Furnace Draft Loss Calculator
Reviewed by Hamza Gujjar, Algorithm Architect & Software Developer
Last updated: July 26, 2026Furnace Draft Loss Calculator
Flue gas has to fight resistance at every stage of its journey - through the furnace passes, across the economizer, and up the stack - and a draft fan has to be sized against the sum of all of it.
Formula: Total Draft Loss = furnace pass loss + economizer loss + stack loss
Example: 150 Pa through the furnace passes, 80 Pa across the economizer, and 40 Pa up the stack sums to 270 Pa total.
How to Use This Calculator
- Enter the pressure loss through the furnace passes.
- Enter the pressure loss across the economizer.
- Enter the stack pressure loss.
An induced or forced draft fan needs to overcome this entire total, typically with an added margin for fouling that builds up in heat transfer surfaces over time.