Duct Size Calculator – Terms of Service

Agreement to these terms

By downloading, installing, or using Duct Size Calculator ("the App"), you agree to these Terms of Service. If you do not agree, do not use the App.

Duct sizing estimates

The App estimates round and rectangular duct sizes, equivalent diameters, and friction rates using standard published equal-friction sizing methods (commonly referenced SMACNA/ASHRAE residential and light-commercial duct sizing guidance) and the Altshul-Tsal approximation of the Colebrook-White friction equation. It also provides general reference information (typical airflow ranges, typical target velocities) drawn from the same class of published references.

Not professional engineering advice

The App is a field-reference and estimation tool. It is not a substitute for a full engineering calculation, a licensed HVAC professional's judgment, or compliance verification against applicable building and mechanical codes.

Specifically:

• The App does not perform a full Manual D (or equivalent) system design calculation. It does not account for fitting losses (elbows, transitions, dampers, grilles), equipment static pressure ratings, duct leakage, or load calculations (Manual J or equivalent).
• Results are estimates based on the inputs you provide. The App cannot verify that those inputs (airflow, target velocity, duct material, run length) are correct for your specific installation.
• Duct sizing, HVAC system design, and mechanical installations are subject to local building codes, mechanical codes, and jurisdictional requirements that vary by location and are not evaluated by the App.
• You are solely responsible for verifying all results against manufacturer specifications, applicable codes, and — for any code-required, safety-critical, or commercial installation — a licensed HVAC engineer or qualified professional.

By using the App, you agree not to rely on it as the sole basis for a final, code-required, or safety-critical HVAC design or installation decision.

Provided "as is"

The App is provided "as is" and "as available," without warranty of any kind, express or implied, including but not limited to warranties of merchantability, fitness for a particular purpose, accuracy, or non-infringement. We do not warrant that calculation results will be error-free or suitable for any particular installation.

Limits on our liability

To the maximum extent permitted by applicable law, in no event shall Foster Apps LLC or its owners, employees, or affiliates be liable for any indirect, incidental, special, consequential, or punitive damages, or any loss of profits, data, or goodwill, arising from or related to your use of the App — including but not limited to damages arising from an incorrect, incomplete, or misapplied duct sizing result, even if advised of the possibility of such damages.

To the maximum extent permitted by applicable law, our total liability for any claim arising from your use of the App shall not exceed the greater of (a) the amount you paid for the App or any subscription in the 12 months preceding the claim, or (b) $50 USD.

Some jurisdictions do not allow the exclusion or limitation of certain damages, so some of the above limitations may not apply to you.

Billing and cancellation

Subscription terms, pricing, free trial details, and cancellation are governed by Apple's App Store terms and displayed at the point of purchase. Manage or cancel your subscription through your Apple ID account settings.

Changes to these terms

We may update these Terms from time to time. Continued use of the App after changes take effect constitutes acceptance of the revised Terms. When these Terms change, the "Last updated" date at the top of this page will be revised.

Questions

If you have any questions about these Terms, please contact us at support@fosterapps.com.