Ontario G3 Gas Technician exam preparation
Home › Gas properties
The figures that appear on nearly every attempt. Learn these cold and a meaningful share of the exam becomes free marks.
| Property | Natural gas | Propane |
|---|---|---|
| Heat content | ~1,000 Btu/ft³ | ~2,520 Btu/ft³ |
| Specific gravity | ~0.55 — lighter than air | ~1.52 — heavier than air |
| Flammability limits | 4% – 14% | 2.4% – 9.5% |
| Boiling point | −162 °C / −260 °F | −42 °C / −44 °F |
| Air for combustion | ~10 ft³ per ft³ gas | ~25 ft³ per ft³ gas |
| Maximum CO₂ | 11.9% | 13.7% |
Air is taken as 1.00 for specific gravity. That single line explains why a natural gas leak collects at ceiling level and a propane leak collects at floor level — a distinction the exam tests in several forms.
Roughly 0.55, which makes it lighter than air. Propane vapour is about 1.52 and therefore heavier than air, which is why the two behave so differently when they escape.
Natural gas burns between roughly 4% and 14% in air. Propane is narrower and lower, at roughly 2.4% to 9.5%.
About 10 cubic feet of air per cubic foot of natural gas. Propane needs far more — about 25 cubic feet per cubic foot of gas.
1 PSI equals 27.68 inches water column. Going the other way, 1 inch water column is about 0.0361 PSI.