What is Stack Effect and How it Impacts Energy Efficiency?

Stack effect is also known as chimney effect. It is a phenomenon that essentially occurs due to temperature and pressure differences. Most HVAC contractors know about it, but non-specialists usually don’t. Hot air is lower in density as compared to cold air. This is why hot air rises up towards the ceiling or upper stories of a house. When it does, it leaves behind a vacuum with low pressure in the lower areas, such as the ground floor.

The low pressure causes the cold air through cracks, holes, windows and basement openings to rush in and fill the vacuum. The HVAC system then warms up this cold air which, in turn, rises up once again and escapes through the openings in the upper areas of the house. A vacuum is again created and a fresh supply of cold air is pulled in to fill the space.

This is a cycle that can continue for good due to stack effect. As long as the cycle continues, you can’t effectively regulate the temperature inside a building. This is simply because the cyclical movement of warm and cold air will continue to happen due to the stack effect.

Stack effect can be made worse by a number of factors. It also has a direct impact on the energy efficiency of a building. Here is a look at these aspects of the stack effect and tips on how to prevent the effect from disturbing the temperature regulation of your home.

Factors That Contribute to Stack Effect

Building Height: The higher a building is, the more pronounced is the stack effect. This is because a greater difference of pressure then exists between the bottom and top of the building. This greater difference encourages the movement of hot and cold air, creating a cycle which prevents the building from being properly cooled in the summers and heated in the winters.

Moisture: Moisture increases air density. When a furnace treats cold air, it effectively removes the moisture to achieve the degree of warmth that we desire in the winters. However, warming up moist air also means that the difference in the density of the cold and hot air is more significant. This temperature difference can exacerbate the stack effect.

Indoor/Outdoor Difference: There is a natural difference in the indoor environment of a building and its outdoor environment. Various methods, such as ventilators, are used to regulate this difference and control the airflow into the building and out of it. When this difference is not properly regulated, the difference between the temperature and pressure of the indoor and outdoor environments can give rise to the stack effect. The greater is this difference, the greater will be the stack effect.

Issues Caused by Stack Effect

Stack effect can create a number of problems when it comes to temperature and air pressure regulation of a building. These include:

  • Poor Energy Efficiency: Due to stack effect, the HVAC system of a building is unable to perform efficiently. The effect causes loss of heat in the winters and cool air in the summers. So the HVAC has to exert more and more without delivering the desired results. This causes higher energy bills, a higher risk of HVAC malfunction, and poor temperature regulation.
  • Air Movement: Most buildings and homeowners do not want air movement in the indoors. Such movement can result in doors that slam often and hallways and corridors which feel draughty. The stack effect results in a continuous air movement from the lower portion of a building to its upper areas. This creates a windy feeling in many sections of the building.
  • Air Moisture: The continuous movement of cold air into the building brings excess moisture. This can promote perennially moist conditions in certain sections of a building, leading to the growth of mold, mildew and bacteria.

The Solution

It is possible to mitigate stack effect through insulation and air sealing. For this, you will first need to conduct a thorough inspection of the HVAC air ducts as well as the overall structure of a building. It is typically advisable that you hire a professional contractor for the job. A professional will identify the leaks, cracks, holes and openings that promote air leaks and cause the stack effect.

Hiring a Greenville Heating and Air Expert

If you experience air draughts, poor HVAC heating or cooling, hot and cold spots, and other problems that indicate air leaks, we can help you. Here at General Air, we have been offering comprehensive HVAC services to Greenville homeowners and families for many years. Call us today to schedule an inspection or get an estimate for an HVAC job.

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