It’s your furnace’s job to fill your home with warm air, but the rest of your home must do its part to keep that air inside -- otherwise you’re just paying to heat the great outdoors. And when it comes to meeting this challenge, multi-story homes may get a little trouble from the “stack effect.”

What is the Stack Effect?

The stack effect is a major challenge for skyscrapers, but it can also be a factor for two-story family homes. It’s a condition in which the structure acts like a giant chimney, efficiently funneling warm air upwards until it eventually leaves the structure entirely.

The stack effect occurs when the outside temperature is substantially lower than the indoor temperature. Cold air is denser than warm air, so when cold air enters the structure at the bottom, it pushes warm air higher. This creates an airflow that actually pulls in more cold air and intensifies drafts. The taller the structure, the stronger the airflow.

This is why revolving doors were developed shortly after the first skyscrapers. The force of the suction at ground level was so strong in the winter that people would struggle to pull the doors open!

Why is this a Problem?

The obvious problem is that you’re losing treated air, and therefore are wasting energy and running up your heating bill. But another factor is that this problem can become worse over time.

If the airflow is especially strong, that puts pressure on fine cracks, crumbling masonry, cracking weather stripping and other vulnerable areas where drafts are just barely getting through. With sustained pressure, these gaps can widen and expand, intensifying the airflow and accelerating energy loss.

What Can You Do?

In a word: insulate. The stack effect works because warm air has somewhere to go when it reaches the highest level of your home. In many cases, it escapes into the attic through cracked ceilings, leaky air ducts, recessed light fixtures or simply through insufficient insulation on the attic floor. Once it reaches the attic, it reaches the outdoors through any little vulnerability it can find.

While you should seal drafts and maintain insulation all over your home, the barrier between your top floor and the attic is the most important layer for fighting the stack effect. If you think your insulation has degraded or there are air leaks you can’t locate, contact a climate control specialist for help. A trained tech can assess your insulation, locate problem areas and present solutions to seal the top of your home envelope once and for all.

If you’re ready to take the first step, or if you have any other home HVAC needs, reach out to your licensed, local technicians without delay.

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