Chimney Draft Calculator
Stack effect draft from height and temperature.
Enter your values
Enter the chimney height in ft.
Enter the flue gas temp in °F.
Enter the outdoor temp in °F.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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.
ΔP ≈ 0.0188 x h x (1/To - 1/Ti) in wc (Rankine)
At a glance
| What it does | Stack effect draft from height and temperature. |
|---|---|
| Category | HVAC & Airflow |
| Inputs needed | Chimney height, Flue gas temp, Outdoor temp |
| Main output | Theoretical draft |
| Formula | ΔP ≈ 0.0188 x h x (1/To - 1/Ti) in wc (Rankine) |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Chimney height(ft)
- Enter the chimney height in ft.
- Flue gas temp(°F)
- Enter the flue gas temp in °F.
- Outdoor temp(°F)
- Enter the outdoor temp in °F.
Worked example
Using the values the calculator loads with:
Inputs
- Chimney height20 ft
- Flue gas temp350 °F
- Outdoor temp40 °F
Results
- Theoretical draft0.288 in wc
- In Pa71.8
- Temperature difference310 °F
- RatingAdequate for most appliances
- Reference figure0.008
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.
What do I need to enter into the Chimney Draft Calculator?
Just 3 values: chimney height, flue gas temp, outdoor temp. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Chimney Draft Calculator work out the answer?
Natural draft grows with chimney height and with how much hotter the flue gases are than outdoor air. It applies the formula ΔP ≈ 0.0188 x h x (1/To - 1/Ti) in wc (Rankine) and shows the working so you can check each step by hand.
Is the Chimney Draft Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.