How to calculate the Whole House Ventilation (or Indoor Air Quality) requirement for a home?
Updated: Feb 7
First thing to note here is that this is not the same as a Whole House fan. A whole house fan, for example a Quite Cool whole house fan, is a fan that helps with cooling the space in an energy efficient way. While a Whole house ventilation fan or an IAQ fan helps with the ventilation requirements or in maintaining the Indoor Air Quality of the home as required by the Title 24 energy code.
Often the two get confused but more often than not if the city is getting back with a comment regarding whole house ventilation calculation or whole house ventilation fan, it is the Title 24 ventilation requirement that they are talking about. This is also because a Whole House Cooling Fan is not a mandatory requirement in any zone per the CA energy code. While the Whole House Ventilation requirements are mandatory for all new constructions, ADUs as well as most Additions.
The whole house ventilation requirements can be addressed through bathroom exhaust fans. The same bathroom fans can address the local exhaust requirement and also the IAQ requirements. Another alternative is to use Energy Recovery Ventilators to address the requirement. But this will be determined by the Title 24 analysis and report. Please check the Title 24 report to confirm if the space needs an Energy Recovery Ventilation as opposed to simply bathroom exhaust fans.
The minimum Indoor Air Quality as required by the Title 24 energy code can be calculated via the below formula:
Total Required Ventilation Rate [ASHRAE 62.2:4.1.1] Equation 150.0-B:
Qtot = 0.03 * Floor area + 7.5 (Nbr+1) = 0.03 * + 7.5 ( + 1) = = ~ CFM
Qtot = total required ventilation rate, cfm per Title 24 Energy code
Afloor = dwelling-unit floor area, ft2
Nbr = number of bedrooms (not to be less than 1)
The above is the minimum CFM requirement. It can be addressed by all the bathroom exhaust fans in the home. Hence the sum total of all bathroom exhaust fans needs to be at or above the above number.
The Indoor Air Quality requirements are mentioned on the Title 24 report towards the end in the table labelled as IAQ (Indoor Air Quality). See below a screenshot. If the IAQ Fan Type read Balanced in place of Default, it would mean an ERV or an HRV is required.
The table above mentions the minimum CFM required and the maximum wattage allowed. The minimum CFM for all the IAQ fans should be greater than the value mentioned above. i.e. 46 CFM in the above example and the total wattage should be <0.25 Watts/cfm.
This IAQ CFM can be met through a dedicated exhaust fan or can also be met through the bathroom exhaust fans in the home.
The Panasonic Whisper series is a good brand often used for bathroom exhaust fan (and IAQ) purposes. Perhaps you can consider the same or an equivalent product but please make sure the total cfm of all the IAQ fans meets the value mentioned in the Title 24 report.
IAQ fans are required to be ON at all times. However, they are also required to have a manual over ride switch. This switch needs to be easily accessible to the occupant and there should also be a label next to the switch instructing the occupant to keep ON at all times to maintain air quality. An example of the text is "This Switch controls the indoor air quality ventilation for the home. Leave it on unless the outdoor air quality is very poor".
See below the relevant section from the energy code with markings in red highlighting the relevant sections.