Feature spec
Goal: Send a clear invoice after finishing a job.
- Add a client, line items, a due date, and payment instructions.
- Preview the total before exporting a PDF.
- Keep an editable draft if export fails.
App Overview
Duct Calculator Elite
Duct Calculator Elite™ is an industry leading tool designed to simplify the job of duct sizing for HVAC professionals
$6.99 · In-app purchases
PRICE
$6.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 4.8
225 ratings · Top 5%
Evidence scope: No current overall US chart position is available. Category-chart positions shown in discovery are a separate scope. Revenue is a directional model estimate, not verified earnings.
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Build Kit
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A product spec, screen plans, and build steps for your coding agent.
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What's included17 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
Preview a sample Build Kit No email needed
Illustrative example: an invoice app for independent contractors. Your kit is tailored to the app you choose; this is not its generated content.
Screen plan
Invoice editor: Client at the top, editable line items in the middle, total and preview action at the bottom.
States: Empty draft, validation errors beside each field, exporting, and a retry action that preserves the draft.
Differentiate and validate
Hypothesis: Contractors need faster repeat invoices more than more templates.
First experiment: Test duplicating a previous job with five contractors. Watch where they hesitate before expanding the feature set.
The full kit adds a phased build plan, evidence notes, tool prompts, and implementation guidance. It is a plan for your coding agent, not a finished app.
Usage: Mechanics are fair game; never reuse the original name, branding, assets, or verbatim copy.
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Free quick prompt For a smaller starting point
Quick prompt
Good fit for mobile-first iOS and Android prototypes with managed app scaffolding.
// RORK SYSTEM PROMPT
Rork plan preview for Duct Calculator Elite: map the core Utilities workflow, choose the smallest differentiated feature set, define the data and monetization boundaries, then prototype the riskiest user journey first.
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Opportunities
AI-GENERATED OPPORTUNITY HYPOTHESES
These are generated suggestions, not verified review quotations. Check current App Store reviews and speak with users before treating a possible gap as a requirement.
Hypothesis 1
Introduce more input options and clear instructions.
Assumption to check: Limited input types and units may confuse users.
Validate with people who use this workflow before building.
Hypothesis 2
Add sharing options for better user engagement.
Assumption to check: No sharing capability for results directly from the app.
Validate with people who use this workflow before building.
Hypothesis 3
Allow users to save preferred units and settings.
Assumption to check: Lack of customization options for calculations.
Validate with people who use this workflow before building.
Hypothesis 4
Enhance history feature to include more details and edits.
Assumption to check: History does not provide detailed records.
Validate with people who use this workflow before building.
App evidence
Original App Store material. Ratings and screenshots describe the existing app, not proof of demand for your version.
App Store description
Duct Calculator Elite™ is an industry leading tool designed to simplify the job of duct sizing for HVAC professionals. This app allows users to calculate duct size, velocity, pressure drop, and flow rate for ductwork. Duct Calculator Elite™ features a highly intuitive interface which allows users to easily enter values with precision (without the use of cumbersome "slider" controls). In "Duct Size by Airflow" mode, the calculator allows users set airflow and either velocity or friction (Pressure Loss) and the calculator solves for round and rectangular duct dimensions. Aspect ratio of the rectangular duct can also be specified. In "Duct Size by Dimension" mode, users can enter either a round duct diameter or rectangular duct height and width. In addition, users can lock airflow, velocity, or friction and solve for the other variables. In "Pressure Drop" mode, users can convert between duct length, pressure drop, and friction values. This allows users to quickly determine exact pressure drop of a given installation or calculate the max duct length that can be used to maintain desired pressure drop. This feature compliments the two duct sizing calculators. Duct Calculator Elite™ provides users with a wide variety of preference setting including: -Duct Dimensional Units (Inches, Centimeters, or Millimeters) -Airflow Units (Cubic Feet per Minute, Cubic Feet per Second, Cubic Meters per Second, or Liters per Second) -Velocity Units (Feet per Second, Feet per Minute, or Meters per Second) -Pressure Loss Units (Inches of Water per 100ft or Pascals per Meter) -Duct Material (Aluminum, Concrete, Fibrous Glass Duct Liner, Flexible Duct-Metallic, Galvanized Steel, PVC Plastic Pipe, Smooth Liner, Spiral Steel, or Uncoated Carbon Steel) -Air Temperature (Fahrenheit, Celsius, or Kelvin) -Elevation (Feet or Meters) The Duct Calculator Elite™ solver uses friction loss equations contained in 2009 ASHRAE Handbook - Fundamentals. The next time you go to a meeting or out to the field, leave your Ductulator at home, you'll have everything you need right on your iPhone/iPad/iPod Touch! If you are not 100% satisfied with this calculator please email us at [email protected] so we can make things right before posting any negative reviews. We read all emails. We are also open to any suggestions you may have for future enhancements to this app.
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Screenshots
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Build scope
Plan a focused first version with your coding agent. These are planning assumptions, not a delivery guarantee.
Define the first version
Choose one audience and one core workflow. Use the kit to agree on its screens, data, and acceptance criteria before building.
Set boundaries
Decide which secondary features, integrations, and platform support can wait. Your version does not need to reproduce everything in the original.
Check the hard parts
Validate external services, specialist technology, data access, and ongoing costs for your chosen scope.
SUGGESTED BUILD STACK
React Native
Expo
React Navigation
React Native Paper
TypeScript
@react-native-clipboard/clipboard
BUILD KIT DIFFICULTY
Starter
From the Build Kit assessment.
A reliable timeline needs an agreed scope and a technical check. Ask your agent to estimate the phases in BUILD_PLAN.md after that review.
