Stack Effect

I just read “Pressurization Control in Large Commercial Buildings” (February 2010, and have a question for the author: Is there a number of floors in a high-rise office building at which stack effect becomes more prevalent, or can it happen in any high-rise, short or tall? I have a 14-story office building and experience high positive pressure during summer and extreme negative pressure during winter. The building is around 250,000 sq ft, was built in 1984, and is 85-percent occupied, with a large call center (1,100 employees) inside. We have three 125-hp fans in a rooftop fan room and a lot of outside-air, return-air, and relief dampers, but no relief or return fans.
J. Mark Adkins, SMA
iON Management
Dallas, Texas

Author's response:

Generally, the taller the building, the greater the stack effect. Your 14-story building certainly could be experiencing stack effect. Noticing the seasonal variation in building pressure, as you've done, is a start in identifying the reason for the pressure swings. It also would be good to know if those pressures are experienced on all floors or just the top and bottom ones. How does the pressure vary when the fans are turned off?

HVAC-system arrangement and performance can influence building pressurization, as can other building elements, such as door and window seals, shaft arrangements (stairwells, elevators, mechanical), roof penetrations, and lobby vestibules. It's worth looking at the building elements, as well as the HVAC system, to track down the root cause of your pressurization issues. I recommend you take a look at ASHRAE's (the American Society of Heating, Refrigerating and Air-Conditioning Engineers') “HVAC Design Guide for Tall Commercial Buildings” ( It contains information on stack effect.
Dave Moser, PE
Portland Energy Conservation Inc.
Portland, Ore
