Linear expansion of copper, steel, PEX and PP-R
ΔL = α · L · ΔT with α 16.6 (copper), 12 (steel), 140 (PEX) and 150 (PP-R) × 10⁻⁶ /K. Pick the material, type the length and the temperature rise.
Limits and citations come from the app's pack files. The calculator below is checked against the app's engine on every build · engine 1.
The same job in the app
10 m of PEX warmed by 40 K grows 56.0 mm.
How it's calculated
ΔL = α · L · ΔT: the growth is the expansion coefficient times the length times the temperature rise. Plastics move roughly ten times as much as metals, which is why a PEX run that looks short still needs somewhere to go.
When the growth is large enough to matter, the app says so and suggests an expansion loop or a check of the clip spacing on straight runs.
Worked example
10 m of PEX warmed by 40 K: 140 × 10⁻⁶ × 10 × 40 = 56.0 mm. Allow a loop.