Accurate orifice sizing for outdoor garden appliances. Supports natural gas and propane with unit flexibility. Designed for safe burners, heaters, and CO2 systems today.
| Gas | Heat Input | P1 | P2 | Temp | Cd | k | Typical Output |
|---|---|---|---|---|---|---|---|
| Natural Gas | 50,000 BTU/hr | 7 inH2O(g) | 3.5 inH2O(g) | 70 °F | 0.62 | 1.30 | Orifice diameter in mm/in |
| Propane | 40,000 BTU/hr | 11 inH2O(g) | 10 inH2O(g) | 70 °F | 0.62 | 1.13 | Smaller diameter due to higher energy density |
This calculator estimates the required orifice area by treating the orifice as a restriction with discharge coefficient Cd.
Reference model: standard compressible orifice relationships and expansibility concepts used in engineering practice. Always validate with appliance manufacturer data and local codes.
Garden gas appliances include patio heaters, fire features, outdoor kitchens, and greenhouse CO₂ burners. Each device needs stable flames across wind and temperature swings. Correct orifice sizing balances heat output, noise, and ignition reliability while keeping manifold pressure within the regulator’s range. Oversized jets waste fuel, while undersized jets cause weak flames and delayed ignition.
Heat input or standard flow sets the target energy delivery. Upstream pressure comes from the regulator, while downstream pressure represents the burner manifold. Gas temperature affects density and sonic velocity. Gas properties—molecular weight, heating value, and k—shift mass flow and the critical pressure ratio used in compressible calculations. If you lack lab data, start with common values and refine after testing.
When P2/P1 drops below the critical ratio, the calculator flags choked flow. In this regime the jet reaches sonic conditions and additional downstream restriction cannot increase flow. If the result is subsonic, flow responds to changes in P2, so burner tuning and manifold losses matter more. Use the drill-size hint to choose a practical bit near the computed diameter. A small step change is safer than a large jump in diameter.
Installations should use approved jets, clean burr-free holes, and consistent thickness at the orifice plate. Avoid drilling soft metals without proper fixturing because eccentric holes change Cd. Keep inlet strainers clean, check for water and oil contamination, and confirm that hose length and fittings do not starve the burner under full load. For multi-burner manifolds, verify pressure at the farthest branch.
Use the CSV and PDF exports to capture assumptions, units, and calculated diameter. After installation, verify flame color, stability, and appliance rating plate limits. Perform leak checks at every connection, measure manifold pressure with a manometer, and document any adjustments so future maintenance restores the same safe performance consistently. When possible, compare against manufacturer orifice charts for the specific burner family.
1) Which flow input should I use for a patio heater?
If the appliance rating is in BTU per hour, choose heat input and enter the rating. If you have gas meter data or supplier flow, choose SCFH or Nm³/h to match that source.
2) What pressures should I enter for low-pressure outdoor systems?
Use the regulator outlet pressure for upstream and the burner manifold pressure for downstream. Many natural gas systems are around 7 inH2O supply with 3 to 4 inH2O at the manifold, but verify your equipment.
3) Why does the calculator show choked flow?
Choked flow occurs when downstream pressure is low enough that the jet reaches sonic conditions. In that case, increasing downstream restriction will not increase flow; you must change upstream pressure, gas properties, or orifice size.
4) Is the drill-size suggestion a final specification?
No. It is a practical nearest size for prototyping and understanding. For production, use manufacturer jets or precision drilling and verify combustion performance under real operating conditions.
5) How do I use the existing-orifice capacity check?
Enable the option, enter your current orifice diameter, then submit. The calculator estimates the standard flow and heat input that orifice would pass at your selected pressures and gas properties.
6) What safety steps should follow any orifice change?
Leak test all joints, confirm ventilation, and measure manifold pressure with a manometer. Observe flame stability and color, and ensure the appliance stays within its rated input. When in doubt, consult a qualified gas technician.
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.