---
kind: "section"
citation: "42 U.S.C. § 7423"
title: "42"
title_heading: "The Public Health and Welfare"
number: "7423"
heading: "Stack heights"
release: "119-102"
date: "2026-07-12"
url: "https://uscodex.org/usc/42/7423"
units:
  - "Chapter 85 — Air Pollution Prevention and Control"
  - "Subchapter I — Programs and Activities"
  - "Part A — Air Quality and Emission Limitations"
---

# §7423. Stack heights

- (a) **Heights in excess of good engineering practice; other dispersion techniques—** The degree of [emission limitation](/usc/42/7602.md?p=k) required for control of any [air pollutant](/usc/42/7602.md?p=g) under an [applicable implementation plan](/usc/42/7602.md?p=q) under this subchapter shall not be affected in any manner by—
  - (1) so much of the stack height of any source as exceeds good engineering practice (as determined under regulations promulgated by the [Administrator](/usc/42/7602.md?p=a)), or
  - (2) any other dispersion technique.

  The preceding sentence shall not apply with respect to stack heights in existence before December 31, 1970, or dispersion techniques implemented before such date. In establishing an [emission limitation](/usc/42/7602.md?p=k) for coal-fired steam electric generating units which are subject to the provisions of [section 7418 of this title](/usc/42/7418.md) and which [commenced](/usc/42/7479.md?p=2-A) operation before July 1, 1957, the effect of the entire stack height of stacks for which a [construction](/usc/42/7479.md?p=2-C) contract was awarded before February 8, 1974, may be taken into account.

- (b) **Dispersion technique—** For the purpose of this section, the term “dispersion technique” includes any intermittent or supplemental control of [air pollutants](/usc/42/7602.md?p=g) varying with atmospheric conditions.
- (c) **Regulations; good engineering practice—** Not later than six months after August 7, 1977, the [Administrator](/usc/42/7602.md?p=a), shall after notice and opportunity for public hearing, promulgate regulations to carry out this section. For purposes of this section, good engineering practice means, with respect to stack heights, the height necessary to insure that emissions from the stack do not result in excessive concentrations of any [air pollutant](/usc/42/7602.md?p=g) in the immediate vicinity of the source as a result of atmospheric downwash, eddies and wakes which may be created by the source itself, nearby structures or nearby terrain obstacles (as determined by the [Administrator](/usc/42/7602.md?p=a)). For purposes of this section such height shall not exceed two and a half times the height of such source unless the [owner](/usc/42/13641.md?p=4) or operator of the source demonstrates, after notice and opportunity for public hearing, to the satisfaction of the [Administrator](/usc/42/7602.md?p=a), that a greater height is necessary as provided under the preceding sentence. In no event may the [Administrator](/usc/42/7602.md?p=a) prohibit any increase in any stack height or restrict in any manner the stack height of any source.

## Source credit

(July 14, 1955, ch. 360, title I, § 123, as added Pub. L. 95–95, title I, § 121, Aug. 7, 1977, 91 Stat. 721.)

## Notes

### Statutory Notes and Related Subsidiaries

### Effective Date

Section effective Aug. 7, 1977, except as otherwise expressly provided, see section 406(d) of Pub. L. 95–95, set out as an Effective Date of 1977 Amendment note under section 7401 of this title.