What Is the Stack Effect Pressure?

Before delving into the reasons for the stack effect or the ways in which it can impact you, there’s a simple question to ask first. What is the stack effect in the first place? Here’s a brief primer on what the stack effect is and how it might impact you.

stack effect

Entrances and Exits

The first thing the stack effect needs is an entrance and an exit. The stack effect happens where there’s an entrance for air in the crawl space or basement and an exit for air in the attic. Almost all attics have an exit for air of some kind, even if it takes a bit of time for it to go through the pathway. That means the problem usually rests with crawl space vents.

When you have an entrance and an exit for air, you’re usually going to end up with the stack effect. This can even be a problem in one-story homes, where the air doesn’t have to travel very much. These entrances and exits are an important part of the stack effect and removing them typically helps.

Warm Air Rises

The second important thing that drives the stack effect is the fact that warm air rises and cool air sinks. This is true regardless of the temperatures of the air; it will automatically rearrange itself so that the warmest air goes to the top and the coolest air goes to the bottom. If the cool air is on top of the warm air, the warm air will move upward through space.

When air enters the crawl space through crawl space vents, it’s either going to be cooler than the surrounding air or warmer than the surrounding air, depending on the weather. If it’s cooler, it will stay in the crawl space for some time, then warm up, rising through the living area and exiting through the attic. If it’s warmer, it will start to rise through the living area as soon as it enters the home.

Tiny Airborne Particles

What’s the big deal with the stack effect? Aside from the fact that it brings in air from the outside, which might include all manner of things, it’s important to note that it’s not just air that’s coming up through the home. The air might include tiny airborne particles it picked up from whatever’s happening in your home’s crawl space.

Many types of particles can become airborne. Mold spores, dirt, dust mites, pest droppings, and many other types of particles are small enough for the air to pick them up. When that air sweeps through your home, those airborne particles are also sweeping through your home, spreading them across your living space. More than 50 percent of the air you’re breathing in your home comes from the crawl space, so whatever is in this area under your house also is in the air circulating throughout the rest of your home and affecting you.

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