Last edited 20 Feb 2025

Equivalent area

Domestic Ventilation Compliance Guide, 2010 Edition (with 2011 amendments), published by the Department for Communities and Local Government in July 2011, suggests that equivalent area is: ‘…a measure of the aerodynamic performance of a ventilator. It is the area of a sharp-edged circular orifice which air would pass through at the same volume flow rate, under an identical applied pressure difference, as the opening under consideration.’

Approved Document O: Overheating, published by HM Government in 2021, defines equivalent area as: ‘A measure of the aerodynamic performance of an opening. It is the area of a sharp-edged circular orifice through which air would pass at the same volume flow rate, under an identical applied pressure difference, as through the opening under consideration.’

The equivalent area of a background ventilator is determined at 1Pa pressure difference in accordance with Table 1.7 of Approved document F: Volume 1: Dwellings, 2021 edition.

See also: Effective area and Discharge coefficients, free, effective and equivalent areas

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Discharge coefficients, free, effective and equivalent areas

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