The Indoor Air Quality fan or IAQ fan or a Whole House Ventilation fan is required to address the mandatory Indoor Air Quality requirements of the California Title 24 energy code. The purpose of this fan is to provide a dedicated and continuous ventilation to the home that helps rid the indoor air of pollutants and hence maintain a healthy air quality.
The Indoor Air Quality requirement can be met through a continuously operating exhaust fan or a balanced ventilation system (such as an ERV or an HRV). This fan is required to meet a minimum airflow, a maximum wattage, a maximum sound rating and also follow certain control requirements. More details on these requirements are given further down in this article. Also, once the project nears completion, the IAQ fan’s airflow is to be tested on site by a third part called a HERS rater.
A simple tool to calculate the minimum required Indoor Air Quality fan cfm
The below Whole House Fan cfm calculator uses the Total Ventilation Rate method from the California Title 24 energy code to calculate the minimum Indoor Air Quality cfm for a home.
Formula to calculate the Indoor Air Quality fan cfm
The minimum airflow required by the Indoor Air Quality fan can be calculated per the below method from the California Title 24 energy code (derived from ASHRAE 62.2).
Total Required Ventilation Rate [ASHRAE 62.2:4.1.1]
The total required ventilation rate shall be calculated using Equation 150.0-B.
Qtot = 0.03Afloor + 7.5(Nbr + 1) (Equation 150.0-B)
where
Qtot = total required ventilation rate, cfm
Afloor = dwelling-unit floor area, ft2
Nbr = number of bedrooms (not to be less than 1)
Exhaust fan or an ERV - which one is needed to meet the IAQ fan requirements?
On most projects an exhaust fan would suffice to address the IAQ airflow requirements. You can use any of the bathroom exhaust fans with the dual purpose of addressing the IAQ requirements as well as the local ventilation requirements of the bathroom. Simply be sure that the bathroom exhaust fan cfm is the minimum of 50 cfm or the minimum calculated iaq cfm, whichever number is larger. This particular bathroom exhaust fan will need to run continuously and also follow the IAQ control requirements listed further below.
A balanced ventilation system is a ventilation system that provides supply as well as exhaust air to the home and the airflow of these are equal. Thereby the air coming in and the air going out of the home through this system are balanced. Oftentimes they also have a heat recovery component which helps transfer some of the heat from the exhaust onto the supply. Energy Recovery Ventilators (ERVs) or Heat Recovery Ventilators (HRVs) are some of the most common types of balanced ventilation systems used.
Although a balanced ventilation system is not a mandatory IAQ requirement for single family residential projects, on some projects it might be a cost effective upgrade to help your project comply with the California Title 24 energy requirements. Hence in such cases, a Title 24 consultant might add a balanced ventilation system (such as an ERV or HRV) to your Title 24 report after reviewing it with you. Hence please refer to your Title 24 report or discuss with your Title 24 consultant to check if an exhaust fan or an ERV/HRV is required on your project in order to comply with the IAQ requirements. To figure out if your Title 24 calls out an exhaust fan or an ERV, see the “how does the iaq fan look like in the Title 24 report” section of this article.
Please note, on multi-family projects, a balanced ventilation system is now required as a mandatory requirement per the 2022 California Title 24 Energy code. If instead, an exhaust or supply fan is chosen to meet the indoor air quality requirements, the multi-family dwelling unit will also be required to meet minimum air leakage requirements which will be tested on site post construction by a HERS rater via a blower door test.
Control Requirements of the Indoor Air Quality fan
The IAQ fan should be connected to a manual on-off switch that is easily accessible to the occupant of the dwelling unit.
There also needs to be a label next to the switch stating the following text, or equivalent text: “This switch controls the indoor air quality ventilation for the home. Leave the switch in the ‘on’ position at all times unless the outdoor air quality is very poor.”
Sound Rating requirement of the Indoor Air Quality fan
The indoor air quality fan needs to meet a sound rating of 1 sone, at the minimum airflow required per California Title 24.
What does the Indoor Air Quality fan look like on the Title 24 report?
An indoor air quality fan is listed on the last page of the CF1R of your Title 24 report. It would be under a separate table called the Indoor Air Quality (IAQ) Fans. See below a screenshot of how it would look in your Title 24 report.
The column 1, called Dwelling Unit, specifies the dwelling unit which requires the IAQ fan.
The column 2, called Airflow (CFM), specifies the minimum airflow required from your IAQ fan.
The column 3, called Fan Efficacy (W/CFM), specifies the maximum watts per cfm that the IAQ fan can consume.
The column 4, called the IAQ Fan Type, specifies if your IAQ fan needs to be an Exhaust fan or a balanced ventilation system. If this column reads “Balanced” then you need a balanced ventilation system such as an ERV or HRV.
The column 5 further confirms if you need an ERV or HRV. If this is No then the IAQ system need not provide heat recovery.
The column 6 specifies the minimum energy or heat recovery effectiveness required of the IAQ fan. This is measured in SRE or ASRE.
The column 7 specifies if the IAQ system is required to have a Fault Indicator Display. If a balanced ventilation system is specified as the IAQ, then a Fault Indicator Display is often also required.
The column 8 specifies if an on site HERS verification of the IAQ fan is required.
The column 9 specifies if the IAQ fan is new, existing or altered.
Per the example in the screenshot above, a bathroom exhaust fan which is 30 cfm or larger would be sufficient to address the IAQ requirement of the ADU.
When is the IAQ fan requirement not triggered?
All new constructions, ADUs and new dwelling units need to meet the IAQ requirements
Alterations to an existing home do not trigger the IAQ requirement.
Additions where < 1000 SF is being added do not need to meet the IAQ requirements.
JADUs do not need to meet the IAQ requirements.
Difference between a Whole House Ventilation fan and a Whole House Cooling fan
Please note, a Whole House Ventilation fan is different from a Whole House Cooling fan. The Whole House Ventilation fan runs continuously and maintains air quality. While a Whole House Cooling fan, such as a Quite Cool Whole House fan, operates during certain times of the day and cools the home by drawing in cool air from the outside. 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 IAQ 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, it is only a prescriptive requirement. While the Whole House Ventilation requirements are mandatory for all new constructions, ADUs as well as most Additions.
A simple checklist to make sure you address all the IAQ fan requirements on your project
- Read your Title 24 report to check if you trigger the IAQ fan requirement on your project and if so, do need an exhaust fan or a balanced ventilation fan to address the IAQ requirement.
- If your Title 24 report calls for an exhaust fan as IAQ, you can double one or more of your bathroom exhaust fans to also function as an IAQ fan. While if your Title 24 report calls for a balanced ventilation fan as IAQ, you need to install one or more ERVs or HRVs somewhere central in your home. Essentially, the total cfm of the exhaust fans (or ERVs) that are specified as IAQ fans needs to be more than the minimum IAQ airflow requirement mentioned on your Title 24 report.
- On your plan set, make sure you clearly show and label the exhaust fan or ERV as an IAQ fan.
- On the same sheet where you show the IAQ fan on the plans, also add the below notes. Fill in the blanks below with the actual values of the project.
Indoor Air Quality CFM Requirement calculated through the Total Ventilation Rate Method [ASHRAE 62.2:4.1.1].
The total required ventilation rate is calculated using Equation 150.0-B.
Qtot = 0.03Afloor + 7.5(Nbr + 1) = 0.03 * __ + 7.5 * ( __ + 1) = __ cfm
where
Qtot = total required ventilation rate, cfm
Afloor = dwelling-unit floor area, ft2
Nbr = number of bedrooms (not to be less than 1)
The sound rating of the IAQ fan to be a maximum of 1 sone.
The IAQ fan to be controlled by a manual On-Off switch which is to be accessible to the occupant.
The IAQ fan control switch will have a label clearly stating the following text, or equivalent text : “This switch controls the indoor air quality ventilation for the home. Leave the switch in the ‘on’ position at all times unless the outdoor air quality is very poor.”
On nearing the end of construction, also be sure to get in touch with a HERS rater to schedule an on site test of the airflow of your IAQ fan. This is called an IAQ airflow HERS test and can be clubbed along with all the other HERS measures that your project triggers.
Relevant Section pertaining to the IAQ fan requirements from the California Title 24 Energy code
See below the relevant section from the Title 24 energy code with markings in red highlighting the relevant sections.
