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Stack Effect

The stack effect is a force that affects the conditions inside your home. It’s important that you come to grips with it.

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Much like gravity, the stack effect is invisible, yet its effects are real. You may not see the air coming in or leaking out of your home. But you’ll experience first-hand its effects. Temperature fluctuations, condensation, mold spores, and clammy indoors are all by-products of the stack effect, which brings in moisture-laden and moldy outside air.  

Still can’t wrap your head around this concept? Here, we will shed more light on the stack effect so you can know what to expect and how to mitigate it. 

stack effect illustration

How the Stack Effect Happens 

Warm air usually rises whenever there’s less cool air in a home. As this air goes up, it creates negative pressure at the base of your home. So, you now have a scenario where warm, light air keeps rising and exiting your home, and cool air rushing into the lower part of your home and pushing up the warm, light air. For every cubic foot of warm air that goes out, another cubic foot of cool air comes in to replace it. How much the house leaks depends on the temperature difference between the upper and lower parts of your home. 

What Triggers the Stack Effect? 

Unless these two conditions exist, the stack effect won’t occur in your home. 

Upward moving air: Warm air has to go up and create room for cool air that comes in to replace it. Usually, the warm air stays on top while the cold air sinks to the bottom because one is denser than the other. 

Air entrance and exit: There must be an entry and exit point for air in your home. The air will get in through the low-lying entrances like foundation cracks and rim joist/band board and exit from gaps or places like the attic. 

Seasonal changes will determine how much stack effect you’re going to experience. If the weather is warm, temperatures will rise, and more air will exit your home. This changes during winter.  

How Does the Stack Effect Affect You? 

Leave the entryways and exits in your home open long enough and you’ll experience the many undesirable impacts of the stack effect, which include:  

  • Respiratory problems: Mold spores, dust, and other particles will float into your home and cause allergic reactions and breathing problems like asthma. Persistent coughs and runny nose are signs of unclean air. 
  • Mold/mildew growth: Upward moving air that sweeps through the crawl space will bring up with it mold spores. If moisture is present, these microorganisms will multiply fast and take over your crawl space.  
  • Higher heating and cooling costs: Fluctuating temperatures, muggy air, and persistent moisture will force you to run your HVAC for several hours each day to create a favorable internal environment. Not only does will this overwork your unit, but it also drives up your energy costs. Your bills may go up 25%.  
  • Water damage:  With time, the moisture that you’ve been ignoring will start damaging your walls and wood. Flooding can also happen if the crawl space lies in the path of water. 
  • Crawl space repairs: Water damage, wood decay, and wall cracks are all problems that will necessitate professional repairs.
  • Damages your HVAC: Cold air that gets into your home through the crawl space in the winter turns your HVAC into a workhorse. It will work harder and wear out faster. This will mean frequent repairs. 
  • Condensation: You can also expect condensation to increase in the crawl space. In fact, for every degree that the air cools, relative humidity goes up by 3%. This is bad news for anyone struggling to control crawl space moisture. 

It’s possible to overcome the stack effect and create a comfortable, dry, mold-free home. The best way to do that is to regulate airflow from the outside. 

When you’re dealing with a sneaky issue like the stack effect, it’s good to involve a professional who understands its effects and how to mitigate them. Tar Heel Basement Systems can help you seal your crawl space to stop outside air from infiltrating your home. To get started, schedule a free crawl space repair inspection.

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Winston-Salem, NC 27103


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Fuquay-Varina, NC 27526