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What is an Air Exchange Rate?

A home’s HVAC system not only heats and cools, but a well-designed system also needs to meet a certain air exchange rate so there’s ample fresh air to maintain a comfortable, healthy indoor living environment.

Why Air Exchange Rates Matter

Homes today are tightly constructed and weatherized to limit energy losses. With our long cooling season here in San Antonio, you probably keep your home closed up for extended periods so conditioned air stays inside. If your well-sealed, air conditioned home doesn’t have adequate air exchange, pollutants and allergens are going to stay trapped inside too, and the poor air quality that results can adversely affect your family’s health and well-being.

Air Exchange Rates Explained

An air exchange rate is simply the number of times that air enters and exits different rooms in your home on an hourly basis, or the “air changes per hour.” The standards for residential air exchange rates are established by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE), and the recommended rates vary depending on a room’s use. A bedroom, for example, should have five to six air changes per hour, while a kitchen requires seven to eight.

To ensure that airflow to each room in a home is sufficient, an HVAC contractor will multiply the recommended number of air changes by the room’s volume, divided by 60 to arrive at the needed cubic feet per minute (CFM) of airflow.

In older homes, some fresh air is introduced through air leaks in the exterior shell. However, if you have a tightly-built home, your contractor may advise you that additional measures are needed to ensure ample air exchange and maintain healthy air quality, such as:

  • Installing a ventilation system to introduce a controlled amount of fresh outdoor air.
  • Adding an air cleaner unit to the HVAC system to filter out allergens and pollutants like volatile organic compounds (VOCs).
  • Properly maintaining your HVAC, ventilation and air cleaning equipment and changing filters as needed to keep them working effectively.

If you have concerns about the air quality in your San Antonio-area home and need expert advice, contact us at Beyer Boys.

Our goal is to help educate our customers in the greater San Antonio, Texas area about energy and home comfort issues (specific to HVAC systems).