Piping Materials: Just the Basics

I’m a regular reader of pme and was hoping you could provide me with some basic information piping materials. What is the main difference between PP-R, PEX, CPVC, and aluminum-reinforced PVC? Do you have some length guidelines for attaching the small pipes to walls? Thank you for considering my questions.

Emo Benoit
Veolia Water Asia
Shanghai, P.R. China

Julius Ballanco responds:
The difference is that they are different plastics. PEX is considered flexible. PP is considered semi-flexible. CPVC and PVC are rigid pipe. As for hanger requirements, rigid plastic pipe has a spacing requirement of four feet for hangers. Flexible plastic pipe has a spacing requirement of 32 inches.

Ground Joint Unions - Gas Systems

Recently, I noticed two ground joint unions within the runs of the gas system pictured here (Nov. 08, page 53).  It has been my understanding that unions were permitted just before an appliance. If it was necessary for a union at these locations, I have always used a “left and right” nipple and coupling. Has there been a code change?

Dan Thompson

Julius Ballanco responds:

There hasn’t been any code changes regarding unions. The unions are permitted to be installed in these locations. However, the code still does not permit unions to be concealed unless they are so listed. For the installation in the photo, no finished ceiling was to be installed. This was a basement area with an open ceiling.
I realize that the building owners could decide to finish the ceiling at a later date. At that time, the fitting would have to be addressed regarding this issue. I hope this helps.

Multipurpose Fire Sprinkler Systems

I recently was given an older article on multipurpose residential fire sprinkler systems (Nov. 2007). As a fire protection engineer for almost 35 years, I read it with great interest. I must commend the author, Alan Larson, CET, CFPS, for his excellent presentation of this vital information on the proper design of a multipurpose residential fire sprinkler system in accordance with NFPA 13D, “Standard for the Installation of Sprinkler Systems in One-and Two-Family Dwellings and Manufactured Homes.”

However, I would like to correct one statement that was stated as a fact, but is clearly a misconception of the requirements under the Plumbing Codes. On page 43 of the magazine, the author provided a “…simple diagram of a looped multipurpose system…” The statement under this diagram said, “Piping must be installed with no dead ends to ensure a non-stagnant system.” This statement is not correct.

It was never the literal text, or the intent, of NFPA 13D or the Plumbing Codes to prohibit multipurpose residential sprinkler systems on the typical “tree branch” piping layout (i.e., having either sprinklers or other plumbing fixtures at the end of the branches). Looped systems are great for reducing the pressure loss to a sprinkler or other plumbing fixture, but looped systems are not required for either standard plumbing fixtures or multipurpose sprinkler systems.

It is very typical to design plumbing systems in homes, as well as other occupancies, to provide “fit-outs” for “future plumbing needs” such as future “powder rooms,” “wet bars,” “basement kitchens,” etc. Even in high rise and other large commercial buildings, the addition of unused “wet stacks” are commonly provided for potential future needs and may stand for years before being “tapped onto,” if used at all. How many of your readers have “hose bibs” in their homes that are at the extreme end of their house plumbing system that may be used once or twice a year, or not at all for years?

Stagnant water in a branch line in a code complying portable water system designed in accordance with NFPA 13D or the Plumbing Codes may not taste “good” because of the oxygen depletion of the “sitting” water, but it is not in any way considered a health hazard or a violation of the Plumbing Codes.

Dead ends for future “fit-outs” or future “wet stacks” are common in plumbing systems, and their potential use in residential multipurpose sprinkler systems should present no health or code issues over what is already permitted by the Codes.

Thank you for the opportunity to clarify this important issue.

Marshall A Klein
Marshall A. Klein & Associates, Inc.
Eldersburg, MD


A couple errors appeared in the Nov. 2008 article, “Back to Basics: Sizing Gas Piping Systems.” On page 62, third column, first full paragraph, the number 210 should have been 220. In Figures 2 and 3 on page 70, the number 210 should have been 220, and 145 should have been 155. Pme regrets the errors.