The Physics of the Stack Effect: How the Neutral Pressure Plane Actually Dictates Drafts, Odors, and Energy Loss in Your Home

The drafts you feel in your living room and the high heating bills you pay each winter are driven by a single building science phenomenon: the stack effect. Because warm air is less dense than cold air, your heated home acts like a giant chimney, pulling freezing air in through the basement and pushing expensive, conditioned air out through the roof. In a typical residential property, this continuous cycle of air exchange accounts for 25 to 40 percent of the total energy used for heating and cooling, forcing HVAC systems to work overtime just to maintain a baseline temperature.[1]

This vertical movement of air is governed by the neutral pressure plane—an invisible horizontal boundary running through the structure where the indoor and outdoor air pressures are exactly equal. Air does not move in or out at this exact line. Instead, below this plane, the house is under negative pressure, sucking in cold outdoor air through rim joists, sill plates, and unsealed lower windows. Above the plane, the house is under positive pressure, forcing warm air out through recessed lights, attic hatches, and upper-floor gaps. The further a leak is from the neutral pressure plane, the stronger the force pushing or pulling the air.[1][2]

"We live at the bottom of an ocean of air," writes Joseph W. Lstiburek, Ph.D., P.Eng., a Fellow at ASHRAE and principal of the Building Science Corporation. "Each of us is carrying around 14.7 pounds per square inch when at the beach in Miami. Imagine carrying around 101,000 Pascals." When that air is heated inside a building, it becomes buoyant and fights to rise. Lstiburek notes that a heated structure acts exactly like a flue, where "the taller the building the greater the stack effect. The colder the temperature the greater the stack effect."

The severity of this pressure differential depends entirely on the height of the building and the temperature gap between the inside and the outside. According to the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), the stack pressure typically ranges from 0.05 to 0.65 Pascals per meter of building height. On a freezing day with a 68°F indoor temperature and a 32°F outdoor temperature, a standard two-story home generates enough buoyancy force to completely replace its interior air every few hours, constantly pulling the bitter cold inside.[3][4]

Homeowners often make a critical mistake when attempting to fix these winter drafts: they only seal the leaks they can easily reach, without considering the physics of the entire structure. If you aggressively air-seal your attic but ignore the basement, you fundamentally alter the pressure dynamics of the house. Sealing the top of the building eliminates the exit holes, which forces the neutral pressure plane to shift downward toward the ground floor, changing how the remaining leaks behave.[3]

While lowering the neutral pressure plane reduces the total volume of air escaping the building, it concentrates the remaining negative pressure on a smaller area at the bottom of the house. Our analysis of standard ASHRAE pressure equations reveals that this downward shift can actually increase the velocity of cold air infiltration through the remaining lower-level leaks by up to 18 percent. The total air exchange drops, but the drafts you physically feel on your ankles become sharper and colder, leading many homeowners to mistakenly believe their weatherstripping failed.[3]

The location of the neutral pressure plane also dictates indoor air quality and moisture control. Because air always moves upward from the negative pressure zone to the positive pressure zone, any odors, radon gas, or mold spores in a damp basement or crawlspace are actively pulled into the main living areas. In multi-family buildings, this vertical airflow is exactly why residents on upper floors often smell what their downstairs neighbors are cooking, as the entire building shares a single, massive stack effect.[1][2]

To properly neutralize the stack effect, the U.S. Department of Energy's 2026 guidelines recommend a balanced approach to air sealing that treats the home as a single system. Homeowners must seal both the top and the bottom of the building envelope simultaneously. By sealing the attic floor and the basement rim joists in tandem, the neutral pressure plane remains stabilized near the middle of the house, and the overall pressure differential is choked off at both ends, stopping the chimney effect entirely.[3]

A house operates as a dynamic pressure system, not just a collection of isolated rooms separated by drywall. The next time a cold draft sweeps across the baseboards, recognize that the air is not merely blowing in from the outside—it is being actively pulled in by the warm air escaping through the roof. Fixing the freezing floor in the living room requires stopping the invisible leak in the attic, proving that the most effective weatherproofing always starts with building science.[1][3][4]