Air Infiltration & Leakage (Part 1)

portrait photo of Michael

Michael W. Dickenson, P.E., CFEI, CVFI

Air Infiltration and Leakage – Money Saving Solutions for Homes and Businesses

Although addressing air infiltration and leakage is critical throughout the year, it is especially important to address before winter arrives. In this blog, we will discuss air infiltration and leakage, what they are, and how they can impact energy costs. We will also point out simple steps that home and business owners can take to reduce the excess costs brought on by air infiltration and leakage. 

What Are Air Infiltration and Leakage?

Air infiltration and leakage occur when unfiltered, unconditioned air passes through a structure’s “building envelope” via cracks, damaged seals, or improperly sealed building penetrations.

Specifically, air infiltration refers to the quantity of unconditioned air (typically from the outdoors) entering/seeping into the interior space; where air leakage refers to conditioned air lost/leaking out of the interior space to the outdoors.

When infiltration and leakage occur, the air must pass through the building envelope. The building envelope is the space separating interior, conditioned spaces (such as living rooms and bedrooms in residential construction, or offices and meeting rooms in commercial construction) from outside/unconditioned spaces. 

Why Should Home and Business Owners Care About Air Infiltration and Leakage?

Air infiltration and leakage impact heating, ventilation, and air conditioning (HVAC) system(s) in negative, costly ways because they force HVAC units to have higher-than-average run times. Essentially, the longer an HVAC system runs, the potential for increased wear, coupled with the increased energy used, results in higher costs. Unfortunately, due to the nature of the problem, air infiltration and leakage are not easily recognized and could go unnoticed – and unaddressed. This is problematic in more ways than one.

For home and business owners alike, air infiltration and leakage result in increased energy usage as the HVAC system tries to condition air from the outside.

Where Do Air Infiltration and Leakage Occur?

Common areas where air infiltration or leakage occur are window seals, chimneys, bathroom exhaust fans, and their ductwork, or at wiring penetrations. Due to pressure differences between the conditioned space and the outdoors, it is common for air to infiltrate through cracks within the building envelope on lower levels, basements, and crawlspaces. Conversely, it is common for air leakage to take place with higher levels, including chimneys, upper floors, or at cracks between the attic and conditioned spaces. (Fun fact: the driving force for air infiltrating at lower levels coupled with air leaking at upper levels is a phenomenon known as the stack effect, a discussion for a later blog.)

If buildings/homes have considerable air infiltration or leakage, it can be indicative of a larger issue and trained professionals should be consulted.

How Can Home and Business Owners Lower Energy Costs by Reducing Air Infiltration/Leakage?

Simply put, reducing air infiltration and/or leakage results in reduced energy costs (and potential tax credits or incentives).  Here are some steps home or business owners may take to minimize air infiltration and leakage:

  • Apply foam sealant, as directed, to areas where air movement can be felt. 
  • Examine and replace deteriorated exterior door seals and thresholds.
  • Ensure windows are locked and window seals are intact. (Consult with a professional to replace or repair window seals and parts).
  • Minimize opening/closing exterior doors during extreme winter temperatures.
  • Within the crawlspace/basement, seal gaps around supply-air ductwork and floor connections.
  • Examine bathroom exhaust fans, replacing backdraft dampers, if needed, and sealing gaps/spaces around the exhaust fan housing.

NOTE:  Do not attempt any of the suggested tips with which you are not comfortable. In some cases, a trained, licensed contractor may be required. Safety is paramount when dealing with electrical wiring or other potentially hazardous systems and materials.

In part 2, we will discuss how air infiltration/leakage is measured and what the measurements mean. In addition, we will examine “leaky” vs “air-tight” construction types, as well as estimate cost differences between the construction types.