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
HVAC Pipe Sizer - Gas Low
The "HVAC Pipe Sizer - Gas Low" application allows you to quickly size a simple low pressure (less than 1.5psi) gas piping system by inputting a number of piping and gas properties.
$4.99 · In-app purchases
PRICE
$4.99
In-app purchases
BUSINESS MODEL
Paid
No overall Grossing estimate available
RATING
★ 5.0
2 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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What's included16 files
A product spec, phased build plan, differentiation notes, and screen references.
- START_HERE
- AGENTS
- EVIDENCE
- SPEC
- BUILD_PLAN
- DIFFERENTIATION
- skills/
- screens/
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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 HVAC Pipe Sizer - Gas Low: map the core Productivity 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
Provide advanced settings for different gas types and conditions.
Assumption to check: Limited functionality for complex calculations
Validate with people who use this workflow before building.
Hypothesis 2
Enable users to share projects with others via email or social media.
Assumption to check: No project sharing features
Validate with people who use this workflow before building.
Hypothesis 3
Integrate visual representations of pipe sizes and layouts.
Assumption to check: Lack of visual aids or diagrams
Validate with people who use this workflow before building.
Hypothesis 4
Allow users to import/export data from spreadsheets or other tools.
Assumption to check: Inflexible input options
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
The "HVAC Pipe Sizer - Gas Low" application allows you to quickly size a simple low pressure (less than 1.5psi) gas piping system by inputting a number of piping and gas properties. You can specify the total gas flow in cuft/hr (CubicM/hr) and one of either pressure drop (in. wg or Pa), pipe internal diameter (inches) or gas velocity (ft/s) parameters. The results include both the exact and nominal pipe diameters and the calculated velocity and total pipe equivalent length. If you are analyzing an existing pipe system, there is an option to input the existing pipe internal diameter and one of either pressure drop or gas velocity parameters to derive the calculated gas flow and other remaining properties. You can specify additional parameters such as the type of gas, various properties of the gas, the pipe material type, the total length of pipe, quantities for up to 11 different types of pipe fittings, and much more. You can also choose to display values in either english or metric units. This application includes built-in pipe fitting equivalent length and nominal pipe sizing tables for a wide variety of pipe material types and diameters. The "HVAC Pipe Sizer - Gas Low" application uses slider controls that allow you to quickly increment or decrement the input values and immediately observe the calculated results. You can also manually input exact values. All values can be displayed in English (IP) and Metric (SI) units. This app now includes the HVAC Equipment Locator. Click here for details: http://bit.ly/1yTq539 This application was designed by Carmel Software Corporation, a leader in HVAC design software since 1995. In fact, Autodesk (the makers of AutoCAD) acquired our load calculation software and incorporated it into their leading 3D modeling software called Revit. We also offer the following additional applications for the iPhone/iPad: 1. HVAC Duct Sizer 2. HVAC Pipe Sizer – Gas Low Pressure 3. HVAC Pipe Sizer - Gas High Pressure 4. HVAC Pipe Sizer – Liquid 5. HVAC Pipe Sizer – Steam 6. Steam Tables 7. Psychrometric Plus 8. Psychrometric LT 9. HVAC Pipe Sizer Plus 10. HVAC Pipe Sizer Gas Plus 11. HVAC Toolkit 12. HVAC Toolkit Ultimate 13. HVAC Residential Load Calcs 14. HVAC Load Plus 15. HVAC Equipment Locator 16. ASHRAE Duct Fitting Database 17. ASHRAE 62.1 Ventilation Load Calcs 18. HVAC Psych HD 19. HVAC ResLoad-J 20. HVAC Residential Load Calcs HD
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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
axios
react-native-paper
Zustand
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.
