Effective August 18, 2026 · Last updated August 18, 2026
This is an estimating tool, not certified engineering software. Every number it gives you is your responsibility to check. It is not approved for permit submissions. If something it calculates turns out wrong and you build from it, the most you can recover is what you paid for the subscription. Cancel any time; we'll refund a charge you're unhappy with.
That summary is here so you actually know what you agreed to. The full terms below are what legally govern, and if the two ever conflict, the full terms win.
The DuctDuck website and application (the “Service”) are provided by DuctDuck Software LLC, an Ohio limited liability company, located in Ohio, United States (“we”, “us”, “our”). You can reach us at [email protected].
By creating an account, starting a trial, or using the Service, you agree to these Terms of Service. If you don't agree, don't use the Service.
The Service performs HVAC-related estimating calculations, including residential heating and cooling load estimates, equipment capacity suggestions, airflow (CFM) figures, duct friction rates, duct sizes and register and grille selections.
The Service is a field estimating aid. It is not approved, certified or verified by the Air Conditioning Contractors of America (ACCA) or any other standards body, and it is not a substitute for a full ACCA Manual J, Manual S, Manual D or Manual T calculation performed with approved software or by a qualified professional.
Output from the Service does not constitute engineering advice, professional design services, or a certified load or duct calculation, and must not be submitted as such to any permitting authority, code official, inspector, builder or client.
The calculations are simplified. In particular, the “Quick” load mode is an explicit rule-of-thumb approximation, and the “Detailed” mode is a simplified component calculation that does not model every correction factor, duct loss, latent load split or edge case addressed by full Manual J8. Results may differ materially from a certified calculation.
By using the Service you represent and agree that:
You can sign in with a Google account or with a one-time code sent to your email address. Both methods resolve to the same account when they use the same email address.
You are responsible for keeping access to your email account and Google account secure, and for activity that happens under your account. Tell us promptly at [email protected] if you believe someone else has gained access.
One subscription is for one person. Sharing an account with other technicians, or across a crew, is not permitted — if you need multiple users, contact us.
New subscribers get a 14-day free trial. A valid payment method is required to start it. If you don't cancel before the trial ends, the subscription automatically converts to a paid subscription and your payment method is charged.
Current pricing is $14.99 per month or $119.00 per year in U.S. dollars. Subscriptions renew automatically at the end of each billing period until cancelled. Prices shown at the time you subscribe apply for that billing period.
Payments are processed by Stripe, Inc. We never receive or store your full card details. Your use of Stripe's checkout is also subject to Stripe's own terms and privacy policy.
You can cancel at any time from the billing page inside the app, which opens Stripe's customer portal. Cancellation takes effect at the end of the current billing period — you keep access until then, and you are not charged again.
If a renewal payment fails, we do not lock you out immediately. Access continues while the payment is retried. If it ultimately fails, the subscription is cancelled and access to paid features ends, but you retain read and export access to your saved data as described in section 6.
Prices are exclusive of applicable sales tax, which may be added at checkout depending on your location. The Service is currently offered only in the United States, Canada and certain other territories, and is not available to customers in the European Union or United Kingdom.
See our Refund Policy, which forms part of these terms.
The job data you create — project names, rooms, dimensions, loads and duct designs — belongs to you. We claim no ownership of it.
You can export your data at any time from within the app. If your subscription ends, you keep read and export access to work you already saved; you simply can't save new work to the cloud. We think locking you out of your own records would be an unreasonable thing to do.
How we handle personal information is described in our Privacy Policy.
You can ask us to delete your account and data at any time by emailing [email protected].
Don't:
Found a security problem? Please email [email protected] rather than publishing it. Good-faith reports are welcome and we won't come after you for making one.
The Service, including its code, design, text, calculation implementations, logo and name, is ours and is protected by copyright and trademark law. Your subscription grants you a limited, non-exclusive, non-transferable, revocable licence to use the Service for its intended purpose. It does not transfer ownership of anything.
The underlying engineering equations and methods are, of course, published industry standards and belong to nobody. Our particular implementation of them does not.
ACCA, Manual J, Manual S, Manual D, Manual T, ASHRAE and any other third-party marks referenced are the property of their respective owners. Their use here is descriptive and does not imply endorsement, affiliation or approval.
THE SERVICE IS PROVIDED “AS IS” AND “AS AVAILABLE”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED. TO THE MAXIMUM EXTENT PERMITTED BY LAW, WE DISCLAIM ALL WARRANTIES INCLUDING ANY IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, NON-INFRINGEMENT, AND ANY WARRANTY ARISING FROM COURSE OF DEALING OR USAGE OF TRADE.
WITHOUT LIMITING THE ABOVE, WE DO NOT WARRANT THAT THE SERVICE'S CALCULATIONS ARE ACCURATE, COMPLETE, CURRENT, ERROR-FREE, SUITABLE FOR ANY PARTICULAR PROJECT, OR COMPLIANT WITH ANY CODE, STANDARD OR REGULATION; THAT THE SERVICE WILL BE UNINTERRUPTED OR AVAILABLE AT ANY PARTICULAR TIME; OR THAT DATA WILL NOT BE LOST. YOU ARE RESPONSIBLE FOR MAINTAINING YOUR OWN BACKUPS OF IMPORTANT WORK, WHICH THE EXPORT FEATURE EXISTS TO LET YOU DO.
Some jurisdictions do not allow the exclusion of certain warranties, so parts of this section may not apply to you.
TO THE MAXIMUM EXTENT PERMITTED BY LAW, WE WILL NOT BE LIABLE FOR ANY INDIRECT, INCIDENTAL, SPECIAL, CONSEQUENTIAL, EXEMPLARY OR PUNITIVE DAMAGES, OR FOR ANY LOSS OF PROFITS, REVENUE, DATA, GOODWILL, BUSINESS OPPORTUNITY, OR FOR THE COST OF SUBSTITUTE GOODS OR SERVICES, ARISING OUT OF OR RELATING TO YOUR USE OF THE SERVICE, WHETHER BASED IN CONTRACT, TORT (INCLUDING NEGLIGENCE), STRICT LIABILITY OR ANY OTHER THEORY, AND WHETHER OR NOT WE WERE ADVISED OF THE POSSIBILITY.
THIS EXPRESSLY INCLUDES, WITHOUT LIMITATION, ANY DAMAGES ARISING FROM: EQUIPMENT SELECTED OR DUCTWORK DESIGNED, FABRICATED OR INSTALLED IN RELIANCE ON THE SERVICE; SYSTEM PERFORMANCE, COMFORT, HUMIDITY, NOISE OR EFFICIENCY OUTCOMES; REWORK, CALLBACKS, WARRANTY CLAIMS OR REMEDIAL WORK; FAILED INSPECTIONS OR REJECTED PERMIT SUBMISSIONS; PROPERTY DAMAGE; OR ANY CLAIM MADE AGAINST YOU BY A THIRD PARTY.
OUR TOTAL AGGREGATE LIABILITY FOR ALL CLAIMS RELATING TO THE SERVICE IS LIMITED TO THE GREATER OF (A) THE TOTAL AMOUNT YOU ACTUALLY PAID US IN THE TWELVE MONTHS IMMEDIATELY PRECEDING THE EVENT GIVING RISE TO THE CLAIM, OR (B) ONE HUNDRED U.S. DOLLARS ($100).
These limits apply even if a remedy fails of its essential purpose. They do not apply to liability that cannot be limited or excluded by law, such as liability for fraud, fraudulent misrepresentation, death or personal injury caused by negligence, or gross negligence or wilful misconduct where applicable law prohibits its exclusion.
You acknowledge that the subscription price reflects this allocation of risk, and that we would not be able to offer the Service at this price without it.
You agree to indemnify and hold us harmless from any claim, demand, loss, liability, damage, cost or expense (including reasonable legal fees) arising from: your use of the Service; your breach of these terms; your presentation of Service output as a certified or code-compliant calculation; or any HVAC design, specification or installation you carry out or recommend, whether or not it relied on the Service.
You can stop using the Service and cancel at any time.
We may suspend or terminate your access if you materially breach these terms, if your use threatens the security or availability of the Service, if required by law, or if we discontinue the Service. Where practical and lawful we'll give you notice and a chance to fix the problem first.
If we discontinue the Service entirely, we will give at least 30 days' notice by email, refund the unused portion of any prepaid period, and keep export working through that notice period so you can retrieve your data.
Sections 6, 8, 9, 10, 11, 14 and 15 survive termination.
We may change the Service, including adding, modifying or removing features.
We may update these terms. For material changes we will give notice by email or in the app at least 14 days before they take effect. Continuing to use the Service after that means you accept the updated terms. If you don't accept them, cancel before they take effect and we will refund the unused portion of your current period.
Price changes will never apply to a billing period you have already paid for, and we will give at least 30 days' notice before a price change affects your renewal.
These terms are governed by the laws of the State of Ohio, United States, without regard to its conflict-of-laws rules. The state and federal courts located in Mahoning County, Ohio have exclusive jurisdiction over any dispute, and you and we consent to venue there.
Before filing anything, please email [email protected] and give us 30 days to try to resolve it. Most problems are a misunderstanding or a bug.
Any claim must be brought within one year of when it arose, to the extent permitted by law.
Questions about any of this? Email [email protected]. If a clause seems unreasonable, say so — these terms exist to set expectations fairly, not to hide anything.