Ductulator - HVAC Duct Sizing

Review by eFreeware

Ductulator takes the duct sizing charts handed out by HVAC manufacturers and turns them into something you carry on your phone. Instead of running a finger down a printed table to find a size that fits, you enter the numbers you already know and let the app work through the combinations. That is the core idea, and it is a narrow one: this is a calculator for ductwork, not a general engineering toolbox.

The developer says the design grew out of surveying engineers about what they needed, and the two modes reflect that. One is for choosing a duct size when you are laying out a system; the other is for checking dimensions and airflow in something already built. If your work involves sizing supply or return runs, or working out what an existing installation is doing, this is built for you.

It costs $2.99, carries no ads and has no in-app purchases, so the whole tool arrives in one transaction. Over 5,000 installs and a 4.4 average from 350 ratings suggest a small but settled audience rather than a mass-market hit. For a specialist calculator, that seems about right.

Getting a range of sizes instead of a single answer

Design Mode is the part the developer leads with. You give it either a maximum friction rate or a maximum velocity, and it returns a list of duct sizes that satisfy that limit. The list covers both rectangular and circular ducts, so you are not locked into one shape before you have seen the options.

What appeals to me here is the range rather than a single number. A chart usually pushes you toward one nominal size, and you take it or leave it. Seeing several candidates side by side, each with its resulting friction rate and velocity, gives you room to pick something that fits the space you actually have, or that matches a size already stocked on the job.

The figures assume clean galvanized steel duct and standard air, at 0.075 lb/ft3 (1.2 kg/m3). Those are the usual assumptions behind published duct sizing data, but they are assumptions all the same. If your system runs at a different air density or uses lined or flexible duct, the figures the app returns describe the reference case.

Sizing Mode for checking what is already installed

The second mode works in the opposite direction. Enter the airflow and duct size, and the friction rate and velocity follow. The developer describes this as the way a traditional ductulator is used, and it was added after users asked for it.

This is the mode I would expect to reach for when surveying a building. You measure what is there, enter the dimensions, and see what the numbers say about the air moving through it. Adjusting one value at a time and watching the results shift is a quick way to understand how sensitive a run is to a change in size or flow.

Both modes sit behind the same unit setting. You can work in imperial or SI measurements, and switching between them is a single change rather than something you redo for every calculation. For anyone who works across projects in different regions, or who receives drawings in units they do not normally use, that saves a step.

What it asks of you before you start

This is a paid app at $2.99, with no advertising and nothing sold inside it. You pay once and the tool is yours, which is a straightforward arrangement for something you might open on a site visit or in the office.

The requirement that matters more is knowledge, not money. To use Design Mode you need to know which limit applies to your project, a friction rate or a velocity, and what value is appropriate. The app does not decide that for you. Sizing Mode asks for dimensions and airflow that you have to obtain yourself.

It also assumes the standard conditions noted above. Clean galvanized steel at standard air density is the reference, and the results should be read in that light. None of this is unusual for a duct calculator, but it does mean the app is a fast way to do a familiar calculation, not a substitute for knowing which calculation you need.

Fitting it into a working day

The most natural use is replacing the printed charts and slide-style ductulators that manufacturers supply. Those are fine at a desk, but they are awkward to carry and easy to misread when you are standing in a mechanical room. A phone calculator removes that friction, and the developer pitches this as a faster, more versatile equivalent of those charts.

I would treat the two modes as answering different questions. Use Design Mode early, when the layout is still open and you want to compare rectangular against circular options under a chosen limit. Use Sizing Mode later, on an existing system, when the question is what the current ductwork is doing rather than what it ought to be.

The developer invites feedback and says it will shape future updates, and the presence of Sizing Mode suggests that has already happened once. The app was released in 2022 and last updated in 2026, so it has been kept current. For a small utility like this, that continuity is a reasonable sign.

One habit worth forming is to note which limit you used and what assumptions you applied, so the output means something when you come back to it. The app gives you numbers quickly; recording the basis for them is still your job, and on a project that runs for months that note is often as valuable as the calculation itself.

A focused tool for people who size ducts

Ductulator does one job and does it without clutter. Two modes, a unit switch, and results that update as you change inputs. If duct sizing is part of your work, the $2.99 outlay is small against the time saved looking up charts, and the absence of ads and purchases keeps the experience clean.

The 4.4 average from 350 ratings points to an audience that mostly gets what it expected, which fits a paid specialist tool. It is not trying to teach you HVAC design, and it will not tell you which friction rate or velocity to target. It assumes you already know, and it speeds up the arithmetic from there.

Design engineers and technicians who regularly size ducts or survey existing systems are the people who will get the most from it. If you are learning the subject, the app will happily produce numbers, but the judgment about whether they are the right numbers stays with you.