1-1/2". We glued all the joints and the PEX went right in with the sweep elbows. An electrical "fish tape" was used to pull the 1/2" PEX. We glued all the joints in the conduit. The thinking was that we wanted no chance of any future water damage to the expensive, old work, and the pipe would be easily replaced 75 years in the future. If there would ever be a leak in the line, the water would run back out the bottom of the conduit under the house. I'd consider doing this in new construction in some situations.

Plastic conduit is cheap. We also up the refrigerant line, and condensate drain in plastic conduit from the third floor air handler.

I like the over-engineering there, Tom!! Bravo!!

[Malcolm Schweizer]

I recently bought a house and everything is run with 3/4" pipes. I added an on-demand hot water heater, and it takes a long time to clear the lines before the hot, so I would say go 1/2", which is what other homes I've lived in had, and there were no pressure or flow issues.

[Michael Weber]

I recently bought a house and everything is run with 3/4" pipes. I added an on-demand hot water heater, and it takes a long time to clear the lines before the hot, so I would say go 1/2", which is what other homes I've lived in had, and there were no pressure or flow issues.

Yes, you should. Someone thought they were doing themselves a favor by going 3/4 probably to avoid what they thought was a pressure drop issue. That's basically why I was asking about 3/8 instead of 1/2 for non critical things like bathroom sinks.

[Jay Jolliffe]

The gas on demand water heater I put in said to use 3/4" pipe....