Terms of Use
Last updated: October 10, 2026
These terms apply to your use of https://ductchart.com (the "site"), operated by Duct Chart. By using the site you agree to them.
Disclaimer: estimates only
The calculators, charts and printouts give estimates only. Installers must follow the design documents, the manufacturer’s data and local code, and must not size or install ductwork from this site alone.
https://ductchart.com is a calculation aid for trained HVAC professionals. Results are estimates based on published friction-chart methods (Colebrook and Darcy-Weisbach, with a roughness of 0.0005 ft for galvanized duct) and may differ from your duct-sizing chart, ductulator or the equipment manufacturer’s data by 5% or more. Flexible duct results may differ by a factor of two or more depending on stretch, compression, sag and manufacturer.
This site does not replace an ACCA Manual J, S or D calculation, the equipment manufacturer’s blower and expanded performance tables, or an engineer’s design. The CFM per ton figures are starting estimates, not design airflow.
You are responsible for checking every size against the applicable code (IMC, IRC and local amendments), the manufacturer’s installation instructions and the measured static pressure and airflow of the system before you install anything. The site is not professional, engineering or safety advice. Real systems vary with fittings, joints, installation, altitude and temperature.
Flex duct: friction depends strongly on installation. Install flex fully stretched (4% compression or less), supported and without sag. Compressed or sagging flex can be several times higher friction than shown.
Use of the site
You may use the site and print the charts for personal and commercial purposes, free of charge. Do not misuse the site, attempt to disrupt it, or copy the site itself for redistribution.
No warranty
The site is provided "as is" without warranties of any kind, including accuracy or fitness for a particular purpose. To the extent permitted by law, Duct Chart is not liable for any loss or damage arising from use of the site, the charts or the calculators. Nothing in these terms excludes rights that cannot be excluded under applicable law, including the Australian Consumer Law.
Third-party links
The site may link to other websites, including advertisers and affiliate partners. We are not responsible for their content or practices.
Changes
We may update these terms. Continued use of the site means you accept the updated terms.
Governing law
These terms are governed by the laws of New South Wales, Australia, and you submit to the non-exclusive jurisdiction of its courts.