Air infiltration is not good. Air ventilation is good.
Why? How can air infiltration be located?

Air infiltration is the inadvertent introduction of outdoor air into your home. Infiltration usually occurs through holes and cracks in walls and ceilings. When warm-humid outdoor air contacts an air conditioned environment, condensation can occur and mold can grow. Infiltration pathways are usually include hostile spaces … walls-attics containing a host of allergens. Air infiltration degrades indoor air quality.

Ventilation is the intentional introduction of outdoor air into your home. Incoming fresh air is conditioned before distribution into your home. Fresh air ventilation improves indoor air quality. [I will discuss fresh air ventilation in a future article.]

Building diagnostics identifies air infiltration by locating leaks in the building envelope that allow the entry of outdoor air. We cannot see air infiltration. How do we find the openings that allow it?

Outdoor air is usually hotter or cooler than indoor air … Florida outdoor air is usually hotter. Air infiltration requires an opening in the building envelope … hole, crack. Air infiltration will not occur unless there is a pressure difference to cause air movement. We can “see” air infiltration based upon these three characteristics: temperature differences, envelope openings, and pressure differences. Techniques for locating air infiltration include …

Infrared Camera. An infrared (IR) camera is a device that creates an image based upon temperature differences. The IR camera sees warm outdoor air infiltrating indoors as a contrast between the outdoor and indoor temperatures. If the outdoor and indoor temperatures are the same, the IR camera detects no difference and cannot see infiltration … so the IR camera works on most days, but not all days.

A pressure difference between the outdoors and indoors must exist for air to move from the outdoors into the indoors. This pressure difference is in some cases caused by operation of the air handler. In such case, simply operating the air handler causes air infiltration can then be revealed to the IR camera.

Air infiltration can also be induced by forcing a pressure difference across the building envelope using a blower door. A blower door is a calibrated fan that is usually mounted in a doorway. The fan forces a pressure difference across the building envelope inducing air infiltration through holes and cracks. The IR camera can then readily identify air infiltration.

Ultrasound. Ultrasound is very high frequency sound … beyond human hearing. The sound wave is small and can penetrate cracks and holes that are not readily seen with the naked eye. Temperature and pressure differences are not necessary for ultrasound to reveal a crack or opening.

An ultrasound generator is used with an ultrasound meter. The generator emits constantly warbling ultrasound. An ultrasound meter can detect this emissions.

The ultrasound generator is placed outdoors and the meter is used indoors. If an envelope opening exists, the ultrasound generator sound waves project through the opening and are detected by the meter. This technique works when there is too little temperature difference for the IR camera to work, or a pressure difference cannot be applied across the envelope to induce air flow.

An example when ultrasound works and an IR camera-blower door do not work, is during construction when the walls-roof are up and windows-doors are flashed, but before drywall. Since there is no air conditioning, there is little outdoor-indoor temperature difference … with no temperature difference, the IR camera is effectively blind. Since the attached garage wall is open and the garage doors are usually not installed at this stage of construction, the envelope is not intact … hence, the blower door cannot induce a pressure difference. Ultrasound reveals holes and cracks without relying upon either temperature difference or air movement.

Air infiltration does not promote a healthy indoor environment. Building diagnostics provides tools for finding and eliminating infiltration … even when you can’t see it!

Building Diagnostics … clear solutions for tough problems

Filed under: Building Diagnostics, Green Homes, Indoor Environment Quality