Direct answer: 16×2.0 has a nominal inside diameter of 12.0 mm and 17×2.0 has 13.0 mm — the two are not wall-thickness variants of one pipe but separate size families. Choose in four steps: design calculation, connection system, installation method and release check — not by assuming the larger outside diameter is automatically better.
- The marking reads outside diameter × wall thickness in mm: 16×2.0 → 12.0 mm bore; 17×2.0 → 13.0 mm bore.
- The flow-area ratio derived from the stated dimensions is (13/12)² ≈ 1.17 — a geometric derivation, not a measured flow conclusion.
- 16×2.0 is more common in cross-linked polyethylene coil systems and 17×2.0 in multilayer / aluminium-plastic coil systems — a market observation, not a rule for every product.
- Fittings, seals, pressing tools and manifold interfaces of the two size families must not be assumed interchangeable.
- A release check covers at least outside diameter, wall thickness and tolerance, coil length and net weight against the order and the grade specification.
What the two numbers mean
The first number is the nominal outside diameter and the second the nominal wall thickness. Reading the marking correctly prevents treating 17×2.0 as a thicker-wall version of 16×2.0: the bores differ by 1 mm, and actual dimensions, tolerances and minimum bend radius must be confirmed against the grade-specific technical sheet and inspection report. One millimetre sounds small, but flow area scales with the square of the diameter — at equal conditions the 17×2.0 cross-section is about 17% larger, with correspondingly lower velocity and friction loss. The ratio comes from dimensions alone; real pressure loss also depends on water temperature, circuit length, bend count and temperature spread, and must be confirmed by design calculation.
Why two size families exist
Different markets and product traditions produced different size families. 16×2.0 is more often seen in cross-linked polyethylene coil systems, 17×2.0 in multilayer or aluminium-plastic coil systems; they are not two wall-thickness options within one family. Three practical consequences follow:
- Fittings and manifolds are not interchangeable: a 17 mm pipe must not be paired with 16 mm pressing dies, seals or manifolds; mixed systems are a common field failure source. Confirm the complete pipe-and-fitting combination before ordering.
- Bending feel differs: a multilayer pipe with an aluminium layer generally holds its formed shape with less spring-back, while an all-plastic pipe recovers elastically and needs more clips or fixing support. The result depends on product construction and installation conditions.
- Spare-part ecosystem: distributors should select the pipe size that matches the fitting system they already stock, not the one that merely looks thicker.
Installation: spacing sets the density, not the diameter
Within one room, circuit spacing comes from hydraulic design: tighter spacing raises output per area, wider spacing serves lower-load zones, and both can coexist in one system. Spacing is a design input; it is not decided by choosing 16×2.0 or 17×2.0. Treating a larger diameter as a substitute for proper spacing skips the actual hydraulic calculation — fix the design first, then the size.
Four-step selection path
- Design first: circuit length, supply/return temperature difference, heat output per area and allowable pressure loss should be resolved by hydraulic design before the material is fixed.
- Then the connection system: which size family do the existing manifold, control valves, pressing tools and seals support?
- Then the installation method: wet screed tolerates spring-back; dry panels and thin-layer systems are more sensitive to shape retention and minimum bend radius.
- Finally the release check: measured outside diameter and wall thickness with tolerances, coil length (with tolerance), and net weight — the most reliable proxy for coil length — must match the order and the grade specification.
| Item | 16×2.0 | 17×2.0 | Why it matters |
|---|---|---|---|
| Nominal OD × wall | 16 × 2.0 mm | 17 × 2.0 mm | Read the marking before comparing |
| Nominal bore (geometric) | 12.0 mm | 13.0 mm | Outside diameter − 2 × wall thickness |
| Flow-area ratio (geometric) | 1.00 (reference) | ≈ 1.17 | Derived from stated dimensions, not measured flow |
| Common system family | PEX coil systems | Multilayer / aluminium-plastic coil systems | A market observation, not a rule for every product |
| Fittings / dies / manifolds | Own size family, not shared | Own size family, not shared | Mixing is a common field failure source |
| Bending feel (typical) | All-plastic: clear spring-back, more clips | Aluminium layer: holds shape, less spring-back | Depends on construction and site conditions |
Scope and boundary
This page is a specification-reading and release-check framework, not a substitute for hydraulic calculation; the area ratio is a geometric derivation only and is not a system performance promise. Design should follow the applicable edition of EN 1264 and destination-market requirements. The system-level 16-versus-20 discussion (circuit capacity, pressure loss, loop configuration) is a separate topic and is not covered here; see SDR, PN, wall thickness and common diameters for how to read the standards and the underfloor-heating pipe range for product dimensions.
Frequently asked questions
Is 17×2.0 always the better choice?
No. It offers a larger nominal bore on the stated dimensions, but the suitable option depends on design calculations, the existing connection system, installation method and verified product data.
Can a 16 mm fitting be used with a 17 mm pipe?
Do not assume so. Confirm the fitting, seal, pressing tool and manifold as a matched system for the selected size family — wall thickness looking similar is not compatibility.
Does the area ratio prove a flow or pressure result?
No. It is a geometric derivation from the stated dimensions, not a measured flow conclusion. System results require project-specific calculation and verified inputs.
Which documents should be checked before release?
The order, grade-specific technical sheet, inspection report, dimensional tolerances, coil-length information and the compatibility of the proposed fittings and tools.
Data boundary
The bore and area ratio are geometric derivations from the stated dimensions; no statistical period or measured sample applies to this page. Actual dimensions, tolerances, minimum bend radius and system performance follow the grade-specific technical sheet, inspection report and project design. The system-level 16-versus-20 comparison is not included.
Sources
- EN 1264 (design and installation of embedded heating and cooling systems) — official CEN edition (retrieved 2026-10-01).
- EN ISO 21003 parts 2/3/5 (multilayer pipes / fittings / fitness for purpose) — ISO catalogue (retrieved 2026-10-01).
- ISO 15875 (PE-X), ISO 22391 (PE-RT) — ISO catalogue (retrieved 2026-10-01).