Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[DUNBAR PLUMBING]

This question was asked to me regarding a piping question:


Hi,

I've read quite a few of your posts and you really seem to know what you're talking about. I was hoping you could provide me with some advice:

My 1939 house has all galvanized steel supply piping and is 28'x24'. The house has two full baths, a water heater, kitchen (w/ dishwasher), and a washer. I would like to replace the horizontal runs to which I have easy access in the basement (i.e. not the vertical runs up in to the stud cavity). I'm not clear, however, on how I should go about sizing the new copper pipe.

All of my water pressure is fine now, so I'm not seeking to improve the system at all, just swap the steel for copper. However, the OD of the main steel supply is ~1.5" (hard to measure without cutting it) and the sizes vary from there from ~1" to ~3/4". I can't imagine I need copper that big, so my question is: is there a rule of thumb when changing from steel to copper? Perhaps replace all the 1.5" with 3/4" the 3/4" with 1/2" and so on? Is there a way for me to determine the ID without cutting open the pipes?

Or, is it safe to say that from the main valve, running 3/4" ID copper and branching to 1/2" for each fixture would be ok?

Also, if I run 3/4" cold from the main to the water heater, is it still ok to run 3/4" hot water off of the heater (branching to 1/2" at each fixture)? Or would this mean that the hot water system could, theory pull the full 3/4" flow all the way from the main, causing cold water pressure problems? In other words, should the hot water line coming off the water heater be smaller than the main line?

Any help, and any other advice on the switch over is greatly appreciated! Thank you so much!
 

[DUNBAR PLUMBING]

Our response,





On your plumbing situation,


The national "trend" is usually as follows:



3/4" copper from the meter/street curb to inside the house, in and out of the water heater and then branch down to 1/2" on the last 3 hots, last 3 colds.


You can make lateral branches off that 3/4" line along the way to serve nearby fixtures, but always remember that you cannot serve more than 3 fixtures on 1/2" pipe, otherwise you'll be undersupplying the fixture.


In all my years as a plumber I've never had a need to go above 3/4" piping, since on the residential front there isn't much more than 3.5 baths in most cases.

If the distance from your house to street is significant, then it would be ideal to have a larger main line. But I'm speaking in the 100's of feet to accomplish that.

Hope this helps.


Steve

[Tags:]

Tags: water piping  water pipe sizing  copper pipe  water line installation