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Stack Effect

Stack effect is the movement of air in and out of a building. The air at the bottom (the hottest air) is pushed upward before being forced out of the home. The stack effect increases when the air outside is colder than the air inside.

What Is the Stack Effect?  

Stack effect graphic

Air comes in and exits your home continuously through the stack effect, which boils down to the exchange of air. This movement of air creates a vacuum that pulls outside air inside the crawl space or basement and up into your home. Warm air rises through your home and escapes via open windows, gaps in the ceiling, the attic, recessed lights, or ventilation openings. The upward moving air eases the pressure at the bottom of your home and as a result, cold air sneaks in through open windows, doors, or other openings.   

In cold weather, the stack effect causes heat to go up together with the warm air. But it’s much weaker due to cooler temperatures. When a cubic of warm air floats up and out, a similar volume of cold air flows in to replace it. The temperature difference between the lower and upper parts of your home will determine the extent of air leaks.  

What’s Behind The Stack Effect? 

The stack effect happens only when the following conditions exist in a home or building:  

Entry & Exit Point:

Air comes into the ground-level entrance and leaves via exit points. Both must be present for the stack effect to occur.  

Rising Warm Air:

The other pre-condition is upward moving warm air, which goes up and creates a vacuum for cold air.  Warm air is usually lighter and will go up while cold air is heavier and will settle at the bottom.  

Let’s say you have crawl space vents. The air in your crawl space might be warmer or cooler than the surrounding air. If the air is cool, it will settle at the base. But, once temperatures start rising, the air will warm up and rise through the living space before exiting the attic. 

How the Stack Effect Affects You  

The stack effect does more than make indoor air conditioning uncontrollable. It will also investigate the following issues:  

Health Problems:

Your biggest concern is the fact that the stack effect brings with it allergens, insect droppings, and dust, which can all cause allergic reactions when they get into your living space. The severity of symptoms can range from mild signs like a runny nose and coughs to severe breathing problems.  

Mold & Mildew Infestation:

As the cold air sweeps into the crawl space and goes up your home, it brings with it tiny mold spores. These microorganisms are small enough to float in the air. That means they’ll spread around your home and even attach to your damp walls, where they will grow quickly.  

While both microorganisms thrive in extremely humid conditions, you’re likely to see them grow if the crawl space remains open.  

High Utility Costs:

An open crawl space will drive up your energy costs by 15-25%. Unregulated airflow means you’re going to experience swinging temperatures and moisture buildup, which will force you to use your HVAC or dehumidifier. Come winter, you will find that your home is colder than usual. In the summer, it will be too hot. Both will again require excessive air conditioning.  

Unnecessary Repairs:

Open crawl space vents are more than a nuisance. They allow moisture-laden air to get in and cause wood rot, which could leave you with structural problems that will compromise your home’s safety.  

Not only does the stack effect impact your home negatively, but it can also have a detrimental effect on your home’s efficiency and the health of your loved ones. You can resolve this issue with the help of a crawl space professional.  

Installing vent covers and encapsulating the crawl space with a 20-mil plastic vapor barrier can help prevent air exchange and all the undesirable effects of cold outside air. If you’d like to seal up your crawl space, schedule a free crawl space inspection and repair quote with Groundworks today. 

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