You may have never heard of the “stack effect” before, but it has a huge effect on your home. While you certainly do not have to be an expert on how your home is heated during the winter—that is why you keep HVAC professionals like Aire-Tech around—a bit of knowledge can go a long way toward helping you to understand how your house may be losing heat, how to prevent it and when to call for assistance.
The Stack Effect Explained
From chimneys to windows to crawl spaces, no house is a truly sealed up system. The stack effect occurs when the outdoor temperature is much lower than it is indoors. Since cold air is denser than warm air, cold air pushes the warm air higher when it enters the room from the bottom floor. The warm air then escapes through cracks and other openings. This then creates stronger drafts as more cold air enters the room in the absence of warm air. Outside air can slip through any of these access points and change the internal air temperature and quality. When the house begins to feel too cold, you adjust the thermostat to activate the heater. This leads to the unwanted stack effect.
The simple explanation for the stack effect is that it describes how warm air inside a house rises and cold air moves in to replace it. We all know that heat rises, but the stack refers to the movement of air that’s caused by temperature and pressure differences. Just like a chimney allows warm air to rise up and out, your home could be doing the same thing. Since warmer air is more buoyant, it rises, and the negative pressure left behind then pulls in cool air to replace it. While this works for a chimney, it should not be happening in your home.
As long as the temperature within the home continues to change, this cycle of air will continue. Also, it does not just happen during the winter. In the warmer summer months, you may turn down your thermostat to activate the air conditioner. This creates heavier, colder air that sinks to the bottom of your home looking for a way out. A vacuum in the upper areas of your house will then pull hot air through the attic and windows when the cold air leaves through the crawl space.
What Causes the Stack Effect?
The main thing that drives air movement is pressure. Air pressure depends on the density of the air, which is dictated by its temperature. The hotter the air, the farther the molecules are from each other (less dense), creating less air pressure.
Since air moves from areas of high pressure to areas of low pressure, warm air (less air pressure) will rise and cold air (greater air pressure) will sink. As with the stack effect, the greater the pressure difference, the more powerful the air movement.
There are three main things that affect the stack effect:
- Height of the building
- Temperature/pressure difference between the indoors and outdoors
Consequences of the Stack Effect
If left untreated, the stack effect can make it costly and nearly impossible to regulate the temperature within your home. Your HVAC system has to work harder and your energy bill goes up because you will be continuously messing with your thermostat with nothing to show for it. This can also lead to increased wear & tear on your heating and cooling systems while also costing you extra in energy costs.
The stack effect can lead to health concerns, especially if your crawl space is experiencing moisture related issues such as mold or mildew. As the air from your crawl spaces circulates within your home, it can spread mold and mildew spores. Mold spores can cause fungal infections, especially in those with suppressed immune systems or a history of lung problems.
Check for Signs of the Stack Effect
Symptoms of the Stack Effect at work in your house include cold drafts you can feel near exterior walls (especially around electrical outlets and window trim) and cold drafts in the basement.
Up in the attic, evidence of air leakage and Stack Effect energy loss can often be found on the fiberglass insulation installed over the attic floor. Insulation installed near an air leak will often discolor from the dust deposited on the fine fibers by rising air.
The comfort problems caused by the Stack Effect also cause energy problems. With heated air leaving the house and cold air entering, your heating system has to work longer and harder to maintain comfortable interior temperatures. During cold weather when the Stack Effect is strongest, heated air is constantly escaping, and it is being replaced by an equal volume of cold outside air. Since the cycle continues all day and night, you are going to be spending a lot of money to keep the house warm.
Solution to Combat the Stack Effect
There are several ways to keep the stack effect from ruining your winter. We strongly recommend you schedule duct testing with our team, since air leaks in the ducts, in particular the ducts moving through the attic, are a significant leech on heat in the house. You should take standard steps to winterize your home by caulking the windows and placing weather stripping around doors.
Since your home has been experiencing the stack effect due to small gaps and cracks that allow air in and out, sealing those small nooks and crannies will put you one step closer to preventing the stack effect. Air sealing helps to keep hot air from entering during the summer and from escaping during the colder months.
In order to maximize the benefits of air sealing, it is also important to remember insulation. Installing additional insulation in your home (particularly in the attic) will lessen the heat transferred and work to minimize the adverse effects of the stack effect.
The benefits of air sealing and adding insulation include:
- Greater year-round comfort with no drafts or temperature swings
- Lowered energy bills due to a reduced reliance on your HVAC systems
- Increased HVAC system lifespan since the strain to compensate with heating and cooling will be minimized
If you find you simply cannot stay warm in the house no matter what, the issue may be that the heating system cannot keep up with the stack effect. Call Aire-Tech to examine the heater to see if it needs repairs or if it is too old to keep up with heat loss in the home.
If your system needs repair or inspection before winter, call us on 951-926-1002. You can also visit our Contact page and complete the contact form.