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Chimney Draft Calculator

Calculate chimney draft pressure instantly with our free Chimney Draft Calculator. Get accurate results for flue gas, height, and airflow.

J/(kg·K)
m/s²

A chimney works because warm gas rises. This rise creates a pull called draft. It helps smoke move out of a home, furnace, or boiler. But the draft changes with heat, height, and air pressure. That’s why we built a simple Chimney Draft Calculator. It gives you the draft pressure in a flash. You won’t need math skills. You won’t need long steps. You’ll only enter a few values and get clear results.

This tool works for homes, fire pits, stoves, heaters, and even industry systems. It shows real draft values based on the stack effect. You’ll feel like you're solving a big problem with a small tap.

How the Chimney Draft Works

Hot gas is light. Cold air is heavy. When hot gas rises inside a chimney, the heavy air outside pushes it upward. This difference makes the draft. A taller chimney pulls stronger. Hotter gas pulls harder. Cooler outside air helps too.

Think of it like a balloon. Warm air lifts. Cold air drops. A chimney follows the same idea.

Chimney Draft Calculation Formula

Here’s the same formula used by engineers, shown in simple text form:

Density of ambient air:

rho_a = P / (R × T_a)

Density of flue gas:

rho_g = P / (R × T_g)

Draft pressure:

Delta_P = g × h × (rho_a − rho_g)

Where:

  • P = pressure
  • R = gas constant
  • T_a = outside air temp in Kelvin
  • T_g = flue gas temp in Kelvin
  • g = gravity
  • h = chimney height

Draft in mmH2O = Delta_P / 9.80665

Draft in inch H2O = Draft_mm / 25.4

Draft in kPa = Delta_P / 1000

Draft in psi = Delta_P / 6894.76

The calculator uses this full formula but hides the complex math. You’ll only see clean and simple output.

How to Use the Chimney Draft Calculator

Enter the chimney height. Pick the unit you want. Add the air pressure. Add the outside air temperature. Add the flue gas temperature. Hit the calculate button. The draft result shows at once.

You’ll see the draft in Pa, mmH2O, inH2O, kPa, and psi. That gives you full control. It helps you design or test any chimney setup with ease.

Final Verdict

The Chimney Draft Calculator is simple and smart. It helps you check draft pressure fast with easy steps. It boosts safety. It boosts heat flow. It makes chimney work easier to understand. If you want a clear draft reading without deep math, this tool is your best friend.

FAQs

What is chimney draft?

Chimney draft is the pull or suction that moves hot gas up a chimney. Heat creates lift, so the gas flows upward.

Why does draft matter?

Good draft keeps smoke out of your room. It boosts airflow and makes your fire burn cleaner.

Do taller chimneys pull better?

Yes. A taller chimney gives more pull because the pressure difference gets bigger.

Does temperature change the draft?

Yes. Hotter gas rises faster. It makes the draft stronger.

Can I use this tool for a wood stove?

Yes. It works for wood stoves, boilers, heaters, factories, and home chimneys.

Does high outside air pressure change the draft?

It can. More pressure changes the density of air, which changes the draft. The calculator handles this for you.