# Copper pipe size question



## greymous (Jan 27, 2009)

Sorry for the stupid question but I did not find an answer using the search feature.

I've got old steel pipes in the basement that I'm going to replace with copper. In looking around the internet I see that most of the diagrams use 3/4" pipes at first then switch to 1/2" pipes when they go upstairs. 

Is there a reason to switch to smaller pipes (other than increased pressure)?

Thanks,
Ken


----------



## jporter5333 (Jan 27, 2009)

By upstairs, do you mean a second story upstairs or just through the floor from the crawlspace/ basement to a fixture?


----------



## PLUMBINGITALL (Jan 25, 2009)

If you are talking about going from 3/4 to the fixture with 1/2; It is done to put a 1/2x3/8 stop on it. And then use a lav or toilet supply to the stop. Just for info the pressure does not increase by going to a smaller pipe. The pressure would be the same but the volume is decreased.


----------



## jporter5333 (Jan 27, 2009)

What PLUMBINGTALL said. I would recommend running a 3/4 trunk and then branching off with 1/2 to the fixtures.


----------



## Nestor_Kelebay (Jun 17, 2008)

Ken:

The most obvious reason for using 3/4 inch copper piping is that the inlet and outlet to the water heater are 3/4 inch in size. So, plumbers will typically connect to the water heater with 3/4 inch piping.

I agree with the previous posts about using 3/4 inch copper piping THROUGHOUT your house, and branching off to each plumbing fixture with a 3/4 X 3/4 X 1/2 inch tee. That way, the supply piping can provide full flow to two different plumbing fixtures simultaneously. That means your shower won't change temperature when someone flushes the toilet.


----------



## greymous (Jan 27, 2009)

*Thanks much! And another question.*

Thanks everyone for the responses!

What got me curious was the pipe changes from 3/4 to 1/2 about 10 feet before it makes the turn up to the kitchen sink. Just seemed strange to change it there and not further along (or behind the sink). The other set of pipes going to the bathroom (on the 2nd floor) go up through the wall as 3/4.

New question: Looking at pipe types I see that there are "M", "L" and "K". I don't think I need to worry about "K" as from what I've read that is for outdoor use. For what I am doing (replacing old steel pipes in the basement) should I use "L" or "M"?

Are there elbows and connectors specific to "L" or "M" or are they generic.

Thanks again!
Ken


----------



## jporter5333 (Jan 27, 2009)

Greymous,
The fittings are generic as far as i know. In 13 years I've never seen a fitting marked with k,l, or m. The difference in each is the thickness of the wall of the pipe. I prefer to use type L but I am a commercial guy and it is generally required on any job I do. I use it on houses as well though. The main reason to use "m" is that it is a little cheaper than L so it gets used alot in residential to keep cost down and it will work fine.


----------



## greymous (Jan 27, 2009)

Thanks jporter!

If the price difference is not too bad (I'll need about 110' of pipe) I'll probably go with "L" as I'd rather use better quality to begin with.


----------



## Maintenance 6 (Feb 26, 2008)

Type "M" is supposed to be used for low pressure spplications like heating systems. I'd never use it for domestic lines. The fittings are the same. As far as pipe size, a larger line will carry more water with less pressure drop. A 3/4 line will carry the same volume as 2-1/2 half inch lines will at the same pressure. That means exactly what Nestor said, flushing the toilet won't have as much impact on the pressure in the shower if they are fed from a 3/4 supply. Just keep in mind that for hot water lines, if you use a 3/4 supply, you'll need to run that much more water until you get hot water to the outlet. And when you are finished there will be that much more water laying in the pipe that you've paid to heat.


----------



## greymous (Jan 27, 2009)

Thanks for the info Maintenance 6!


----------



## jporter5333 (Jan 27, 2009)

Not trying to start an argument but type m is fine for water distribution systems such as hot and cold domestic water. It is rated at over 300psi. But I do believe like we've all said that L is the better choice and it should be used unless you jusst can't afford it.


----------



## brokenknee (Dec 13, 2008)

I really don't see the advantage of using L piping, IMHO it is just more costly. M has been used in residential plumbing for years. The weak points in any plumbing job is usually the solder joints, if you have good joints you should not have a problem. I have exposed plumbing in my laundry area that has been bumped and hit for years with no problems.

I am not sure were you are located but if freezing pipes is your concern then none of the three types are rated for freezing and they will all rupture. I know as I did a repair for a friend who thought if he used L piping to an outside faucet he would not have to worry about it freezing.

I would also consider pex piping, you will have some up front cost for some specialty tools. But once you have them your good to go. Working with pex is a breeze. You can buy it at the local home center in 500' lengths. The fittings are a little more costly but when you factor in you use fewer of them you are usually money ahead. 

Pex pipe can freeze and not burst, however the fitting will.

I want to state as the previous poster said about starting an argument. I do not want one. The opinions I expressed here are solely my own.


----------



## Nestor_Kelebay (Jun 17, 2008)

Brokenknee:
I agree that either Type M or L would work. Typically, Type M is used in homes and Type L in commercial applicaitons.

If it were my own house, I'd use Type L because it has a thicker wall. I've had several times when copper pipes have gone out of round on me, and every time it was a Type M pipe. The Type L is simply stronger because it has a 0.040 inch wall thickness as opposed to 0.028 inch for Type M (and 0.049 for Type K). That's more than a 33% increase in wall thickness over Type M, and that makes for a stronger pipe, even when hot at soldering temperatures.

If it were easy to change the type of copper pipe, it wouldn't matter. But since the lion's share of the cost of replacing the piping is going to be the cost of the labour, I'd opt to pay a few percent more on the total job cost and go with the Type L piping. It's going to change the cost of the job very little, but it'll make a big difference in the quality of the finished product.


----------



## brokenknee (Dec 13, 2008)

Just curious, when you say gone off around you what do you mean? Are you saying the pipes ruptured? If it were a leak in the joint I do not think it would mater if the pipes were M or L, a bad solder joint is just that and will leak no matter how thick the pipe is.

I installed residential water softeners for about a year full time and a couple years part time after that. In all my installs that had copper pipe I do not recall one time any of the homes had type L copper in them. (I really enjoyed working on the old galvanized piping :laughing

I do not disagree that type L is a stronger thicker pipe, I just do not see the need for it in residential plumbing. The plumbing in my home is 23years old (I had the house built) The only problem I have had is one joint starting to leak. I cut it out and sweated in a new fitting, never have I had any other problems.

I know most, if not all of the builders in this part of the country have gone to pex for new home construction. I am aware they had some problems with one manufacture of the fittings when it first came out, but that has been resolved (not necessarily the pending litigation). With the price of copper, pex is now competitive cost wise and when you factor in the cost of the labor/time saved on installation in my mind it is the clear winner.


----------



## micromind (Mar 9, 2008)

One disadvantage to using 3/4" everywhere and branching off with 1/2" is when you let the hot water run until it gets hot at the faucet, you'll waste a lot more hot water with 3/4". 

When I built my house 12 years ago, I used type M everywhere except under the footing. It's 2 story, and on a well. I used 1" from the well to the water heater, then 3/4". I went down to 1/2" to feed the last 3 fixtures in the line. 

This occurred in two places, both bathrooms. 1/2" feeds a shower, toilet, and sink. If I'm in the shower and another person flushes the toilet or washes their hands in the sink, I feel no water pressure or temperature change at all. 

The key here is to keep the 1/2" runs short, and plan it out to minimize the number of 90's.

Rob


----------



## Piedmont (Nov 1, 2007)

Here type L is required for any domestic water use, M can only be used in heating systems (someone else stated similar perhaps we live in the same state). I would go with type L regardless, my house is 40 years old and the copper pipes are failing I've been replacing them with type "L" (which is required here anyway, and possibly my area eats copper and why L required). 

The short answer about the 3/4" or 1/2" thing has to do with the velocity of the water (how fast it runs through the pipes). With all fixtures turned on to a branch the velocity of the water in the pipe must flow under 8 fps, anything more and the water flows so fast it starts scraping the copper pipe rapidly shortening life. 

A 1/2" pipe can usually supply enough water for 3 fixtures keeping velocities under 8fps... which is typically a single bathroom (shower,toilet,faucet). If your upstairs has 2 bathrooms you need 3/4" feeds but only need 1/2" branches off it to each bathroom. 

A bathroom with 4 fixtures (toilet, shower, 2 sinks). The cold line has to be 3/4" coming in since cold supplies all 4 fixtures (toilet, shower, 2 sinks) the hot only needs to be 1/2" since it only feeds 3 fixtures (it doesn't feed the toilet). 

3/4" pipe can only feed 6 fixtures, so an upstairs with a full bathroom with 2 sinks (4 fixtures) and a full bathroom off the master bedroom (another 3 fixtures) would require a 1" cold water feed and 3/4" hot. Confused yet!? :huh:

1/2" pipe can typically supply water for up to 3 fixtures.
3/4" pipe can typically supply water for up to 6 fixtures.

It's okay to use 3/4" and branch off to 1/2" as long as there isn't more than 3 fixtures on each 1/2" branch or more than 6 fixtures in total the 3/4" feeds.

I have no idea about PEX.


----------



## brokenknee (Dec 13, 2008)

If required by code, then that is what you should use regardless of your opinion. Codes are put in place for a reason.

I googled copper history and found,

"Corroding copper tubing has been reported in cities as far apart as Phoenix, Arizona;
Andover, Massachusetts; Santa Clarita, California; Lima, Ohio; Washington, DC; and Jacksonville, Florida."​ 
Something to do with low PH levels in the water. 

If pex is permitted by code in your area, I would look into that. 

Edit: life expectancy of copper pipe was rated from 25 to 40 years. It made no mention of the type of copper it was rating.

I have no affiliation with any company or anyone that has anything to do with pex. I have just started using it and IMHO it is the best thing since sliced bread in plumbing.


----------



## Nestor_Kelebay (Jun 17, 2008)

> Edit: life expectancy of copper pipe was rated from 25 to 40 years. It made no mention of the type of copper it was rating.


C'mon man. Let's be keeping it real in dis place here.

Copper piping became the norm during the 1950's. My apartment block was built in 1960, and it has copper piping for all the domestic water. Ditto for my father's building built in 1961. One sister has a house built in 1972 and the domestic water supply piping is all copper. My other sister has a house built in 1978 and also has copper piping throughout.

So far, ONE pinhole leak in a copper pipe that seemed to be in place when the concrete floor was poured around that pipe in a laundry room. I suspect that pin hole leak may have been a matter of highly alkaline concrete being in contact with the outside of the copper, and the pin hole leak forming on the outside of the pipe, not the inside.

Also, those copper pipes removed from my building showed no signs whatever of corrosion or damage or pin hole leaks forming in them. (Whenever I would renovate a bathroom, I would remove the Type L copper pipe going up to the shower head and replace it with a piece of Type M since this pipe is only under low pressure when someone is having a shower.)

I contend that my experience with copper piping is TYPICAL, and that your suggestion that copper piping typically only lasts 25 to 40 years needs a reality check. Typically, the copper piping in new farm house 20 miles out of town will last the entire life of the house and will be salvaged for it's scrap metal value once the house is bulldozed to make way for a new shopping center. If copper piping only lasted 25 to 40 years, then on average, people would be replacing their home's copper piping as often as they replace their kitchen stove. In fact, in almost all cases, the copper piping in a house is never replaced.

You don't need to know the rest:

Why does copper last so long? With the exception of noble metals like gold and platinum, essentially all metals rust. However, for most metals like nickel, chromium, aluminum, titanium, tungsten, hafnium, etc. the oxide film they form is impermeable to oxygen, so the formation of an oxide film stops the metal from further "rusting". This is why stainless steel doesn't rust; it has sufficient chromium and nickel in it that the oxide film that forms over that steel is impermeable to oxygen. Stainless steel DOES have an oxide film over it, but it's so thin that it's invisible. (Just like low-e window glass has a film of silver about 70 atoms thick on it, but that layer of metal atoms is so thin as to be almost invisible.)

Copper oxide is only highly impermeable to oxygen molecules. So, as the copper oxide film forms, it better and better protects the underlying copper from further oxidation. This is why brand new pennies are the orangey gold colour of copper but 20 year old pennies are brown in colour, and 100 year old pennies are indistinguishable in colour from 20 year old pennies. And, it takes an imperceptible amount more sanding to sand the brown oxide surface layer off a 60 year old copper pipe than a 20 year old copper pipe, not three times as much sanding.

It's the oxide film that forms over copper that protects it from rusting and corroding when exposed to air and water with dissolved oxygen in it.

Iron (and steel is nothing more than iron with a small amount of carbon in it) is actually a rarity. Iron forms an oxide film that doesn't stick to the metal and is highly permeable to air and water. As a result, iron will rust until there's nothing but iron oxide remaining. However, iron and steel are so common in our society that we think it's common for metals to rust, oxidize and corrode away till there's nothing left. That's wrong. Most metals form oxide films on their surface, and most of the time that oxide film protects the metal from corroding further. Iron is simply an extremely common exception to that rule.


----------



## brokenknee (Dec 13, 2008)

This is were I got my information, page two http://restoremypipes.com/adf2/pdf/history_of_copper_piping.pdf

I am sure it has to do with a nation wide average or maybe even a worst case scenario; in areas with low ph levels, corrosion is more of an issue.


----------

