Advanced Rocket Stove Inputs
Example Data Table
| Design Type | Core Area | Feed Height | Burn Tunnel | Riser Height | Typical Use |
|---|---|---|---|---|---|
| Small cooking stove | 64 cm² | 15 cm | 30 cm | 60 cm | Single pot meals |
| Medium field stove | 100 cm² | 18 cm | 36 cm | 95 cm | Daily outdoor cooking |
| Large heating core | 144 cm² | 24 cm | 48 cm | 120 cm | High heat demand |
Formula Used
Cross sectional area: Area = width × depth
Equivalent round diameter: D = √(4A ÷ π)
J-core ratio check: Feed height : burn tunnel length : riser height ≈ 1 : 2 : 3
Net fuel energy: Net MJ/kg = dry fuel energy × dry fraction − 2.44 × moisture fraction
Fuel rate: kg/hour = heat kW × 3.6 ÷ (net energy × efficiency)
Draft estimate: Draft Pa = 3465 × height × (1/Tambient − 1/Tflue)
Pot skirt exhaust area: π × ((pot radius + gap)² − pot radius²)
How to Use This Calculator
Choose your unit system first. Enter all channel sizes using the same system. Add fuel moisture, expected heat output, and burn time. Use dry fuel for better accuracy. Then enter feed tube, burn tunnel, heat riser, pot gap, and chimney details.
Press the calculate button. The result appears above the form. Review the design score, working core area, fuel use, draft pressure, and warnings. A good stove keeps all internal cross sections close. The pot skirt and chimney should not choke the gases.
Use the CSV button for spreadsheet records. Use the PDF button for a compact field report. Recalculate after changing any major dimension.
Rocket Stove Design Guide
Why Dimensions Matter
A rocket stove works through balance. Air enters the feed tube. Fuel burns inside a short tunnel. Hot gases then rise through an insulated riser. Each part must support the same flow. If one section is smaller, it becomes a restriction. Smoke can return through the feed tube. Heat output can also fall quickly.
Core Area and Ratios
The calculator compares feed tube, burn tunnel, and riser areas. A strong design keeps them close. The smallest area becomes the working core area. This value controls flow, draft, and gas speed. Many J-core designs follow a simple length pattern. The feed tube is one part. The burn tunnel is about two parts. The heat riser is about three parts.
Fuel, Heat, and Air
Fuel quality changes performance. Wet fuel wastes heat because water must evaporate. The calculator reduces fuel energy when moisture rises. It then estimates fuel burned per hour. It also estimates combustion air. This helps you judge whether the stove has enough open area for clean burning.
Draft and Chimney Flow
Draft comes from hot gas rising. Taller and hotter risers produce stronger draft. A short riser can feel weak. A narrow chimney can also slow the stove. The tool checks chimney area against the core area. It also checks the pot skirt gap. Both paths must pass gases without choking the flame.
Material Planning
Insulation keeps heat inside the riser. This supports cleaner combustion and faster draft. The calculator estimates insulation volume and mass. Use this value for planning clay, perlite, vermiculite, refractory mix, or light insulation. Always test safely outdoors before indoor or enclosed use.
FAQs
What is a rocket stove calculator?
It estimates stove core dimensions, fuel use, air demand, draft, chimney size, and pot gap. It helps compare design choices before building.
What ratio is used for the stove core?
This tool checks the common J-core pattern of 1:2:3. That means feed height, burn tunnel length, and riser height are compared.
Why should the areas be equal?
Equal cross sections help gases move smoothly. A narrow section can reduce draft, create smoke, and lower heat transfer.
Does fuel moisture affect the result?
Yes. Wet fuel has lower usable energy. The calculator reduces net heat value as moisture increases, so fuel demand rises.
What is a good design score?
A score above 80 usually means the entered dimensions are well balanced. Still, real stoves need safe outdoor testing.
Why is pot skirt gap important?
The gap lets hot gases escape around the pot. If it is too small, it can choke flow and increase smoke.
Can I use imperial units?
Yes. Select the imperial option. Enter dimensions in inches, heat in BTU per hour, and density in pounds per cubic foot.
Is this enough for final construction?
No. Use it for planning and comparison. Follow local safety rules, use heat-safe materials, and test the stove outdoors first.