HVAC duct calculator

English · Українська

A web calculator for sheet-metal ductwork. You list the duct fittings of a ventilation system (straight ducts, elbows, reducers, tees, crosses, caps, branch-in collars) with their sizes, and it returns the sheet-metal area of every item, the metal thickness by the Ukrainian norm, a metal list grouped by thickness with the number of sheets to order, the insulation area and a cost estimate from your own prices.

Live: https://hvac-duct-calculator-rho.vercel.app

The interface is in Ukrainian by default, with an English version: the УКР / EN switch at the top right changes the language, and the browser remembers the choice. The tool is built for duct designers and sheet-metal shops in Ukraine. Everything is calculated in the browser; there is no backend and nothing is stored apart from the language choice.

What it does

• Metal area per item. Developed surface of each fitting from its geometry, with the connection allowance for flanges and the cutting coefficient for elbows.
• Metal thickness. Looked up from the table of ДБН В.2.5-67:2013, annex Ц (round: by diameter, rectangular: by the larger side). The engineer's own table is available as an option.
• Metal list by thickness. Area per thickness, area to order with a margin (20 % by default) and the number of sheets for the chosen sheet size (1000 × 2000, 1250 × 2500 or 1500 × 3000).
• Insulation area (beta). Pick an insulation material per item (six from the engineer's spreadsheet); the outer surface of the layer is the metal geometry with each size increased by twice the layer thickness. Area per item, a list per material and a total. The model will be refined with the engineer.
• Cost estimate. Enter your own price per m² (UAH) for each sheet thickness and insulation material: cost per line and in total. Metal is priced on the area to order. No prices are preset.
• Input warnings. Unusual but valid input (aspect ratio of 3 and above, over 6.3, a side over 2000 mm, a large elbow radius) is flagged and never changed.
• Sketches. Each fitting card shows a thumbnail of its isometric sketch; a click opens the full sketch with the dimension letters used in the form.

Fittings folded into tiles, with the results table	Totals, metal and insulation lists with prices

On a phone the side panel becomes a column of round buttons at the screen edge, with a quick menu of common kinds and a searchable list of all of them.

Supported fittings

19 kinds, named by the designations a Ukrainian spec uses.

In the English interface the same kinds have short English codes (C = circular, R = rectangular): CD, RD ducts; CE, RE elbows; CR, RR, RC reducers; CTap, RTap collars; CT, CRT, RT, RCT tees; CX, CRX, RX, RCX crosses.

Group	Kinds
Straight ducts	round (КПв), rectangular (ППв)
Elbows	round (КВд), rectangular (ПВд), any angle
Reducers	round (КП), rectangular (ПП), rectangular to round (ППК)
Caps	round, rectangular
Branch-in collars	round (Квр), rectangular (Пвр)
Tees	round (КТ), round with a rectangular branch (КПТ), rectangular (ПТ), rectangular with a round branch (ПКТ)
Crosses	round with round branches (ККХ), round with rectangular branches (КПХ), rectangular with rectangular branches (ППХ), rectangular with round branches (ПКХ)

Tees and crosses subtract the branch openings from the main duct; thickness follows the main duct.

How the numbers are verified

The reference is a calculation spreadsheet that a practising HVAC engineer has used on real projects for years. The calculator was built against it, not just inspired by it:

• Fixtures are the source of truth. Expected values live in src/lib/calc/__fixtures__/ and are committed by hand, separately from the code. Each case is marked basis: 'geometry' (derived independently from first principles) or basis: 'excel' (follows the spreadsheet's convention). Tests are never adjusted to make code pass.
• The Excel is a reference, not the truth. Checking it line by line turned up formula bugs in the template. Where the spreadsheet is wrong, the calculator computes the correct value and the deviation is documented (ADR 0001, and known deviations).
• Open questions go to the engineer. Coefficients without a confirmed source are kept in config with a TODO(confirm) mark and listed in a register instead of being guessed. His answers are logged in docs/engineer-answers.md.
• Ukrainian norms. Thickness and the aspect-ratio limits come from ДБН В.2.5-67:2013.

Every engineering decision has its own record in docs/adr/ (context, decision, consequences, source), indexed in docs/decisions.md.

Architecture

src/lib/calc/        pure TypeScript core: geometry, thickness, waste factor, sheet count,
                     air properties and pressure drop. No framework, no validation library.
src/lib/validation/  Zod schemas around the core; errors are stable codes, not text
src/lib/form/        form layer: raw text -> validated input -> results; defaults and warnings
src/lib/i18n/        every user-visible string (Ukrainian and English dictionaries)
src/components/      React components; props only, no calculation

• Units: millimetres, degrees and m³/h at the boundary, SI inside the core, converted in one module.
• One developed length per fitting feeds every area figure, so two copies of the same geometry cannot drift apart.
• The core also computes pressure losses (Altshul friction, local resistances, air properties at given conditions). They are hidden in the UI for now and will come back as a separate aerodynamics mode.

Stack

Next.js (App Router), React, TypeScript (strict), Tailwind CSS, Zod, Vitest. Deployed on Vercel with Vercel Web Analytics. CI on GitHub Actions runs typecheck, lint and tests on every pull request.

Run locally

Requires Node 24 (see .nvmrc).

npm ci
npm run dev        # http://localhost:3000
npm test           # unit tests (Vitest)
npm run typecheck
npm run lint

Roadmap

• Adapters and plenum boxes
• Aerodynamics as a separate mode
• XLSX export of the specification