DWV Vent-Stack DFU / Length Check

Pass/fail of a vent stack against the adopted code's permitted DFU and developed-length table values.

Run the calculator

Example

You enter

Vent nominal diameter (in) 2
Connected drainage fixture units (DFU) 18
Developed vent length (ft) 90
Table-permitted DFU for this diameter 24
Table-permitted max length (ft) 120
Served drain diameter (in, optional) 3

You get

Length used (%) 75
Length margin (ft) 30

Checked against published worked examples from: IPC Chapter 9 / UPC Chapter 9 vent sizing (table values user-supplied).

Details, formula, and sources

ScopeThe percent of length used, the remaining margin, and a vent-at-least-half-drain check.

Formula or tablePass if connected_DFU <= table_DFU AND developed_length <= table_max_length. Percent length used = developed_length / table_max_length * 100. The vent should be at least half the drain diameter.

Source and editionPer the adopted plumbing code's vent sizing and length provisions (IPC Chapter 9 / UPC Chapter 9, by name); table values user-supplied.

Free accessCode library free read-only at codes.iccsafe.org; the AHJ-adopted edition governs.

What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.

API field namesvent_dia_in, connected_dfu, developed_length_ft, table_dfu, table_max_length_ft, drain_dia_in, length_used_pct, length_margin_ft

Table values permitted DFU and maximum developed length user-supplied from the adopted code tableIPC/UPC Chapter 9