The Stack Effect

The stack effect — do you know what it is? Most of us understand the concept of convection: under the influence of gravity, hotter and less dense air rises, and colder, denser air to sinks. When you apply this concept to your home, it is called the “stack effect,” and it can have a noticeable impact on your home’s heating and cooling bills.

Allow us to explain:

Through the process of convection, air, which has been warmed by your heating system, will rise to the uppermost regions of your home. This doesn’t end when the warm air reaches the ceiling of the top floor as gaps, cracks and voids created by recessed lighting, electrical outlets, etc., provide a passageway for warm air to escape into the attic.

This escaping air creates negative pressure inside your home, which creates a vacuum that draws cooler air into the lower floors, creating an endless cycle of heat transfer, known as, you guessed it — the stack effect.

Symptoms of the Stack Effect include cold drafts near exterior walls (around electrical outlets and window trim) and in the basement. You may also notice that the floors above your basement are excessively cold. Another telltale sign of the stack effect is discoloration of the fiberglass insulation installed in the attic floor. This is caused by dust particles left behind by escaping air.

Because your home is constantly losing hot air, your heating system has to work overtime to maintain a constant temperature, which can make your heating bills unnecessarily high.

During the summer when indoor air is cooled, the stack effect will occur in reverse: the top floors of your home will have a lower air pressure relative to the outdoors, creating warm air infiltration in upper portions of the house, causing cool air to exit through the bottom of your home. Although not as pronounced as it is in the winter months due to the lower indoor/outdoor temperature differences, the reverse stack effect can still have an impact on your cooling bills.

Making sure your home is properly sealed and having an HVAC system designed specifically for your home are the two greatest ways to avoid losing hard earned dollars to the stack effect.

The stack effect illustration

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