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Guide C Reference data (2007)
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Guide C Reference data (2007)

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Guide C provides the fundamental data required for building services design. it is an essential instrument for those involved in the building professions.

The Guide is made up of 6 sections:

1. Properties of Humid Air

2. Properties of Water and Steam

3. Heat Transfer

4. Flow of Fluids in Pipes and Ducts

5. Fuels and Combustion

6. Units, Standards and Mathematical Data.

CIBSE Guide C was comprehensively updated for the previous edition in 2001 edition. Although basic physical data do not change with time, the refinement of measurement and calculation techniques and further research make regular review essential. Many of the changes to this edition are therefore small incremental changes, reflecting such refinement. It was however recognised that section 4, Flow of fluids in pipes and ducts, while heavily revised for the 2001 edition, was at that time unable to take account of the latest European research. The report of this research has now been obtained and its results distilled into this edition of Guide C.

The opportunity has also been taken to rewrite and clarify the text and to delete many pages of tabular data providing pre-calculated pressure drops through pipes. It was felt that these tables have outlived their usefulness now that accurate pressure drops can easily be calculated using spreadsheets or computer programs. Such a spreadsheet is provided on the CD-ROM that accompanies this Guide (as hard copy) or can downloaded as part of the Supplementary files as described below.


Supplementary files

Note: Guide C is supported by a number of supplementary files that are freely available to CIBSE members here. The downloaded zipped folder contains PIPE SIZING and DUCT SIZING SPREADSHEETS previously available on the CD accompanying the hard copy Guide. It also contains the C4 instructions file - a guidance note, updated in Dec 2018, that provides instruction on the use of the spreadsheets. These files will be e-mailed to purchasers of pdfs. Note: to correctly generate tables, users need to select the material, temperature and glycol or units (as appropriate) before other options are made available via the drop-downs (such as diameter).


In addition, a number of corrections have been made to-date (issued Oct 2007, May 2012, Feb 2014 and March, May and July 2016). This can be freely accessed and downloaded as a single list from here. Details of these are:

Oct 2007 - Corrections to 4-58 & 4-63

May 2012 - Correction to 3-25

Feb 2014 - Corrections to 4-22 & 4-25

Mar 2016 - Correction to 3-29 

May 2016 - Corrections to 3-21, 3-35 & 4-64

Jul 2016 - Corrections to 5-4 

The pdf download of the Guide itself from the link above includes the Corrigenda sheet following the front cover.

ADDITIONAL INFORMATION: Tables relating to natural gas (extracted from the old 2001 edition of Guide C)

A number of members have requested tables previously included in Guide C: 2001 but which were omitted from the 2007 edition. These tables assumed incompressible flow but "the method may be used with reasonable accuracy so long as the drop in pressure along the pipe does not exceed 10 percent of the initial (absolute) inlet pressure” as stated in the old edition. The 2007 revised guidance states that pressure drops are "best obtained by direct calculation using the method explained in section 4.3."

However, we do make available here the relevant section from the 2001 edition containing these tables expressly covering the flow of natural gas in pipes (Tables 4.45 and 4.46) for your reference purposes. Again, do note that their use does not accord with current CIBSE guidance


Authors: W P Jones (consultant); D L Loveday (Loughborough University); A H Taki (De Montford University); P Koch (Université Joseph Fourier, Grenoble; Coventry University); M R I Purvis (Chairman) (University of Portsmouth); P D Compton (Colt International Ltd.)

Steering Committee:

Chair: W P Jones (consultant)

Members & contributors: J F Armour; B G Lawrence; H B Awbi (University of Reading); P D Compton (Colt International Ltd.); R M Harris (Centre for Window and Cladding Technology); M J Holmes (Ove Arup & Partners International Ltd.); B P Holownia (Loughborough University); J Moss (Ove Arup & Partners International Ltd.); T Muneer (Napier University); H K Versteeg (Loughborough University); F Sprenger (Coventry University); R Dando (Coal Research Establishment); M Drew (BP Amoco plc); R J Harris (Advantica Technologies Ltd.); K Mildren (University of Portsmouth)


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