The airflow rate input for the HVAC system is not valid when modeling a conventional HVAC system. The CEC restricts the airflow rate on conventional systems to a mandatory minimum of 350 cfm/ton of airflow to a maximum of 600 cfm/ton.
At the System level of the building tree, in the HERS tab, edit the airflow setting and set this number to a valid rate.
If you are modeling a Zonally Controlled system, this airflow rate is allowed to go lower than 350 cfm/ton. Zonally Controlled systems are multiple zone systems with dampers designed to independently control different areas of the home. See the Residential Compliance Manual for more information on this type of system.
If your system is Zonally Controlled, in the HERS tab you can check the box for Zonally Controlled and then a lower airflow number will be allowed.
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