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  • Writer's pictureDarrin Card

A Homebuyers Guide To Air Infiltration and Exfiltration

omebuyers spend hours scouring online websites, attending open houses, and walking through potential homes looking for their dream home. During this experience it's crucial to be mindful of potential underlying issues that can impact their comfort and finances. One such concern is air infiltration and exfiltration, the movement of air into and out of a building. Controlling these airflow patterns is vital for enhancing a home's energy efficiency. In this article, we'll explore the significance of managing air movement, the types and causes of air leaks, and effective prevention and control measures.

The Impact of Air Infiltration and Exfiltration (1)

Pressures on a home from wind velocity and direction, differences in outdoor and indoor temperatures, pressurization of the home, and the efficiency of air management systems can cause air infiltration and exfiltration. Air infiltration is air entering the home from the outdoors, while air exfiltration is the flow of air from inside the home to the exterior. These types of air flow are not controlled by mechanical means and can introduce unwanted conditions in the home. Managing air infiltration and exfiltration is key to improving a building's energy consumption and the occupants health. Air leaks introduce unconditioned air into the space, leading to higher HVAC costs for homeowners. Moreover, these leaks may affect indoor air quality by introducing pollutants and allergens.

Types and Causes of Air Leaks (1)

Typically air can infiltrate or exfiltrate a home in three ways:

1. Diffuse Flow: Occurs when building materials cannot control airflow due to cracks or high permeability. Fibrous insulation or uncoated concrete blocks can be culprits.

2. Orifice Flow: Air follows a linear path between entry and exit points, like through gaps around a window or door framing and the finished material.

3. Channel Flow: The most severe type of air leak. This occurs between distant entry and exit points which causes the air to cool and condense, leading to moisture accumulation.

Understanding Air Pressure and Its Role (1)

Air pressure disparities between the interior and exterior of the home contribute to infiltration and exfiltration. Three main pressure types impact airflow:

1. Wind Pressure: Caused by gusting winds acting on building walls and roofs. The average annual wind pressure in most locations in North America is 10-15mph when averaged out over the course of the year. (Air Barrier Systems In Buildings).

2. Stack Pressure: Resulting from atmospheric pressure differences due to height and temperature variations. Stack pressures in cold climates, like Michigan, can cause infiltration of air at the bottom of the home and exfiltration in the upper floors or attic.

3. Fan Pressure: Mechanical equipment, like HVAC systems, can positively pressurize a building. The National Institute of Standards and Technology reports that the added energy to heat and cool buildings due to infiltration and exfiltration can be up to 42% in heating climates (NISTIR 7238)

Recognizing Visual Signs Of Air Infiltration and Exfiltration (2) (4)

Understanding how air works is the first step of being able to recognize unwanted air exchanges. When air enters a home and equal amount of air will exit the home. We typically have devices in place to handle the removal of air through the home, such as ventilation in attics. Air also moves from high pressure to low pressure, so if you have exfiltration of a home that means the part of the home that is exfiltrating air is at a higher pressure than the exterior of the home.

1. Signs of Infiltration: Infiltration of air is pretty recognizable to many people. If you stand next to a window and hold your hand up and feel a slight breeze, that is most likely air infiltration. You can get infiltration through a chimney, doors, and other penetrations in the home. If you are experiencing frequent static electricity discharges in winter you may have an air infiltration issue also. You can also look for "ghost" tracks next to light colored carpet near outside walls. These will be small black streaks or discolored carpet along the walls. Odors can also be a tell-tail sign of infiltration. If you are getting frequent smells penetrating the envelope of your home you may have areas that need to be sealed.

2. Signs of Exfiltration: Exfiltration of air can be a little harder to recognize. One signs may be black streaks at the seams of vinyl siding as pi

ctured, or in other areas around the exterior of the home such as around penetrations. You may notice black edges of fiberglass insulation batts between the joists in the attic.

3. Testing: Testing can be performed to determine the amount of air leakage that is occurring in a home. This is often referred to as a "Blower Door Test". A certified energy auditor will use a powerful fan that sucks the air out of the house. This lowers the air pressure inside the home, the outside air, which is at a higher pressure, then enters the home through penetrations. The auditor then uses tools such as infrared cameras, smoke pens, and other devices to determine where the penetrations exist. A calibrated fan can measure the amount of air being sucked out of the home which will determine the overall tightness of the home. (5)

How To Prevent and Control Air Infiltration (1)

An effective air barrier system is vital to combat air infiltration and exfiltration. This system includes interconnected materials, sealed joints, and building components to create an airtight enclosure. Focus on these features:

1. Continuity: Properly installed materials working together to prevent air leakage at joints. For example, windows should be insulated and sealed from air penetration using products like weatherstripping, caulking, and air barriers.

2. Structural Support: Components must withstand the pressures, both positive and negative put on it. Tape, fasteners, adhesives, etc must be used to prevent tears, rips, movement, etc that may compromise the integrity of the air barrier system. (3)

3. Air Impermeability: Choose materials with low permeability to air. Most building materials will have a measurement of air impermeability that will be reported in Litres/ second per square meter at 75 Pa pressure.

4. Durability: Ensure materials can perform their function throughout the structure's life.

Being aware of air infiltration and exfiltration is a bonus when assisting clients in finding their ideal homes. Educate them about these air leaks' impact on energy efficiency and indoor air quality. Encourage them to consider prop

erties with well-maintained air barrier systems, enhancing energy savings and comfort. The more knowledge you have when walking through homes the more trust you gain with the clients and they will end up with a efficient and sustainable living space. As always, Card Inspection Services will be there to help you answer any questions you may have.


(1) Energy Education "Air Infiltration and Exfiltration" (online)

(2) Allison A Bailes, Green Building Advisor (2023) "What's the Deal With Exfiltration" (online)

(3) Wagdy Anis, Whole Building Design Guide (2016) "Air Barrier Systems in Buildings" (online)

(4) Smarter House "Signs That You May Have an Air Quality Problem" (online)

(5) "Blower Door Tests" (online)

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