Plumbing for the Future

Building a high-performance house? Consider this piping layout that capitalizes on the flexibility of PEX pipe and the efficiencies of multiport tees located near fixture groupings.

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I recently had a conversation with an engineer who was planning his retirement home. He is going all out with sustainable design and thoughtful products to ensure decades of dependable, comfortable, energy-efficient use, along with strong resilience in a hurricane-prone region.

His design includes the use of insulated concrete forms (ICF construction), self-consolidating concrete that provides R40 insulation, Pella Architect Series windows and doors, steel roof trusses, and reflective metal shingles with an air barrier to keep the roof deck and attic cool in the hot summers.

After learning about all this impressive, sustainable design, he sent me the plans for his plumbing system. The standard trunk-and-branch design was typical for a traditional home. However, this home was anything but traditional.

I told him about Logic Plumbing design. This is a piping layout that capitalizes on the flexibility of PEX pipe and the efficiencies of multiport tees located near fixture groupings. The design uses significantly fewer connections compared to trunk and branch while also requiring much less pipe compared to a homerun layout. Best of all, it maximizes hot-water delivery times and minimizes water and energy waste.


Logic Plumbing Design

The heart of Logic Plumbing design is the multiport tee—a long tee with multiple outlets. However, it’s not considered a manifold, so there is no requirement for access behind a wall.


The innovative design of the multiport tee adds to installation and performance efficiencies. For example, six regular tees require 18 connections (three connections for each side of the tee). However, a flow-through multiport tee with six outlets needs only eight connections (six connections for the ports, a main flow-through inlet, and a main flow-through outlet). Multiport tees also require less space to install since there is one, compact multiport tee instead of multiple individual tees.

Multiport tees are made of engineered polymer (EP), a thermoplastic material that has superior mechanical, chemical, and thermal properties that provide dimensional stability in demanding applications, including areas of high stress, heat, and moisture. The multiport tees are also a perfect pairing to PEX pipe since both resist pitting, corrosion, and scale buildup, and both are approved for direct burial in the soil or concrete slab.

Logic Plumbing Efficiencies

Here’s where Logic Plumbing really makes sense. Take, for example, a 2,300-square-foot, two-story home. A Logic Plumbing design requires only 637 feet of pipe, while a homerun system uses 1,515 feet of pipe.

All that extra pipe can lead to issues isolating hot- and cold-water lines, increasing heat transfer and energy inefficiencies within the plumbing system. The added pipe can also mean reduced water pressure and longer wait times for hot water to arrive at the fixture. 

A Logic Plumbing layout provides faster hot-water delivery and reduced pressure loss for a higher-performing system. And while it’s true a Logic Plumbing design uses slightly more connections than a homerun layout (59 vs. 48 in the 2,300-square-foot, two-story home example), the amount of pipe savings is significantly more beneficial.

Comparing Logic Plumbing to trunk and branch, there is a substantial difference in fittings usage. Again, using the two-story home example, a Logic Plumbing design uses only 16 fittings and 59 connections compared to 96 fittings and 165 connections for trunk and branch. These added connections greatly limit system performance with increased pressure loss and can also increase potential leak-point liability.

Hot-Water Benefits

One more important point to note about multiport tees—they offer significant advantages for clustered or consecutive uses of hot water. Once hot water arrives at a multiport tee, it is readily available to all fixtures connected to that tee. Essentially, that multiport tee’s fixture grouping is “charged” with hot water.

For homerun systems, hot water is not necessarily readily available for clustered uses that occur at faucets other than the original (first use) fixture. The hot water is available only at the central manifold. The system must still deliver hot water all the way from the manifold to the faucets where subsequent clustered uses are taking place.

Using multiport tees is also advantageous for hot-water recirculation systems because it’s easy to install recirculation “loops” that return water to the heater. This is not as easy with a homerun configuration where recirculation can typically be done only between the central manifold and the water heater, but not between the fixtures and the water heater (because it would be necessary to recirculate from each fixture).


PEX and Logic Plumbing Resources

To learn more about Logic Plumbing design, check out this webpage and video. To learn more about residential PEX plumbing systems, visit, the Plastics Pipe Institute, or the Plastic Pipe and Fittings Association