As a product manager in the PEX piping industry, having a comprehensive grip on the extensive range of PEX pipe sizes, dimensions, and thicknesses is essential for ensuring we offer optimal configurations aligned to customer needs. But with so many variables like materials, pressure ratings, and standards, sizing PEX products appropriately can get complex quickly. In this detailed guide, I'll arm readers with a comprehensive PEX size chart covering tube sizing conventions, dimensions, and available thicknesses. I'll also discuss how thoughtful size selection delivers superior performance and why oversizing PEX is risky. My goal is to demystify the extensive PEX size options so engineers, contractors, and system designers can zero in on the ideal tubing for their application needs.
PEX Size Designations
First, let's cover the numeric size designations used for PEX tubing. Like other piping materials, PEX uses nominal sizes which correspond to approximate inner and outer diameter dimensions. This chart shows common nominal PEX sizes and actual dimensions:
Nominal PEX Size - OD (in) - ID (in)
| Nominal Size (inches) | Outside Diameter (OD) | Inside Diameter (ID) |
|---|---|---|
| 1/4" | 0.375" (9.5 mm) | 0.25" (6.4 mm) |
| 3/8" | 0.500" (12.7 mm) | 0.375" (9.5 mm) |
| 1/2" | 0.625" (15.9 mm) | 0.485" (12.3 mm) |
| 5/8" | 0.750" (19.1 mm) | 0.584" (14.8 mm) |
| 3/4" | 0.875" (22.2 mm) | 0.681" (17.3 mm) |
| 1" | 1.125" (28.6 mm) | 0.941" (23.9 mm) |
| 1-1/4" | 1.375" (34.9 mm) | 1.169" (29.7 mm) |
| 1-1/2" | 1.625" (41.3 mm) | 1.401" (35.6 mm) |
| 2" | 2.125" (54.0 mm) | 1.877" (47.7 mm) |
As we can see, the nominal size gives a readable approximate value while the exact outer and inner dimensions of the PEX walls vary slightly. This is important when calculating flow rates or connector fittings.
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Pressure Ratings
In addition to size, understanding PEX pressure ratings is crucial for appropriate pipe selection. Pressure ratings indicate the maximum working pressure the tubing can safely withstand at 73°F water temperature before risking rupture and leakage. Standard pressure ratings include:
160 PSI – For residential cold water lines
100 PSI – For residential hot water lines
200 PSI – For commercial hot and cold lines
Higher PEX grades like PEX-A can reach pressure ratings of over 200 PSI for demanding applications. Confirm your system's pressure requirements and specify a PEX rating that provides safe overhead. Undersizing pressure capacity invites disaster.
Sizing for Demand
When selecting PEX diameters, the most important factor is fulfilling flow rate demand. Larger sizes offer less friction and impedance but cost more. Downsizing tubes save money initially but cripples flow. Balance these factors:
- Calculate the peak flow demand for each pipe run using fixture units.
- Consult PEX sizing tables to choose the minimum size satisfying expected peak flows.
- For multi-outlet branches, ensure the trunk line is at least as large as the largest branch.
- Upsizing is preferred for high-flow demand situations like laundry and bath groups.
Also, consider if pressure losses from undersized PEX will impact fixture performance. Right-sizing for actual demand optimizes costs and utility.
Matching Tube and Fitting Sizes
Another key sizing consideration is matching PEX tubing with appropriate same-sized fittings and connectors. While insert fittings allow some flexibility, using the right corresponding fitting size optimizes flow.
- For barb fittings, use the same nominal size for both pipe and fitting.
- Compression fittings should align diameter-to-diameter with the tubing.
- With crimp fittings, use matching ODs but the ID can downsize after crimping.
Mismatched tube and fitting sizes often create leaks, flow issues, and connection failures.
Tube Wall Thickness
PEX wall thickness is also an important parameter impacting pressure capacity. Thicker walls increase strength but reduce inside diameter. Common PEX wall thicknesses are:
SDR-9 = 0.132" – The thickest/strongest residential PEX tubing
SDR-11 = 0.109" – Standard thickness for residential use
SDR-13.5 = 0.092" – Common thickness for commercial PEX
SDR-15 = 0.8" – Used in some commercial and hydronic applications
The Stronger SDR-9 is preferred for cold water lines and high-pressure applications. SDR-11 can be used for most residential hot and cold lines. SDR-13.5 suffices for commercial hot and cold supplies. Go thicker rather than thinner where high pressures are expected.
As product managers, it is our responsibility to arm designers, engineers, and installers with the full understanding required to maximize PEX capabilities for each unique application. I hope this thorough examination of the many intricacies of PEX sizing provides the comprehensive details needed to specify plumbing that aligns with both building realities and customer needs. Please reach out with any additional questions on navigating the extensive but nuanced world of PEX sizing selection. I'm always glad to help unravel the complexity to achieve fluid operations.
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