Gas Orifice Conversion Chart
Gas Orifice Size Conversion for Natural and LP Gas
Understanding the Gas Orifice Conversion Chart
This gas orifice conversion chart is designed to assist HVAC professionals, mechanical contractors, and homeowners who want to convert gas appliances from one type of gas to another. Use this chart to find the correct orifice size to make sure the appliance burns the new gas type efficiently and safely.
Why Gas Orifice Size Matters
An orifice controls the flow of gas into a gas burner, directly affecting combustion quality and energy efficiency. An incorrectly sized orifice can lead to improper combustion, resulting in energy waste, reduced appliance performance, and potential safety hazards.
Working With The Gas Orifice Conversion Chart
The gas orifice conversion chart below is divided into two main sections: Natural Gas (1050 BTU/cu ft, 0.65 SP.GR.) and LP Gas (2500 BTU/cu ft, 1.53 SP.GR.). Here’s how to use it:
- Orifice Size (Drill Size): The left column shows the drill size that corresponds to the diameter of the hole required for the gas orifice. For example, when converting a propane furnace to natural gas, you’ll need to increase the diameter of the hole because natural gas operates at a lower pressure. This means that a larger orifice is necessary to maintain the correct gas flow rate and prevent underfiring.
- Conversion Values: The chart provides BTU values for various pressures (in inches of water column) for both Natural and LP Gas. These values will help you determine the correct orifice size needed to achieve a specific BTU output per burner at a given pressure.
Always consult with a professional before making adjustments to gas orifices. Incorrect modifications can lead to unsafe operating conditions.
| Natural Gas BTUs/hr | LP | |||||||
|---|---|---|---|---|---|---|---|---|
| Drill Size | In Decimals | Inches W.C. > | 3 | 3.5 | 4 | 4.5 | 7.0 | 11.0 |
| 80 | 0.0135 | 428 | 463 | 495 | 525 | 654 | 1,273 | |
| 79 | 0.0145 | 494 | 534 | 571 | 605 | 755 | 1,469 | |
| 1/64 | 0.0156 | 572 | 618 | 661 | 701 | 874 | 1,700 | |
| 78 | 0.016 | 602 | 650 | 695 | 737 | 919 | 1,788 | |
| 77 | 0.018 | 762 | 823 | 879 | 933 | 1,163 | 2,263 | |
| 76 | 0.020 | 940 | 1,016 | 1,086 | 1,152 | 1,436 | 2,794 | |
| 75 | 0.021 | 1,037 | 1,120 | 1,197 | 1,270 | 1,583 | 3,081 | |
| 74 | 0.0225 | 1,190 | 1,285 | 1,374 | 1,457 | 1,818 | 3,536 | |
| 73 | 0.024 | 1,354 | 1,462 | 1,563 | 1,658 | 2,068 | 4,024 | |
| 72 | 0.025 | 1,469 | 1,587 | 1,696 | 1,799 | 2,244 | 4,366 | |
| 71 | 0.026 | 1,589 | 1,716 | 1,835 | 1,946 | 2,427 | ,4722 | |
| 70 | 0.028 | 1,843 | 1,991 | 2,138 | 2,257 | 2,815 | 5,476 | |
| 69 | 0.0292 | 2,004 | 2,165 | 2,314 | 2,455 | 3,062 | 5,915 | |
| 68 | 0.031 | 2,259 | 2,440 | 2,609 | 2,767 | 3,451 | 6,713 | |
| 1/32 | 0.0313 | 2,303 | 2,487 | 2,669 | 2,828 | 3,518 | 6,843 | |
| 67 | 0.032 | 2,400 | 2,595 | 2,779 | 2,948 | 3,677 | 7,153 | |
| 66 | 0.033 | 2,560 | 2,765 | 2,956 | 3,135 | 3,909 | 7,607 | |
| 65 | 0.035 | 2,860 | 3,085 | 3,296 | 3,493 | 4,357 | 8,468 | |
| 64 | 0.036 | 3,046 | 3,291 | 3,518 | 3,731 | 4,654 | 9,053 | |
| 63 | 0.037 | 3,216 | 3,470 | 3,707 | 3,921 | 4,891 | 9,563 | |
| 62 | 0.038 | 3,394 | 3,666 | 3,919 | 4,157 | 5,185 | 10,087 | |
| 61 | 0.039 | 3,575 | 3,862 | 4,132 | 4,380 | 5,464 | 10,625 | |
| 60 | 0.040 | 3,761 | 4,062 | 4,343 | 4,606 | 5,745 | 11,176 | |
| 59 | 0.041 | 3,951 | 4,268 | 4,563 | 4,840 | 6,036 | 11,742 | |
| 58 | 0.042 | 4,147 | 4,479 | 4,788 | 5,078 | 6,334 | 12,322 | |
| 57 | 0.043 | 4,346 | 4,695 | 5,011 | 5,323 | 6,639 | 12,916 | |
| 56 | 0.0465 | 5,083 | 5,490 | 5,869 | 6,225 | 7,764 | 15,104 | |
| 3/64 | 0.0469 | 5,171 | 5,585 | 5,970 | 6,333 | 7,898 | 15,365 | |
| 55 | 0.052 | 6,356 | 6,865 | 7,339 | 7,785 | 9,709 | 18,888 | |
| 54 | 0.055 | 7,111 | 7,680 | 8,211 | 8,709 | 10,862 | 21,131 | |
| 53 | 0.0595 | 8,322 | 8,989 | 9,609 | 10,192 | 12,712 | 24,730 | |
| 1/16 | 0.0625 | 9,182 | 9,918 | 10,603 | 11,246 | 14,026 | 27,286 | |
| 52 | 0.0635 | 9,478 | 10,238 | 10,945 | 11,609 | 14,479 | 28,167 | |
| 51 | 0.067 | 10,552 | 11,398 | 12,184 | 12,924 | 16,119 | 31,357 | |
| 50 | 0.07 | 11,518 | 12,441 | 13,300 | 14,107 | 17,594 | 34,228 | |
| 49 | 0.073 | 12,527 | 13,530 | 14,464 | 15,342 | 19,135 | 37,225 | |
| 48 | 0.076 | 13,577 | 14,665 | 15,678 | 16,629 | 20,740 | 40,347 | |
| 47 | 0.0785 | 14,485 | 15,646 | 16,726 | 17,741 | 22,127 | 43,045 | |
| 5/64 | 0.0781 | 14,338 | 15,487 | 16,556 | 17,560 | 21,902 | 42,608 | |
| 46 | 0.081 | 15,423 | 16,658 | 17,809 | 18,889 | 23,558 | 45,831 | |
| 45 | 0.082 | 15,806 | 17,072 | 18,251 | 19,358 | 24,144 | 46,969 | |
| 44 | 0.086 | 17,385 | 18,778 | 20,075 | 21,293 | 26,557 | 51,663 | |
| 43 | 0.089 | 18,620 | 20,111 | 21,500 | 22,804 | 28,442 | 55,331 |
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