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Discussion Starter · #1 ·
I've decided to use a Pex manifold on my house. I'm also going to be using a gas instant water heater.

My question is, is there a recommended maximum distance from the water heater to the faucets? I think the longest distance is about 50 feet. From what I've read, since these are home-runs I will be using 1/4" line which should make the hot water get to the faucet fairly quickly.

Does all of this sound ok to the experts here?

Thanks!

GT
 

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I'm no plumber, but 1/4" line sounds too small to me. You'll have great pressure, but no volume, and I believe higher volume will get the hot water there quicker.
 

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Discussion Starter · #3 ·
I'm no plumber, but 1/4" line sounds too small to me. You'll have great pressure, but no volume, and I believe higher volume will get the hot water there quicker.
You are right... I misspoke. I thought I had read 1/4" when I was looking at manifolds but now looking at it it seems that they are 1/2". Sorry about that.

GT
 

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1/2" sounds a little more normal. I wonder if doing 3/4" manifolds then dropping to 1/2" nearer to the faucets might not work too. That way you would have better volume delivery and the drop in size would ramp up the pressure near the faucet.
 

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Discussion Starter · #5 ·
1/2" sounds a little more normal. I wonder if doing 3/4" manifolds then dropping to 1/2" nearer to the faucets might not work too. That way you would have better volume delivery and the drop in size would ramp up the pressure near the faucet.
I think 3/4" is way too high. Most homes are supplied with 3/4" I think. Plus, since this is home run (one line per faucet) it doesn't need the flow like other systems.

The manifolds all seem to be supplied with 3/4".

GT
 

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Sean
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The shorter the distance the better - 50' is doable but that is a lot of cold water to flush out - not sure of codes in your area but past 20' (on 1/2") requires pipe insulation per the 2012 http://blog.sls-construction.com/2013/insulating-water-lines-worth-it

TheGrizz - the best thing about PEX is the lack of fittings and smoother corners cutting down on issues with flow - in some cases going smaller than codes would be better but not allowed as they base things off of copper with fittings for their charts
 

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On hot water lines, I would run 3/4 to the farthes point in the line. Use Tee's to pull off hot water to fixtures. Then at the end of the line I would run the 3/4 back to the water heater and add a recirculating pump and timer. Instant hot water to all fixtures.

Read user comments on Watts hot water recirc at Home Depot web site.
 

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I would never recommend a manifold pex system....its very wasteful

probably 3-4x the materials and if you run the water to a sink it does nothing to get hot water to the shower....your wasting all that water to run the hot to the shower every morning and letting that hot water sit in the sink pipe when it could have been used in the shower

I see no reason to do a manifold pex system...it just doesn't make sense...sure it looks nice

waste of time and money installing it
waste of time and money every day its in use

ive seen a few manifold pex system in parade of homes models, but in real life ive never seen one...people look to save money and time
 

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Trees are Cool
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What about 3/8" tube. It is half the volume of 1/2". So the hot water will come to the sink in half the time. That is what I am going to do in the bathroom at the far end of the house from the water heater. I am not sure of the fluid dynamics, but 1/4" seems to small. If you step down, from the manifold at 1/2, to the main line which is 3/8 to the faucet where it goes down to 1/4". My understanding is that you don't want to go up in diameter, or you lose volume.
 

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You gain volume, and flow rate with bigger pipe.
 

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You gain volume with steps up in pipe diameter but you lose pressure, the reverse is true with steps down. You lose volume but gain pressure. This is why most houses, at least the ones I have worked on, are supplied with 3/4", then at some point, the 3/4" steps down to 1/2". I've never seen in wall plumbing smaller than 1/2".
 

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I would never recommend a manifold pex system....its very wasteful

probably 3-4x the materials and if you run the water to a sink it does nothing to get hot water to the shower....your wasting all that water to run the hot to the shower every morning and letting that hot water sit in the sink pipe when it could have been used in the shower

I see no reason to do a manifold pex system...it just doesn't make sense...sure it looks nice

waste of time and money installing it
waste of time and money every day its in use

ive seen a few manifold pex system in parade of homes models, but in real life ive never seen one...people look to save money and time
The only plus I see to them is a convenient way to shut off each fixture. And they look cool.
 

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It depends upon how the building lays out and where you are locating your water heater in relation to those loads. This is very important with any water heater, but especially tankless. Btw, Never call them instant. There is a story there that cost me a lot of dough, due to using inaccurate terminology. I don't have a problem with a manifold if everything is really close. I just built a new kitchen, two baths and laundry room here at the house. The longest hot line is 16' from the water heater and I manifolded almost the whole thing except the tub and master shower. Everything steps right along. The thing to be careful of with pex is the supply pressure. My old well pump set-up is 40-60#. Everything is fine at 50-60#. Not so good at 40-50#, which is driving me more nuts than she who must be obeyed. I had planned on a Constant Pressure well pump but will now definitely do so…soon.

You say you may use 1/4" or 3/8" pex. Personally, I can't imagine doing so. Check the "bushing" sizing of the fittings. I think 1/2" is 3/8, 3/4=9/16 and 1=13/16. That can create a problems for you flow wise.
 

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Discussion Starter · #16 ·
It depends upon how the building lays out and where you are locating your water heater in relation to those loads. This is very important with any water heater, but especially tankless. Btw, Never call them instant. There is a story there that cost me a lot of dough, due to using inaccurate terminology. I don't have a problem with a manifold if everything is really close. I just built a new kitchen, two baths and laundry room here at the house. The longest hot line is 16' from the water heater and I manifolded almost the whole thing except the tub and master shower. Everything steps right along. The thing to be careful of with pex is the supply pressure. My old well pump set-up is 40-60#. Everything is fine at 50-60#. Not so good at 40-50#, which is driving me more nuts than she who must be obeyed. I had planned on a Constant Pressure well pump but will now definitely do so…soon.

You say you may use 1/4" or 3/8" pex. Personally, I can't imagine doing so. Check the "bushing" sizing of the fittings. I think 1/2" is 3/8, 3/4=9/16 and 1=13/16. That can create a problems for you flow wise.
Thanks for the advice! Nice 2002 by the way. :)

GT
 
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