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Plumbing & HVAC

Stack Effect Pressure Calculator

Stack effect pressure across an opening from its height off the neutral plane and the indoor-outdoor temperature difference, and the air speed it drives.

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How far the opening is below (or above) the level where inside and outside pressures are equal.

With openings spread evenly up a building the neutral plane sits near mid-height, so a door at floor level in a 12 m (39 ft) shed is about 6 m (20 ft) below it. Large openings low down pull the plane down towards them.

Sets the direction the air moves; the size of the pressure depends only on the height.

In a heated building air comes in below the neutral plane and goes out above it; in a building cooled below the outdoor temperature the flows reverse.

The air temperature inside the building.

For a warehouse, the temperature the heating holds; for a tall building, the average up its height.

The outdoor air temperature.

The design winter temperature for a heating check, or the day's temperature for a diagnosis.

How much of the ideal flow a real opening passes — about 0.65 for a large opening.

It sets only the air speed row; the pressure does not depend on it.

Stack pressure across the opening

5.21 Pa

Medium confidence

Outside air is pushed in through this opening: the building is warmer than outside and the opening is below the neutral plane, or cooler and above it. The pressure grows in a straight line with the height from the neutral plane and with the temperature difference.

The same pressure in inches of water gauge (in. w.g.)
0.02 in. w.g.
Outdoor air density
0.08 pcf
Air speed through the opening at this discharge coefficient
362.08 ft/min
Then change the inputs to see how far the answer moves.

Show calculation logic

How this was calculated

Formula source(s)

  • ASHRAE Handbook—Fundamentals, Chapter 16, Ventilation and Infiltration: stack pressure Δp = ρo × g × (H_NPL − H) × (Ti − To) ÷ Ti, temperatures absolute; flow through a large opening with a discharge coefficient of about 0.65
  • Outdoor air density from the ideal gas law: ρ = 101,325 Pa ÷ (287.055 J/kg·K × T), dry air at standard pressure

Inputs used

Height of the Opening From the Neutral Pressure Plane
19.5 ft
Where the Opening Is
Below the neutral plane — a door, a low vent
Inside Temperature
64.4 °F
Outside Temperature
28.4 °F
Discharge Coefficient of the Opening
0.65

Intermediate steps

The same pressure in inches of water gauge (in. w.g.)
0.02 in. w.g.
Outdoor air density
0.08 pcf
Air speed through the opening at this discharge coefficient
362.08 ft/min
Final result5.21 Pa

Confidence note: Outside air is pushed in through this opening: the building is warmer than outside and the opening is below the neutral plane, or cooler and above it. The pressure grows in a straight line with the height from the neutral plane and with the temperature difference.

What this calculation does not cover

  • The neutral plane's position is an estimate: mid-height for evenly spread openings, lower when the large openings are low. Wind adds its own pressures on top, and on an exposed door it can dominate.
  • The air speed is an order-of-magnitude figure. Discharge coefficients vary with the opening's shape, and flow through a large door is two-way — out at the top while it comes in at the bottom.
  • Mechanical ventilation that holds the building above or below outside pressure moves the neutral plane and can reverse the flow at a given opening.

Add the equipment this sizes

This result is a specification — 5.21 Pa — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

19.5 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Sources checked 2026-09-22 · v1.0.0

Regulatory standards & verification citations2
  1. ASHRAE Handbook—Fundamentals, Chapter 16, Ventilation and Infiltration: stack pressure Δp = ρo × g × (H_NPL − H) × (Ti − To) ÷ Ti, temperatures absolute; flow through a large opening with a discharge coefficient of about 0.65
  2. Outdoor air density from the ideal gas law: ρ = 101,325 Pa ÷ (287.055 J/kg·K × T), dry air at standard pressure
Cite this page

Your workspace

Most jobs need more than one number. Add the calculators you need next and they open right here, underneath this one — your figures stay on screen and nothing is lost to a page change.

Now that you have the number

These guides cover the work this quantity is for — the first ones run this calculator inside the section that raises the question.

  • Heating a High-Bay Warehouseuses this calculator

    Sizing heat for a tall shed whose doors cycle all day: where the setpoint applies, why the stack effect beats the fabric, and radiant against warm air.

How to calculate stack effect pressure in 6 steps

  1. Height of the Opening From the Neutral Pressure PlaneHow far the opening is below (or above) the level where inside and outside pressures are equal.
  2. Where the Opening IsSets the direction the air moves; the size of the pressure depends only on the height.
  3. Inside TemperatureThe air temperature inside the building.
  4. Outside TemperatureThe outdoor air temperature.
  5. Discharge Coefficient of the OpeningHow much of the ideal flow a real opening passes — about 0.65 for a large opening.
  6. Stack pressure across the openingThe tool computes the stack pressure across the opening from those figures and shows the formula, its sources, and a confidence rating alongside it.

Stack pressure across the opening by height of the opening from the neutral pressure plane

Page defaults, not your figures above.

Height of the Opening From the Neutral Pressure PlaneStack pressure across the opening (Pa)
10 ft2.67
15 ft4.01
20 ft5.35
25 ft6.68
30 ft8.02
35 ft9.36

Frequently asked questions

Why does an open dock door cost so much heat?
Because a few pascals across a large opening move a great deal of air. The guide's 12 m (39 ft) shed with 20 K (36 °F) across its walls sees about five pascals at floor level, enough to drive roughly two metres a second (400 ft/min) inward across the bottom of an open door — tens of thousands of cubic metres an hour to be heated through that difference.
Where is the neutral pressure plane?
Where the inside and outside pressures are equal. With leakage spread evenly it sits near mid-height; a big opening low down pulls it down, and a building held above outside pressure by its ventilation shifts it too. Above it air leaves the building in winter; below it air comes in.
Why are the temperatures absolute?
Because the effect comes from the difference in air density, and density follows the absolute temperature. The formula divides by the indoor temperature in kelvin, which is why the same 20 degrees does slightly more on a cold day than on a mild one.
Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.