DuctCalc questions and answers

Yes. Size a duct takes an airflow plus a friction rate or a target velocity and returns the round diameter. Check a duct takes an airflow plus a duct you already have, round or rectangular, and returns the velocity and the friction rate it runs at.

It rounds the exact diameter up to a catalogue size: 3 to 40 in in imperial, and the EN 1506 spiral steps from 80 to 1,250 mm in metric. It cannot know what your particular shop has on the shelf, so it shows the exact size next to the stock one.

Three: galvanized steel, duct board and flex duct. There is no spiral choice, although the metric stock sizes follow spiral catalogues. Each has its own roughness, so the friction rate and the sized diameter change with the material.

With the equivalent-diameter formula from the back of many wheels, De = 1.30 x (a x b)^0.625 / (a + b)^0.25. The app steps the height in even inches (50 mm in metric) and rounds each width up. Pairs above 4:1 get a chip and pairs above 8:1 are dropped.

The real one, airflow divided by width times height. The friction rate is worked out through the equivalent round diameter at the same airflow. Mixing those two up is the classic hand-calculation error.

The badge compares the velocity with a band for the application you choose, such as Residential · supply-air branch. It can say Above recommended band · check noise. It does not measure or predict noise, and there is no bedroom setting.

No. The six bands are fixed. You can pick which one the badge uses, either under the badge or in Settings > Check velocity against.

Yes. In Settings > Units choose Metric, then L/s or m³/h as the airflow unit. Lengths are in mm, velocity in m/s and friction in Pa/m. The numbers you already typed convert when you switch.

Standard air at 20 °C at sea level. There is no altitude or temperature setting, so a mountain job or a hot attic is not corrected.

It solves the same Darcy-Weisbach and Colebrook model the friction chart comes from, rather than reading a curve fit. In its own checks it stays within half an inch of hand-read wheel values, and a printed power-law fit can read about a tenth of an inch away. Expect close, not identical.

Not in one step. Use Check a duct, enter the diameter, and change the airflow until the friction rate shows your target. A 6 in galvanized duct reaches 0.1 in.wg/100ft at about 111 CFM.

Each calculation with its inputs and material, saved on its own a few seconds after you stop editing. Tap a row to reload it, swipe it right to name the duct run, or swipe to delete. Free keeps the last ten.

Two things. History keeps every calculation instead of the last ten, and Share duct schedule sends the whole history as one plain-text list through the share sheet, grouped by day with your run names. It is one purchase, not a subscription, and the sizing itself stays free.

Yes, one calculation at a time. Copy result puts the answer, inputs and material on the clipboard as text.

No ads, no account, no sign-up. The network is only used by the App Store for buying or restoring Pro.

It runs on iPhone and iPad. There is no Android, Mac or Apple Watch app, and no widget.

No. The shared duct schedule is plain text. A single result can be copied as text.

No. DuctCalc covers friction in straight duct and velocity. Fittings, equivalent lengths, coils, filters, fans and the load calculation are outside it.

On the device. There is no cloud sync, so a phone you set up as new starts with an empty history.