Help with Easy Duct Calculator

History. The History tab (the clock icon) beside Results opens your last 20 calculations as a table: air flow, duct size, head loss and velocity, with the aspect ratio and the spare capacity of each duct. They stay on your device, follow your Settings (change the roughness or the safety factor and every row is sized again), and Clear history deletes them. Set a flow to 0 to remove that row.

Change a row in place. Tap a number in a row to change it there. Give a new height and the width is worked out again within the same head loss and velocity limits the row was sized with. Tap Head loss or Velocity to change that limit, or type one where it shows N/A to size with it too. A change of size alone updates the row instead of adding a new one.

Add to flow. Each amount you add gets its own row, sized on its own, under the new total; a line at the side ties the total, the amount and the flow it was added to. Change the flow or an amount and the totals above it are worked out again and light up briefly. Type over a total and it stands on its own: the line to the rows under it is cut.

Either side of a rectangle. In a History row you can type the width or the height; the other side is worked out. The side you typed is shown in black, the one worked out in teal.

Show or hide the amounts. The button beside the tabs hides the Add to flow rows; each total then shows the amount added under its flow.

Results and History tabs. Swipe left or right to switch between them. Tap the open tab again to fold the card away, and once more to open it.

Tablets on their side and desktops. History fills the left column and the inputs with the results sit on the right. The gear opens Settings in History's place.

Sizing. When the app picks the height of a rectangle, it now aims for a square duct (1:1) when the equivalent diameter needed is under 10 in (254 mm), and 3:1 above that. A duct added to a rectangular main is kept at least 2 in (50 mm) lower than the main. Round ducts larger than the largest standard size now go up to the size step, so the velocity limit always holds.

Wide screens. When there is room, the limits and the results get columns of their own, and a button beside each size switches that row between a rectangular and a round duct.

Adding to the flow. While the Add to flow box under Air flow is open, the box you are typing in is white and the other one grey. After you add a number, the flow box shows the sum it just made in small figures beside the new flow, such as 1700 + 300 =, so you can check it at a glance. It works the same in Cross-Check.

Results. Head loss now comes straight after the flow, above velocity, in both the normal results and Cross-Check. On narrow screens long labels switch to a shorter form (for example Equiv. diameter) instead of being cut off.

Tablets. On an iPad or Android tablet held sideways, Settings now opens in the space under the two cards and scrolls on its own when it does not fit, instead of hiding behind the gear.

Equivalent duct. The results now have their own Calculated Results card, as on the main screen, and show the equivalent diameter of both ducts: the existing one sits under it, the new one is in the results. On a wide screen the converter takes the left side and your duct sizing or Cross-Check stays on the right, so both can be used side by side.

Starting size. When the app suggests a rectangular size from the flow, W is now the short side (for example 12 × 36 rather than 36 × 12).

Clearer results. In Cross-Check the A and B values line up in one column. The Display size list only offers sizes that make a difference on your screen. The mm.WC/100m head-loss unit has been removed; Pa/m and in.WC/100ft remain.

iPhone and iPad. On iPhone the app stays upright. Results and Settings now scroll all the way to the end, and the last card runs to the bottom edge of the screen.

Windows. The window opens without a blue flash, the header no longer slides under the title bar, the bottom of each card is no longer cut off, and lists spring back gently at their ends.

About. A Copy button next to the email address, for computers where email links do not open a mail app.

Two methods changed to follow ASHRAE more closely.

Velocity. In a rectangular duct, velocity is now the flow divided by the real width × height. Earlier versions divided by the area of the equivalent round duct, which is smaller. The velocity shown is now lower — about 6% for a square duct and more for flat ones — so a velocity limit gives a slightly smaller duct. Round ducts are unchanged.

Friction. The friction factor now comes from the Colebrook equation instead of Altshul–Tsal. For galvanised steel the head loss moves by less than 2%. Rough ducts such as fibreglass or concrete now show a higher, more accurate head loss, especially in small sizes.

Pressure loss uses the Darcy–Weisbach equation. The friction factor comes from the Colebrook equation by default; Haaland or Altshul–Tsal can be chosen in Settings. Air density and viscosity come from the temperature and altitude set in Settings.

Colebrook and Haaland agree within about 1.5%. Altshul–Tsal matches them for smooth ducts but gives a lower head loss for rough ones, by about 7% for 4 in fibreglass and 20% for 4 in concrete.

A rectangular duct uses its Huebscher equivalent diameter for friction, and its velocity is the flow over the actual duct area, as in ASHRAE. Since 1.14 the hydraulic diameter can be chosen instead in Settings (Rectangular duct diameter); friction then runs on Dh and the actual velocity, and is about 1 to 2.5% lower for the same duct, more for flat ones. Losses cover straight duct only — add elbows, takeoffs and dampers separately.

Yes. All calculations run on your device, so you can size ducts on site with no signal.

Turn on Buildable size step in Settings and pick a step, such as ½, 1 or 2 in, or 25, 50 or 100 mm. Rectangular sides are rounded up to that step.

In millimetres a fraction under 1 mm is dropped first, as long as the duct still meets your limits as shown, so 200.1 mm stays 200 mm rather than going to the next step.

With Apply to round duct on, round ducts use the same step. With it off, they go to the next standard spiral duct size.

It is the flow safety factor from Settings. When it is not zero, the duct is sized for the flow plus that percentage, and the results show this as Design flow.

Use the IP / SI switch at the top to change every unit at once, or tap the unit chip next to any value to change just that one. You can mix units, for example L/s for flow and Pa/m for head loss.

It sizes one duct against two scenarios at the same time and uses whichever needs the larger duct, so you can see whether a single size still works when the flow or the limits change.

Tap the button with two crossed rectangles at the top. Enter the existing duct, then type either side of the equivalent duct; the other side is worked out and rounded up to the step in Settings, and the exact size is shown in the results. The small button beside each duct switches it between rectangular and round. The equivalent diameter of the existing duct is shown under it, and that of the new duct in the results.

With Friction the two ducts carry the same flow with the same friction loss, but a squarer or round duct runs faster. With Velocity they have the same cross-section, so the velocity stays the same, but a flatter duct has more friction. The results show both changes; a change for the worse is shown in amber.

Yes. Persian and Arabic digits are converted to Latin digits automatically as you type.

Yes. Email a short description of what you need and how you'd use it on a project.