Describe the duct sections between furnace and stack and the equipment along the way to get ID fan pressure and flow and what a variable frequency drive saves.
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.
Items along the gas path, from furnace to stack, that the fan must overcome. Stack draft helps.
Damper or vane control compared with a variable frequency drive.
Cash flow of the improvement: investment in year 0 and annual savings escalated at the rate entered, discounted at the MARR.
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For each section, correct flow and density for temperature, compute velocity in the actual area and friction with the hydraulic diameter, and add bend and fitting losses with K coefficients. Then add equipment pressure drop.
About 40 to 65 ft/s (12 to 20 m/s) in steel ducts. Below about 26 ft/s ash and dust tend to settle; above 80 ft/s loss and erosion grow.
Almost always, when the fan spends much of its time below design flow with a throttled damper. Paybacks are usually 1 to 3 years.
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