Emissions equal fuel burned times an AP-42 factor
You do not need a stack test to put a number on combustion emissions. Emissions equal fuel burned multiplied by an emission factor, reduced by (1 − control efficiency) when a control device is installed. Fuel purchase records alone are enough to estimate annual NOx, SO₂, particulate and CO, which is how most minor source permit applications and emission inventories get built.
The defaults loaded here come from EPA AP-42 for small uncontrolled industrial boilers. Natural gas carries 100 lb NOx, 0.6 lb SO₂, 7.6 lb PM and 84 lb CO per million standard cubic feet. No. 2 distillate oil carries 20 lb NOx, 7.1 lb SO₂, 2 lb PM and 5 lb CO per thousand gallons, and No. 6 residual oil carries 55 lb NOx, 47.1 lb SO₂, 5.98 lb PM and 5 lb CO per thousand gallons.
Sulfur dioxide scales directly with fuel sulfur content. The oil values above assume 0.05 % sulfur in distillate and 0.3 % in residual, following the AP-42 relationships of 142 × S and 157 × S pounds per thousand gallons. If your fuel analysis shows a different sulfur level, scale the factor accordingly, which is why the factor field stays editable.
Treat the output as a planning estimate. Permitted sources report using the factors and test methods specified in the permit, and actual rates swing widely with burner design, low NOx equipment and firing rate. Values reflect AP-42 as of September 2026. Confirm applicable factors with your state or local air agency and have a qualified environmental professional review any submittal.
Frequently Asked Questions
It varies by design, but 40 to 70 % reduction is common. Rather than editing the factor, enter that reduction in the control efficiency field so the uncontrolled figure stays visible for comparison.
Yes, when you have it. Emission factors exist for sources without measurements. If a stack test is available, calculate mass rate from measured concentration and exhaust flow and use that.