Chimney Draft Calculator
Stack effect draft from height and temperature.
Reviewed by James Whitfield · How we check our maths
Your values
ⓘ Live results
Results
- Theoretical draft
- 0.288 in wc
- In Pa
- 71.8
- Temperature difference
- 310 °F
- Rating
- Adequate for most appliances
- Reference figure
- 0.008
Quick answer
Natural draft grows with chimney height and with how much hotter the flue gases are than outdoor air.
The formula
ΔP ≈ 0.0188 x h x (1/To - 1/Ti) in wc (Rankine)
Worked example
Worked example
Using the values the calculator loads with.
Inputs
- Chimney height20 ft
- Flue gas temp350 °F
- Outdoor temp40 °F
Result
- Theoretical draft0.288 in wc
- In Pa71.8
- Temperature difference310 °F
- RatingAdequate for most appliances
- Reference figure0.008
How to use the Chimney Draft Calculator
- 1Measure the vertical height from the appliance outlet to the flue top.
- 2Estimate flue gas temperature — 300-400°F is typical for a wood stove.
- 3Compare against the appliance's required draft, usually 0.04-0.10 in wc.
Frequently asked questions
Why is my stove smoking?
Short flue, cold chimney or a house held negative by exhaust fans are the usual causes.
Does a liner help?
Yes — a correctly sized insulated liner keeps gases hotter and draft stronger.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error