?On Wed, Sep 23, 2020 at 05:01 AM, imranindiana wrote:

my comment was without any appliance/fans. 0.3 ACH stringent standard still means that the leaks in the house will result in a complete air exchange in about 3hrs.

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Understood.? I was just noting the relationship between a range hood and that standard.

Btw, it seems like you're interpreting the standard as if it were an expression of natural airflow in the absence of mechanical ventilation, but that it not at all what the standard is about nor what it measures.? In no way does it imply that "leaks in the house will result in a complete air exchange in about 3hrs." In fact, without any fans, ACH will be zero, whether the house is rated at 0.3 ACH or 30 ACH.? ?

The standard is an expression of the uncontrollable ventilation in an unbalanced system.? It's saying that if your HVAC system inflow and outflow is out of balance such that it resulted in a 50 pascal pressure differential, you'd have an additional 0.3 ACH above ventilation system's?design ACH rate (typically 5-10 ACH)?

In the olden days, most residential HVAC systems were unbalanced by design.? ?The furnace or AC system pumps air from outside to the inside, creating positive internal pressure, and the air exits through open doors and windows and leaks through closed doors and windows and other parts of the building envelope.? When you're heating or cooling the incoming air, you're "losing" the energy invested when you send that air back outside.? ?Such systems also often have much higher ACH rates than is needed to maintain "fresh" air.? An energy efficient system seeks to minimize the ACH down to the level needed to maintain fresh air (5-10 ACH), and to recover the energy of the exiting heated/cooled air and transfer that energy to the incoming air.? ? To do this predictably, you need to minimize the potentially uncontrolled airflow, which is that the standard is about.? ?