Understanding Air Pathways

Air flow is created by pressure differentials.  Air flow always flows from higher relative pressure to lower relative pressure.  Air will flow through any available opening (pathway) in an attempt to equalize pressure.  Pathways include windows, doors, electrical outlets, floor drains, heating and cooling systems, and most importantly air ducts.

Air Pathways within a Home

A forced air system works by creating a difference in pressure between the area where the supply registers are located and the area where the returns are located.  As air moves from supply diffuser to return air grill, it is diverted or obstructed by partitions, creating pathways of air movement throughout the home.

How do Air Pathways affect a Home?

Pathways can change from one minute to the next – Opened windows, an exhaust fan, open/closed doors etc… Unintended pathways need to be acknowledged to have a comprehensive understanding of a homes airflow patterns.

Improving Air Pathways

Air ducts are the pathways for energy efficient homes.  With a couple of simple steps you can improve your air pathways.

• Seal the air ducts to prevent costly, conditioned air flow from being drawn from or escape into unknown, unspecified, or unintended areas of the home.
• Filter the air by changing the furnace or air conditioning air filter.
• Make sure that air ducts are not blocked by interior furnishings that prevent their designed use.
• Have the air ducts cleaned to prevent obstructions in air flow.
• Use bathroom exhaust fans when using the shower to exhaust moisture.
• Use kitchen exhaust fans when cooking to exhaust fumes from cooking.
• Have your HVAC technician inspect exhaust flues when they perform annual HVAC inspections to ensure carbon monoxide is properly exhausted.

Pressurization

Air flow is created by pressure differentials.  Air flow always flows from higher relative pressure to lower relative pressure.  If more air is supplied to a room than exhausted, the excess air leaks out of the space and the room is said to be under Positive Pressure.  If less air is supplied than exhausted, air is pulled into the space and the room is said to be under Negative Pressure.

Positive Pressure

If a home or building has too much positive air pressure, it will allow for conditioned air to escape the home causing costly energy concerns.

Negative Pressure

Negatively pressurized homes allow for unconditioned and unfiltered air to be drawn within the home or building.  Debris will enter through cracks and crevices, opened doors, windows, etc…

What’s the Ideal Air Pressurization?

It is ideal to achieve neutral to slightly positive air pressurization.  Though there is a slight loss of conditioned air, a slightly positive pressured home will provide comfort and prevent outdoor contaminants from entering the home or building.

ASHRAE Standard 62.1 “Ventilation for Acceptable Indoor Air Quality” requires proper ventilation and a slightly positive pressurization of buildings. Maintaining a small positive air pressure, relative to the outdoors, limits the entrance of outdoor moisture and is a very common strategy to prevent mold and mildew formation in a building.

How Can You Monitor or Control Air Pressurization?

Air pressure can be monitored through an energy auditor.  An energy auditor will use of a blower door & smoke test to determine the location of air leaks.  After the test is performed steps can be made to improve air pressurization.