Balance air streams to support low-smoke burning. Ideal for compost heaters, biochar kilns, and stoves. Enter flows, view ratios instantly, and save reports anywhere.
Calculate secondary air share for garden burners quickly. Compare primary and secondary flows, units included easily. Export results to files and tune airflow settings today.
| # | Primary | Secondary | Total | Secondary ratio (%) | Secondary/Primary |
|---|---|---|---|---|---|
| 1 | 120.0 | 60.0 | 180.0 | 33.33 | 0.500 |
| 2 | 80.0 | 40.0 | 120.0 | 33.33 | 0.500 |
| 3 | 150.0 | 100.0 | 250.0 | 40.00 | 0.667 |
| 4 | 60.0 | 30.0 | 90.0 | 33.33 | 0.500 |
| 5 | 200.0 | 50.0 | 250.0 | 20.00 | 0.250 |
Secondary air ratio expresses how much of the total airflow is injected as secondary air.
T = P + SR% = (S / T) × 100S/P = S ÷ PS = T × (R%/100), P = T − SS = (r×P)/(1−r) where r = R%/100Secondary air improves mixing above the fuel bed, supporting cleaner burn and steadier heat. In garden heaters, biochar kilns, and small incinerators, staged air helps complete oxidation of volatiles that would otherwise smoke. The calculator quantifies how much of total airflow is delivered as secondary air, enabling repeatable tuning across different fuels and weather conditions. For compost heat units, improved burn lowers odor complaints and ash handling.
Use one consistent unit for all inputs and keep fan settings fixed during measurement. Simple methods include inline anemometer readings at a duct, calibrated orifice plates, or manufacturer fan curves corrected for static pressure. Record where measurements are taken, because leaks and duct restrictions change delivered flow. Enter the measured primary and secondary values, or use total flow with a target percentage. Take three readings and average to reduce gust and turbulence error in humid, windy outdoor setups.
The secondary ratio is S divided by total flow (P plus S), expressed as a percent. It answers, “What share of all air is injected above the flame?” The secondary‑to‑primary ratio, S/P, is useful when comparing designs with different totals. Higher ratios generally increase mixing and burn-out, but excessive secondary air can cool the flame and reduce draft. Use results alongside temperature and smoke observations for balanced decisions.
Start with conservative secondary percentages, then observe flame stability, smoke color, and residue. If smoke persists after warm-up, raise secondary flow or redistribute jets for better coverage. If temperature drops or flame lifts off ports, reduce secondary flow or increase primary slightly. Re-check the ratio after cleaning screens, replacing blowers, or changing duct lengths, because system resistance shifts flows.
Exporting CSV and PDF results supports maintenance logs and seasonal setup notes. Save the measured flows, calculated ratios, and any observed outcomes such as odor, soot, or char quality. Over time, these records help set standard operating ranges for different feedstocks, moisture levels, and ambient conditions. Consistent documentation also aids troubleshooting when performance changes unexpectedly.
It is the percentage of total airflow delivered as secondary air above the flame. It helps you compare setups and repeat a clean-burning air staging target across seasonal changes.
Start with a modest secondary share, then adjust using smoke, flame stability, and temperature. Many small garden burners respond well to incremental changes of five percentage points.
No. Use the same unit for all airflow values, then select the matching label. Mixing units makes totals and ratios incorrect, even if the numbers look reasonable.
When primary airflow is zero, dividing by primary is undefined. The calculator still reports the secondary percentage of total and the total airflow for documentation.
Use a fan curve with measured static pressure, or a simple timed bag fill method for low flows. Whatever method you use, repeat it consistently for comparable ratios.
Not always. Too much secondary air can cool the flame and weaken draft, increasing unburned gases. Aim for balanced mixing, adequate temperature, and stable combustion behavior.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.