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The very popular general plumbing, toilets, sinks, faucets, pump problems, questions and answers discussion Forum
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Author:
Curley (PA)
Hi. I'm running single lengths of pex from 3/4 in trunks in the basement to each fixture in the house. Sort of a modified "home run" system. My question: can I run 3/8 in. HW lines and 1/2 in. CW lines to the bathroom lavatories? I was thinking that the 3/8 in. line would save on hot water and reduce HW wait time. Is is ok to run different size lines like this? Thanks in advance for your helpful replies.
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Author:
hj
If you think 3/8" hot lines will give you all the water volume you need, then why bother using 1/2" for the cold, because it will use the same amount of water. 3/8" lines WILL have less water in them, but they also have MUCH MORE surface area compared to the volume of water in them so they can lose more heat until everything gets heated up from the flow of the hot water.
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Author:
jimmy-o (CA)
The "ivory tower" plumbing code types are investigating and ruminating on just this issue. Your thinking is what they are thinking...that a 2 gpm shower or a 1.5 gmp lav may be adequatelyt served by a smaller line, and water can be saved because there is less volume that has to be flushed out before it gets hot.
It is not a simple question, andt there is no one right answer at this time.
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Author:
SwimRunPlumb (MI)
I think he is correct in his assumptions. The times that you will use the hot shortly after you have used it (while it is still hot), will be very few. This means you shouldn't be concerned with how fast it will lose it's heat, as hj was pointing out. I think you just assume the line is going to lose all of it's heat everytime you want to use it again, and therefor a quicker delivery time would be ideal.
As hj also stated, there is no reason to run 1/2" to the cold.
I would only do this for the lavs and sink(s), I would not run 3/8 to any tub or shower.
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Author:
Curley (PA)
Thanks for your replies. Yes, I was planning on using the 3/8 line for only the bathroom sinks, not the tub or kitchen sink. Why not use 3/8 for the cold water lines? Well...I bought all of the parts to use 1/2 in. for everything except the 3/4 in. trunk lines. And then I realized that this could waste alot of hot water. So I thought I'd check with the forum on this issue so I wouldn't have to get all new tubing and fittings. Fortunately, I haven't removed or installed any parts yet. I was concerned that using different sized lines could be a code violation, but it looks like it's not.
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Author:
hj
I was pointing out TWO things;
1. How fast the water will lose its heat when the flow stops, and,
2. How long it will take before the water KEEPS its heat when flow starts.
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