Set burner air shutters for clean heat. Use fuel, altitude, and throat size inputs simple. Review airflow, then adjust until the flame stabilizes safely.
This calculator estimates a starting air shutter opening by converting burner heat input into fuel flow, then into combustion-air demand. It applies an excess-air target and corrects for thinner air at altitude and warmer temperatures.
Fuel properties and targets are typical values. Real appliances vary, so treat results as a starting point and fine-tune with O₂/CO when available.
| Fuel | BTU/hr | Altitude | Temp | Throat | Excess air | Suggested opening |
|---|---|---|---|---|---|---|
| Natural gas | 80,000 | 0 m | 20 °C | 45 mm | 30% | ~45–55% |
| Propane | 60,000 | 1,000 m | 10 °C | 40 mm | 35% | ~55–70% |
| Natural gas | 120,000 | 500 m | 30 °C | 55 mm | 25% | ~35–50% |
Example rows are illustrative, not a substitute for appliance-specific tuning.
Combustion air controls how completely fuel burns. In greenhouse heaters, a stable blue flame reduces soot that can coat heat exchangers and restrict airflow. Proper primary air also lowers carbon monoxide risk and helps deliver repeatable heat output. Seasonal changes in temperature and elevation effects mean a single factory mark may not stay optimal. Efficient combustion also protects plants by avoiding fumes and uneven heater cycling.
This calculator converts heater input into estimated fuel flow, then multiplies by typical stoichiometric air demand for the selected fuel. It adds your excess-air target to provide margin for mixing and venting. Altitude and ambient temperature adjust air density, because thinner air needs more volume to carry the same oxygen mass. Throat diameter and usable opening fraction translate airflow into an estimated shutter area requirement. Humidity and intake screens can also change real airflow slightly.
The opening percent represents shutter area relative to usable throat area. If the value nears 100%, geometry may be limiting or assumed air velocity may be low. If it is very small, confirm burner input, throat measurement, and fuel selection. Use the starting mark for repeatable adjustments.
Use the result as a starting mark, then fine-tune. Yellow tips, odor, or soot generally indicate insufficient air; open slightly and recheck. Flame lift-off or harsh roaring can indicate excess air or strong draft; close slightly. If you have analyzer readings, keep CO low and use O₂ to guide small trims. Make changes in small steps and allow the heater to stabilize before judging.
Record settings after successful tuning and export a CSV or PDF for future service. Recheck after cleaning burners, replacing orifices, changing fuel supply pressure, or modifying venting. Inspect air inlets for dust and insects, and verify that greenhouse ventilation does not create unusual drafts across the burner.
It is an adjustable opening that controls how much primary air mixes with fuel before ignition. Changing the shutter affects flame color, stability, and emissions.
Burner input, fuel type, throat diameter, and your excess-air target drive the base airflow. Altitude and temperature refine the airflow because air density changes with conditions.
Higher altitude air is less dense, so the same shutter area delivers less oxygen mass. Opening the shutter increases the volume of air drawn in for similar combustion.
Enter analyzer readings to guide small adjustments. Higher CO or low O₂ typically means more air is needed. Very high O₂ may allow a slight reduction, if CO stays low.
Lifting can indicate too much primary air, strong draft, or incorrect pressure. Close the shutter slightly and confirm venting and burner condition before making larger changes.
Retune after cleaning the burner, changing orifices, adjusting gas pressure, or modifying venting. Also recheck at the start of each heating season and after major weather changes.
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.