Gas technician calculators

Meter clocking: gas input (Btu/h)

Time one full turn of the test dial with only this appliance running. Time 2–3 turns and divide for a better reading.

Defaults: natural gas 1,000 Btu/ft³ (37.3 MJ/m³) and propane 2,500 Btu/ft³ (93.1 MJ/m³), the round numbers used in G2 course math. Enbridge’s actual Ontario gas averages about 38.9 MJ/m³ (about 1,040 Btu/ft³). For an exact figure, ask the gas supplier.

Formula: ft³/h = dial size (ft³) × 3600 ÷ seconds · Btu/h = ft³/h × heating value (Btu/ft³)

Furnace output, temperature rise and airflow (CFM)

Measure return air and supply air temperatures once the furnace has run long enough to be steady. Compare the rise with the range on the rating plate.

1.08 assumes standard air (about 70°F at sea level). Use it to get close to the manufacturer’s numbers, not as an exact measurement.

Formula: Output = input × efficiency · Temperature rise = supply − return · CFM = output (Btu/h) ÷ (1.08 × rise °F)

Pressure converter

Convert between inches of water column, psi, kPa, Pa, oz/in² and mbar.

Formula: 1 psi = 27.68 in. w.c. = 6.895 kPa · 1 in. w.c. = 249.1 Pa · 1 oz/in² = 1.73 in. w.c.

Heat and capacity converter

Convert Btu/h, kW, MBH, tons of cooling, boiler horsepower and MJ/h.

Some course material rounds one boiler horsepower to 34,000 Btu/h.

Formula: 1 kW = 3,412 Btu/h · 1 ton = 12,000 Btu/h · 1 boiler hp = 33,475 Btu/h · 1 MJ/h = 947.8 Btu/h

Temperature converter (°F ↔ °C)

Type in either box.

Formula: °C = (°F − 32) × 5 ÷ 9 · °F = °C × 9 ÷ 5 + 32

Ohm’s law and power

Fill in any two of voltage, current and resistance. Leave the third blank.

Formula: V = I × R · I = V ÷ R · R = V ÷ I · P (watts) = V × I