Copper pipe sizing. Is bigger better?

I am ready and about to buy materials for the repiping from galvanized 1/2" to copper ?", but what size to use? I would like to go with 1/2" type K but that takes up more inside diameter then M and L. Should I go with 5/8" K, 3/4" K or just not be worried about the inside diameter because it is a very small difference? Then again the galvanized pipe probably has only an 1/8" openning anyway from all the years of crap in it.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Im not good with piping but i know the closer to the faucet or fixture the smaller the pipe.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Paul J wrote:

What are you re-piping and what is it fed by? Most piping to faucets is half inch from a 3/4" main trunk. Mains from the street are usually 1".
--
Ed
snipped-for-privacy@snet.net
http://pages.cthome.net/edhome
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
M type is for heating lines, L is for "normal" house plumbing. K is for special applications. K is generally only available at plumbing supply houses and K is much more expensive. Use L...

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I vote for L. One of the benefits of DIYing is that you can use a little higher grade of material than a contractor worried about bid price might propose.
http://www.sizes.com/materls/pipeCopper.htm#DWV (and I don't know who's behind that site) speaks of L as the normal "most purposes" pipe - but of course M is very, very common in household use.
That site also has a nice table by which you can compute inside cross-section areas, which would be the primary determinant of flow rates (area=3.14 x (half-the-diameter)-squared, but you knew that). By may calculations, L has 6% less area than M at the 3/4" size, 8% less at 1/2".
Chip C Toronto

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
paul snipped-for-privacy@bankone.com (Paul J) wrote:

Use type "L" copper, it doesn't kink up when installing as easily as "M". "K" is for real heavy duty uses, not home plumbing.
A 1/2" pipe is good for a single fixture (slightly more), and 3/4" is good for like 3. If your faucet is a long way from the hot water, a smaller supply line will supply hot water faster.
I'm replumbing my 50 year old house with 3/4" and 1/2" type "L" copper and am happy so far.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I believe that the 1/2" copper is a direct replacement for 3/4" iron pipe. 1/2" iron pipe is totally inadequate for any modern house. If it were my house I would replace the larger runs with 1" or 3/4" copper and the branch runs with 3/4" or 1/2" copper. Follow what others said about the type of copper pipe
Paul J wrote:

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Actually, 1/2" and 3/4" copper or galvanized has the same OD although the ID of L and M copper will be only slightly larger than galvanized and roughly about the same a K copper.
But.... with water conservation fixtures, what's the need to go to so much larger tubing until we figure the peak demand that's needed for the system? You do that by adding up the max gpm of each fixture or use the fixture count method. And in new construction and many repipe jobs, homeruns, like running Romex, using PEX is being used with excellent results. No fittings except one on each end of the run and each run is valved at a central manifold.
Gary Quality Water Associates www.qualitywaterassociates.com Bulletin Board www.qualitywaterassociates.com/phpBB2/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Gary Slusser wrote:

It isn't the size it is the smoothness of the pipe wall that makes a difference in flow. Sizing pipe based on the flow needed is driven by economics. As a homeowner, especially a do it yourself homeowner, economics is only one factor and may not be the most important factor for me. I would use a larger size of pipe to reduce flow noise, a larger slower fan and larger ducts to reduce air noise, a larger size wire to reduce voltage drop, heavier floor joists and subflooring for greater solidity, thicker outside walls for comfort and sound control, etc. If I eliminate the labor cost, and since labor is a major cost in any construction, I can devote more capital toward premium construction elements.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Problem is George you were giving him advice, not speaking as to how you'd do it. But I agree with you, you're not a plumber. You also don't know what you're talking about IMO when it comes to sizing water line. And if it weren't so late, I might prove it but it is late. And I doubt you'd get much out of it anyway. I'd really like to hear more about the smoothness and less water noise in larger pipe though, I see a full pipe regardless of the ID or smoothness so there will be no water movement noise. There's only one chance to get the pipe sized correctly, and that's at the beginning when sizing it; regardless of smoothness or whatever, it's the ID of the pipe for the job it has to do, and that's delivering the amount of water the system needs.
Gary Quality Water Associates www.qualitywaterassociates.com Bulletin Board www.qualitywaterassociates.com/phpBB2/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Gary Slusser wrote:

Good grief! No water movement noise? What the hell is that about, how do you get water out of a faucet if the water doesn't move? I suggest that you look at a 2 foot wide stream that is flowing 30 cfm and then a 10 foot wide stream flowing the same amount and listen to which one is making more noise. The same principle applies to flow in pipes.
You seem to think one size of pipe is correct. Not true and you know it. What is true is that a pipe below a certain size won't deliver an acceptable about of water. Anything above that will deliver an acceptable amount of water. It takes about 1.5 hours maximum for the slowest reader to compare several sources as to normal and minimum acceptable sizes of pipe. There is about as much science in sizing pipe for a single family dwelling as picking out the size of the family car.

So I read a book and that says 1/2" copper is a flow substitute for 3/4" iron. Actually several books say that. Picking a size for a water line in a single family dwelling requires about as much information as you can get in about 1/2 hours of reading for a slow reader. Any good book will tell you what sizes are acceptable throughout the house. There is no single size that is correct. There a sizes below a minimum that will not be satisfactory. Hell, if you want the fast way just look at the outlet from the meter and use that size throughout the house; got a 1" supply from the meter,then use 1" throughout the house. While that is obviously overkill If the inlet from the
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote

George we are talking a full potable water pipe, and probably cold water at that, an enclosed water line. And certainly not some open ditch. We also aren't speaking of the water as it exits the faucet or fixture. where the noise is caused by the water splashing or the aerator makes noise.
Yes one size pipe is correct for the specific house it is installed in. Science... or actually math, is applied to find the (acceptable) velocity of the water in whatever pipe size we use. The standard acceptable velocity is not more than 6-7ft/second in whatever size pipe to be used. The velocity is dictated the size of the pipe. The velocity is dictated by the size of the pipe and the PRESSURE applied to whatever size pipe we select but there's only one size correct for that specific water system. Only one size is correct per installation because we have to base the pressure used on open/running fixtures gpm requirement to calculate the velocity.
That part about 3/4" iron/galvanized and 1/2" copper... yes, you'll always get more water through 1/2" copper than a rusted up, full of encrustation filled galvanized pipe, but not a clean one. With a clean one, you get more water by about 2-3 times more with the 3/4". Prove me wrong if you can. And it 'is' more the size of the pipe than the smoothness of the pipe, and plastics are about the smoothest you can find; hard water scale does not stick to the inside of plastics, nor do they rust or corrode which causes roughness.
Gary Quality Water Associates www.qualitywaterassociates.com Bulletin Board www.qualitywaterassociates.com/phpBB2/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Gary Slusser wrote:

I know what we are talking about. We are talking about the noise of water running through pipes. I've lived in houses with noisy water lines. Most noise is caused at valves and then transmitted to the walls through the pipes. And, the largest noise makers are usually the valves associated with the water closets. The second noisest in my experience is the outside faucets. But any constructed point in the water line is a potential noise maker. And no, we aren't talking about the noise of water splashing. We are talking about the kind of noisy you hear when you are 30 or 40 feet from a fixture and separated by several walls.

That's pure BS. There is a MINIUM pipe size based on acceptable flow rate. Even you admit that, by saying you want to maintain a water velocity of 6-7 feet per second, because the way you reduce velocity is by increasing the size of the pipe. There is no MAXIMUM pipe size unless you want to base it on pure practicality or economics. Most fixtures have short, small (1/4" or 3/8") pipes between the fixture and the supply line that determines the flow through the fixture, or the fixture itself may have smaller openings that determines the maximum flow or the supply valve may be the flow limiter. It doesn't make any difference to the flow out of the one fixture if the supply line is 1/2", 3/4" or 1 inch. Unless, you have several fixtures flowing which reduces the pressure and then you want the supply line to be larger.
There is no single size correct for water pipe any more than there is a specific size for a bed room. If you like a big airy room, then make the bedroom big. If you like a lot of flow even when other fixtures are open, then use large diameter pipes. I doesn't make much sense, unless you have a long run, to use pipe larger than your metered supply. And yes, here we have an option of 3/4" 1" and 2" meter supply.

Hey, I don't know if it is true or not but several books on plumbing indicate that 1/2" copper will replace 3/4" iron because of the greater flow rate through copper and they weren't talking about rust filled iron pipes. I do know that iron pipe, especially when you consider the elboes and other connectors can be extremely rough compare to copper.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I've been around a lot of water pipe and haven't experienced the noise you have.

Which goes to your suggestion of 1/2" to replace a 3/4" galvanized water line; the basis of my reply to this thread.

I said the selection of the pipe size is dictatd by the velocity and velocity is dictated by the pressure the system requires.

This is a DIYer you're advising, Why would he want to buy and install a larger pipe than he needs?

True, and you add them all up at maximun flow rate and figure what peak demand flow rate the pipe size has to provide.

Listen to what you've just said: Unless what? And then you need what? More pressure? The problem is you don't have enough flow at the pressure the system is operating at. Which goes back to your statement that his 3/4" galvanized can be replaced with 1/2" copper with 2-3 times less WATER delivered. If he does that, his velocity will be too high and that causes water hammer damage to the entire system. Then he's out buying and installing water hammer arresors BUT, he can't get more water without increasing his PRESSURE. Which again then increases his velocity. Following your advice, he's got a too small pipe. And going to 1" is a waste of money and time to drill out joists etc. to get it through where 3/4" galvanized was used previously. The same size PEX, CPVC or copper is the right choice pipe size. Go look it up in something other than an old book. Find flow rates of various materails. Read up on velocity and water hammer.

I said specific to the building, that's not a blanket type statement applying to all buildings.

Look, I'm replying to what you said and I know the next larger ID pipe provides 2-3 times the water volume than a 1/2" pipe given the same pressure. Telling this guy with the question Is bigger better? to go with 1/2" copper when he has 3/4" galvanized (steel) due to a change in the material is wrong.
Go here and check out the result of your 1/2" copper to 3/4" steel and see if you can visualize the additional water you get out of the 3/4" steel as compared to 1/2" copper when all esle is the same. Also check out the velocity difference and the blurp concerning velocity on the same page. http://www.connel.com/freeware/flowcalc1.shtml
And then go play around this page. http://www.geagolf.com/GEA%20Pressure%20and%20Flow.html
And if you need more information, let me know.
Gary Quality Water Associates www.qualitywaterassociates.com Bulletin Board www.qualitywaterassociates.com/phpBB2/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Gary Slusser wrote:

I didn't say that. Go back and read what I said.

Fine.
One last comment as we may be cross talking. First, my main concern was that the idea that one specific size is right, is just not correct. Larger pipe may cause other problems but it doesn't cause flow problems. Hey, it was me that said bigger is better.
Ok, so you disagree with the 1/2 copper replacing 3/4 inch iron pipe. Ok, that's fine. It really doesn't make any difference to the discussion because (a) he now has 1/2 iron pipe and you know that 1/2 copper will flow better than 1/2 iron pipe. And (b) I said that if it were my house I would use larger pipe.
I think you just want to argue. So look back through the stuff, I never said to replace 3/4" iron pipe with 1/2" copper.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Oh.... not in my opinion but let's see.
Well I see that in my mind I did have him with 3/4" galvanized going to 1/2" copper when he actually said "galvanized 1/2" to copper..."
But then I did not reply to what he said. I only replied to what YOU said and here's the basis of my replies:

So come again as to who said what. And stop arguing 'bout it. :)
Gary Quality Water Associates www.qualitywaterassociates.com Bulletin Board www.qualitywaterassociates.com/phpBB2/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
George E. Cawthon wrote:

Those "several books on plumbing" either didn't know what they were talking about, or they were having you design for 50 years later when the iron pipes *might* be full of corrosion. For a given size, copper will supply a little more water because it's smoother inside and you have less turbulence. But this affect is quickly overwhemed by the larger cross sectional area of the next size larger iron pipe.
For cold water supply lines, using a larger pipe than necessary doesn't hurt anything but it doesn't gain you much either. But for hot water supply lines, using too large a pipe will waste water and energy.
Generally speaking, 1/2" pipe can supply more than enough water for one faucet but not necessarily enough for two or three (assuming we are talking about relatively short runs inside a house, not 200' of irrigation pipe.) Whether you can supply 1, 2, or 3 with a 1/2" pipe depends on the water pressure and the flow rate of each of those faucets.
Best regards, Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
zxcvbob wrote:

Ok, so the books are wrong.

That was exactly my point, a larger size won't hurt. Larger size hot water (and cold water) supply lines may waste heat but they also reduce shower temperature variations when the WC are flushed or washing machines are operating.

Bob, my first comment said 1/2" iron was in adequate and recommended using a 1" or 3/4" copper pipe.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

George is right to a limited extent. Interior pipe smoothness _does_ have a factor in flow rates. But it's a very small one (unless the inside of the pipe is _very_ rough), so it is not an issue in practise.
Ie: not a significant factor with (new) copper versus plastic. _Might_ become an issue with copper if your water causes the copper to crud up really badly. Will often become an issue with old iron pipe installations. But in either of those cases, diameter restriction is going to play a bigger part than roughness.
Secondly, water pipe _can_ make flow noise from roughness - microturbulance, bubble formation etc. But, if the noise is only noticable at high water velocities - at velocities so high that pipe drag and thus pressure drop is unacceptable - the pipe is just too damn small in the first place - a different pipe smoothness at the same size is not going to make a detectable difference.
Aside:
Pipe drag/pressure drop has non-linear relationship to water velocity. In other words, pressure drop increases faster than GPMs in the same pipe. As I recall the "rule of thumb" (at least for irrigation systems), you should never design 1/2" lines for more than 5-7GPM, and 3/4" for more than 10-15GPM, because beyond that point pressure drop becomes very substantial. And even those flow rates will often cause annoying pressure problems on longer lines. Which is why the irrigation specialist told me "for god's sake, don't use 1/2" _anywhere_" ;-). [I cheated a bit, but only for single low flow heads.]
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The best way to determine this is to count up the max gpm of each fixture and find the flow rate of the pipe based on the pressure you have.
The best material to use should be dictated by your water quality now and what it might be in the future. There's something in your water now that has caused the galvanized to rust; will it likewise cause copper to be added to your water while eating the new tubing? Very probably if you were to learn about all the things found in water that deteriorates copper tubing. IMO copper should not be used with a pH of less than 7.0 and then the DO, CO2 and TDS content should not be more than minimal. Electrical grounding and bacteria are causes of pinholes in copper tubing also, among other things things. PEX is probably the best material for replumbing water lines bar none. Copper does not meet the NSF Standard 61 if the pH of the water will be less than 6.5. The acceptable pH used to be 6.9 to 8.5 but was lowered in 1990-'91 to get water companies to accept the Lead and Copper Rules.
Gary Quality Water Associates www.qualitywaterassociates.com Bulletin Board www.qualitywaterassociates.com/phpBB2/
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.