Re-plumb house using Viega manablock; questions.

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piperca

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I am going to tackle a re-plumb of my home using copper as the main line from the garage to the plumbing chase that is located in the center of my home. From there, I intend on using PEX-A from a Viega Manablock to supply two bathrooms and a kitchen. The kitchen is on one side of the plumbing chase and the two bathrooms on the other. Everything is very accessible.

I have done quite a bit of diy plumbing over the years and have a construction background (finish carpenter), but have never worked with PEX, so I have a couple of questions and am open to any constructive criticism offered.

I intend on running 1/2” lines from the manablock to all fixtures; is this correct or should I consider dropping some of the lines (bathroom faucet, toilet) down to 3/8”? I’m not sure if there is any significant drop in pressure, while using multiple lines from the manablock, especially if I use all 1/2”; is this a concern?

Also, I was considering using one of the hot ports from the manablock to recirculate hot water from the water heater to the manablock, as I’m moving the water heater outside to the garage (currently inside a closet next to the plumbing chase), which adds approximately 50’ of hot water line to the system. I intend on adding a recirculating pump on a timer to accomplish this. Is there any issues with using the open port?

Lastly (for now), opinions on crimping or expansion collars? I was leaning towards expansion collars, but am open to constructive advice.

Any information/advice anyone can provide would be greatly appreciated.

Thanks in advance,
Andrew.
 

John Gayewski

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Expansion. Use 1/2" not 3/8"pipe. Recirculating lines are generally 3/4" nowadays. The pumps people use are generally oversized and 1/2" recirc is too fast for the pipe.
 

Jeff H Young

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havent worked much with PEX but havent seen 3/8 used around here Ive got to inspect some new homes going up all around me Im sure they all have PEX . and Im betting they are all expansion pex A I dont look at many new homes but reall want to see what these guys are running lately.
Most guys prefer copper stub outs but My house was plumbed 20 years ago with plastic all the way to the anglestop.
I like the theory of Manabloc minimal joints is hard to argue with. Expansion and 1/2 inch sounds like a winner BTW you dont have to run your recirc from the manifold you can go all the way to the end of your farthest hot water fixture and get instant hot water at that fixture
 

piperca

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Thanks for the responses!

I did a little more research and found my idea will not work, as the manabloc is specific to PEX-B only. I found a closed trunk manifold, made by Sharkbite, that looks like it would work. It’s polysulfone construction and has 3/4” service with 6 x 1/2” ports. I understood, with the closed trunk manifold, service would suffer, if too many ports from the same manifold are in use; is this correct? Having a manifold in a loop system would be much better, correct? They do offer them in an open trunk configuration, but with fewer ports, which would work fine; thoughts?
 

John Gayewski

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Thanks for the responses!

I did a little more research and found my idea will not work, as the manabloc is specific to PEX-B only. I found a closed trunk manifold, made by Sharkbite, that looks like it would work. It’s polysulfone construction and has 3/4” service with 6 x 1/2” ports. I understood, with the closed trunk manifold, service would suffer, if too many ports from the same manifold are in use; is this correct? Having a manifold in a loop system would be much better, correct? They do offer them in an open trunk configuration, but with fewer ports, which would work fine; thoughts?
I personally don't see an advantage to using a manifold system on a house. I don't see the advantage of running so much extra pipe but that's just me. One well insulated truck circulating hot water close to the fixtures is my preferred method.

You could have a dedicated return manifold, where every fixture you wish to circulate returns, it would need balancing valves.
 

Jeff H Young

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I just like not having any joints of course there are going to be some on other hand all the spaghetti isn't that desirable either.
 

piperca

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After reading the responses, I’m leaning towards running the 3/4” line (looped), with a small manifold stubbing out at each location (each bath and kitchen) to accommodate each fixture. More main supply line, but less 1/2” runs (couple/three feet) to each fixture. I’ll have more joints with the fittings to create the loop, but I think it’ll be a better system. I’ll add one 3/4” return at the end to recirculate the hot side. I’ll be insulating both sides, since my cold will be exposed to the attic heat. California summers get HOT!
 

JoeJee

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If you are using PEX-A look at "Uponor Logic Plumbing" (there are other names for this regardless of the type of PEX). Basically it is they hybrid of Trunk/Branch and Home Run.
 

Jeff H Young

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I often insulate hot and cold as well with copper it makes for a quieter system an added benefit .
 
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