The Stack Effect: What It Is & How It Impacts Your Home
Did you know nearly 50% of the air you breathe inside your home comes from the crawl space beneath your house? This is because of a natural airflow phenomenon known as the stack effect, which significantly impacts your living environment.
The airflow in and around your home can make a big difference in the air quality and maintenance of the desired temperature. The better you control that airflow, the lower your utility costs and the higher the quality of air inside your home.
In this article, we explain the stack effect, how it impacts your home, and what you can do to minimize its adverse effects.
What Is the Stack Effect?
The stack effect is the natural vertical airflow in a home. As we explained in our glossary page and the illustration above, the stack effect happens when outside air enters the home, usually through vents, moving upwards and exiting from the top.
This process is also what makes a fireplace function by drawing air in to fuel the fire and venting it through the chimney. That’s why the stack effect is known as the “chimney effect.” Unfortunately, the stack effect also generates several undesirable issues, including:
HVAC Strain and Higher Energy Bills
Air losses or additional load due to stack-effect ventilation increase energy and maintenance costs and decrease occupant comfort. For example, cold winter air enters your home’s crawl space or basement through cracks and open vents. As the air warms, it rises into the rest of the house and escapes through cracks in the walls and attic. Any heat escaping causes increased work for the furnace and higher utility bills.
Similarly, hot summer air enters the crawl space or basement, cooling down. As the cool air warms, it rises through the rest of the house, escaping through cracks in the walls and the attic. This causes the air conditioner to work harder to cool the air, increasing utility bills.
Spreading Unhealthy Airborne Particles
The stack effect carries airborne particles, like allergens and mold, from the crawl space or basement into the upper living areas. Warm air introduced into the crawl space raises the humidity, resulting in condensation that drives mold and mildew growth.
When warm air rises through your house, airborne mold spores, dust, musty odors, and other contaminants follow. This decreases indoor air quality and can worsen health issues like asthma and allergies.
Accelerated Fire Spread
In the context of fire safety, the stack effect accelerates the vertical spread of smoke, toxic gases, and heat through a structure. This rapid upward movement compromises multiple floors, potentially trapping occupants and complicating evacuation efforts. The stack effect also intensifies fires by providing a continuous supply of fresh air, fueling combustion, and potentially leading to flashover conditions more rapidly.
In tall buildings, this effect is particularly pronounced, making proper compartmentalization, fire-resistant materials, and well-designed smoke management systems crucial for mitigating the risks associated with vertical fire spread. Understanding and accounting for the stack effect is therefore essential in fire safety planning, building design, and the implementation of effective fire suppression strategies.
Stack Effect Airflow Changes
Several variables drive the stack effect’s overall airflow. They include the outdoor temperature versus the indoor temperature. Another key variable is the size of the openings at the bottom and top of the home, which allows for stack effect ventilation, as well as the height of the home.
As an example, a typical two-story house is 20 feet tall, with nine-foot ceilings. With an indoor temperature of 75°F, an outdoor temperature of 60°F, and openings in the house from cracks and other items at two square feet, the stack effect airflow will be 467 cubic feet per minute (CFM). In that same home, if the outside temperature drops to 30°F, the airflow jumps to 810 CFM. On the other end of the scale, if the outdoor temperature rises to 100°F, the airflow hits 590 CFM.
The impact of the size of the openings due to cracks and vents can also be seen in these calculations. In the same house with an indoor temperature of 75°F, an outdoor temperature of 40°F, and an opening of two square feet, the stack effect airflow is 714 CFM. If the opening increases to four square feet, the airflow increases to 1,428 CFM. Should the opening decrease to one square foot, the flow rate drops to 357 CFM.
As you can imagine, tall office buildings have an enormous stack effect at work. In fact, the early builders of skyscrapers had to invent the revolving door since the stack effect airflow pressure prevented opening ground floor doors.
How To Reduce the Stack Effect in Your Home
There are several things you can do to reduce the adverse effects of the stack effect in your home. A major one is reducing the number and size of airflow openings throughout your home. As the example demonstrated above, cut the opening in half, and the airflow drops by half. Here are several other options.
- Seal wall cracks and openings, including around windows and even wall outlets.
- Add attic insulation and consider replacing compressed or damaged attic insulation.
- Install crawl space insulation and consider encapsulation.
- Add basement insulation, repair cracks, and add necessary waterproofing before installing insulation.
- Install a dehumidifier in your crawl space or basement to reduce moisture and prevent mold and mildew growth.
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Check out our guide, “Everything You Need to Know About Crawl Space Encapsulation” for more information!
Trust Groundworks to Improve Your Home’s Health
The stack effect doesn’t have to compromise your home’s safety or your family’s health. Protect what matters most with professionally installed and customized solutions tailored to your needs.
Trust Groundworks with your crawl space encapsulation or basement waterproofing to stop the stack effect at its source. We’ve helped millions of homeowners throughout the U.S. and Canada create safer and healthier homes. Let us help you, too.
Contact us today to schedule a free inspection and obtain a no-obligation repair estimate!
Stack Effect FAQs
Yes, by drawing in cold air at lower levels, it can increase the risk of pipe freezing. Proper insulation, maintaining adequate heat, and sealing air leaks can help prevent this issue.
The stack effect can create noticeable drafts, especially near doors, windows, and other openings. Weatherstripping, proper sealing, and maintaining consistent indoor temperatures can help reduce these drafts.
Climates with greater temperature differences between indoors and outdoors (like cold winters or hot summers) tend to create stronger stack effects.
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