Key points to selecting a PEX piping system design

Selecting the most appropriate plumbing system design for a home can be a challenge for the plumbing designer and builder. The unique properties of PEX piping allow it to be configured in a number of different designs. All have been shown to work well in residential applications, and all are code approved. Depending on the design of the home, each has different performance characteristics, installation costs, material costs, and ease of installation.

The selection of a system design is generally based on a combination of key factors such as material cost, labour time, ease of installation, system performance, and installer preference. The challenge for a plumbing designer is to select the system that balances the unique needs of the installer, homeowner, and builder. The following comparison of the three most prevalent PEX plumbing systems, trunk and branch, parallel, and zone, provides some guidance. Selecting one of the three systems described is not hard and fast, and often involves a balance since each project, installer, and circumstance is different.

Fortunately, there is no wrong choice. All three system designs will supply sufficient flow and pressure to the outlets even when the base riser pressure is 40 psi and the length to the farthest outlet is 100 ft. But, the costs and performance of each system do vary for each house design. Selecting the best system can reduce installation costs, minimize installation headaches, and lead to more satisfied homeowners.

To aid in the decision-making process, several tools are provided in Design Guide Residential PEX Water Supply Plumbing Systems, including general rankings of the systems for key factors, layout examples, performance testing and industry technical support. General rankings of the systems for key factors, featured here, provide a place to start and compare how the systems stack up based on your priorities.

 

General rankings of the systems for key factors

The general characteristics of the systems are ranked in Table 1. Given the differences between housing designs and preferences, they may not apply in every situation, but are useful for general guidance. The best way to use Table 1 is to establish the relative priority of key factors, and use the rankings of system designs as a starting point for the system to be selected.

For example, if when considering the factors in Table 1, you determine the top three factors are: minimizing fittings and joints1; centralized shut-off valving; and pressure stability with use of multiple fixtures. With the parallel system ranking at the top of all three, it is a logical place to start. If your top factors result in three different best designs, the right choice is not as obvious. You will then need to consider other factors, and further explore the detailed design of the home.

Cost has been omitted as a factor in the Guide. Since local labour costs vary, and there is variation between the fitting and piping costs offered by different manufacturers, the guide provides information on the amount of pipe and fittings needed. The determination of actual cost estimates and total cost comparison between system designs is left to the designer or installer.

An appropriate balance between labour and material costs as well as the relative performance of the systems is important when deciding on a system layout for a particular house.

 

Example layouts

The residential plumbing system layouts shown here provide estimated fittings and piping descriptions for two common house types: colonial and condominium (the complete Guide also includes ranch and townhouse styles). Piping lengths, and fitting and joint counts are provided for each system to provide a comparison of material use and labour required. Select the home design that most closely resembles your design to help select the appropriate system for you. Note that in these designs, few obstructions are accounted for and thus represent idealized pipe runs with a minimum of fittings. Table 2 outlines the number and type of fixtures for each house.

Colonial house layout

The colonial house layout has approximately 2,000 sq. ft. of floor area. The water main enters the house under the unfinished basement slab. The water heater is located near the main water line in the basement. The first floor has a living room, dining room, kitchen, family room, and a powder room. The second floor has four bedrooms, two full baths, and the clothes washer.

 

In home layouts with a large separation between fixtures, the trunk and branch design has the least pipe followed by the zone design. The parallel system uses the most piping (1.8 times more on average) and the least fittings and joints. Although the parallel system uses more piping, the smaller diameters are easier to handle and install, particularly around bends.

 

Condominium layout

The condominium has approximately 1,200 sq. ft. of floor area. It has a living room, kitchen, dining room, two bedrooms, and two full baths. The clothes washer is located in the unit. The building has a central plant for water heating; therefore, there is no water heater located in the unit. The trunk and branch system uses the most tees, which increases the number of joints. The trunk and branch and zone system layouts are similar in pipe use, but the zone system uses fewer fittings resulting in fewer joints. The parallel system uses the most pipe (1.8 times more on average) and the fewest fittings. Again, the parallel system uses more pipe with smaller diameters.

The trunk and branch system uses the most tees, which increases the number of joints. The layouts are similar in pipe use but the zone system uses fewer fittings resulting in fewer joints. The parallel system uses the most pipe (1.8 times more on average) and fewer fittings. The parallel system uses more pipe with smaller diameters.

X