From fuel, firing rate and O₂, find how much gas leaves the boiler or furnace, the temperature at which it condenses and whether the stack has enough draft or needs an ID fan.
Pre-sizing and estimating tool: results do not replace design, calculations or reports signed by a licensed professional, nor verification against the applicable codes and standards.
Natural draft, friction and fitting losses and the net draft available at the base, for the diameter entered.
Excess air increases gas flow, velocity and stack heat loss.
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Theoretical air comes from the fuel analysis, and measured O₂ gives the excess air. Adding CO₂, water, SO₂, N₂ and O₂ per kg (lb) of fuel and multiplying by the firing rate gives the flow in Nm³/h or scfm. Actual flow is larger because the gas is hot.
With sulfur-bearing fuels, keep metal walls 18 to 36 °F above the acid dew point. With natural gas and biomass, the limit is usually the water dew point unless the stack is built for condensation.
When natural draft, minus friction and fitting losses, cannot provide the suction the furnace and breeching require. An induced draft fan then makes up the difference.
Important notice: Indus Metrics tools produce estimates and pre-sizing results from the data you enter and from published engineering methods. They do not replace design, calculations or reports signed by a licensed professional engineer (PE), nor verification against the applicable codes, standards and regulations, such as OSHA rules and the ASME codes. Material and fuel properties vary: check manufacturer data or your own process analyses before deciding. By using this site you agree to the Terms of Use.
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