Title 24 Continuous Ventilation and IAQ

Title 24 Continuous Ventilation and IAQ

  • Exhaust Ventilation
  • Supply Ventilation
  • Combination Ventilation
  • Intermittent Ventilation
  • Control and Operation

Indoor Air Quality and Mechanical Ventilation in Title 24

As houses have been tightened up over the last several years due to rising energy cost and
the availability of higher performing building materials, normal infiltration and exfiltration
have significantly reduced. This reduce number air changes has increased the effect of contaminants and pollutants introduced through common building materials, cleaners, finishes, packaging, furniture, carpets, clothing, and other products.


The Energy Standards have always assumed adequate indoor air quality would be provided by a combination of infiltration and natural ventilation and that home occupants would open windows as necessary to make up any shortfall in infiltration. However, later on research revealed that actual overall ventilation rates are lower than expected, indoor concentration of chemicals such as formaldehyde are higher than expected, and many occupants do not open windows regularly for ventilation. This resulted in 2013 Standards including mandatory mechanical ventilation intended to improve indoor air quality (IAQ) in homes.


The following are key requirements for Ventilating newly constructed buildings:
1. A whole-building mechanical ventilation system shall be provided. The airflow rate provided by the system shall be confirmed through field verification and diagnostic testing in
accordance with the applicable procedures.

  1. Kitchens and bathrooms shall have local exhaust systems vented to the outdoors.
    3. Clothes dryers shall be vented to the outdoors.


Design consideration for Residential Ventilation System
1. Ventilation air shall come from outdoors and shall not be transferred from adjacent
dwelling units, garages, or crawl spaces.
2. Ventilation system controls shall be labeled, and the homeowner shall be provided
with instructions on how to operate the system.
3. Combustion appliances shall be properly vented, and exhaust systems shall be
designed to prevent back drafting.
4. The walls and openings between the house and the garage shall be sealed.
5. Habitable rooms shall have windows with a ventilation area of at least 4 percent of the
floor area.
6. Mechanical systems including heating and air-conditioning systems that supply air to
habitable spaces shall have MERV 6 filters or better and be designed to
accommodate the system’s air filter media rated pressure drop for the system design
airflow rate.
7. Dedicated air inlets (not exhaust) that are part of the ventilation system design shall
be located away from known contaminants.
8. A carbon monoxide alarm shall be installed in each dwelling unit in accordance with
NFPA Standard 720.
9. Air-moving equipment used to meet the whole-building ventilation requirement and
the local ventilation exhaust requirement shall be rated in terms of airflow and sound:

  1. All continuously operating fans shall be rated at a maximum of 1.0 sone.
    b. Intermittently operated whole-building ventilation fans shall be rated at a
    maximum of 1.0 sone.
    c. Intermittently operated local exhaust fans shall be rated at a maximum of 3.0
    d. Remotely located air-moving equipment (mounted outside habitable spaces)
    need not meet sound requirements if there is at least 4 feet of ductwork between
    the fan and the intake grille.


There are three typical solutions to meeting the Title 24 air ventilation requirement:

  • Exhaust ventilation
  • Supply ventilation
  • Combination of supply and exhaust ventilation. (If the supply and exhaust flows are
    within 10 percent of each other, this is called a “balanced ventilation system.”)

The whole-building ventilation system may operate continuously or intermittently. The wholebuilding ventilation rate is determined for continuous ventilation; if the system is operated intermittently, an adjustment is made.


Ventilation Rate (CFM) for Residential Buildings can also be determined using the following table:


Source: ASHRAE 62.2


(Excerpted from the CEC Title 24 Residential Compliance Manual)




















Exhaust Ventilation

Exhaust ventilation is usually achieved by a quiet ceiling-mounted bath fan or remote mounted inline or exterior-mounted fan. Air is drawn from the house by the exhaust fan, and outdoor air enters the house through infiltration.

Many high-quality bath fans are available in the 30- to 150-cfm size range that are quiet
enough to be used continuously. One or more fans of this size will meet the requirements of
most homes. The exhaust fan can be a dedicated IAQ fan or a typical bath fan that is used
for both whole-building ventilation and local ventilation.

Inline fans (either single pickup or multipoint pickup) can be a very effective method of
providing quiet exhaust ventilation from one or several bathrooms. Inline fans can be located
in the garage, attic, basement, or mechanical room.

Exterior-mounted fans can be mounted on the exterior wall or on the roof. A sound rating is
not required for remote or exterior fans with at least 4 ft. of duct between the closest pickup
grille and the fan.

(Excerpted from the CEC Title 24 Residential Compliance Manual)



Supply Ventilation

Supply ventilation works by bringing outside air into the house through a dedicated supply
fan or the central forced-air system air handler and escapes through exfiltration.

The air handler or supply fans can be located on the exterior of the house or in the garage,
attic, basement, or mechanical room, but the placement of the outdoor air inlet should avoid
areas with contaminants, such as garages, barbeque areas, and chimneys. If a dedicated
fan is used, care must be taken to avoid introducing too much outdoor air into one location
and creating uncomfortable conditions. The ventilation air can be distributed by a dedicated
duct system separate from the central forced air distribution duct system.


Alternatively, the central forced-air system air handler can be configured to function as a
ventilation supply system by installing a dedicated ventilation air duct that connects to the
return plenum of the air handler and to the dwelling exterior. This strategy, called central fan
(CFI) ventilation, uses negative pressure in the return plenum to pull outdoor air in
through the ventilation air duct and into the return plenum, then the central system air
handler distributes the ventilation air through the house. A damper and controls must be
installed that ensure the air handler delivers the required ventilation airflow regardless of the
size of the heating or cooling load.



(Excerpted from the CEC Title 24 Residential Compliance Manual)



Combination Ventilation

Combination systems use both exhaust fans and supply fans. If both fans supply the same
airflow, the system is balanced, and the house has a neutral pressure.

Combination systems are often integrated devices, sometimes with a heat exchanger or
heat recovery wheel. The supply and exhaust airstreams are typically of equal flow.


Combination systems can also be a mixture of supply fans and exhaust fans, such as a
quiet continuous bathroom exhaust fan matched to an outdoor air connection that introduces
air into the return air plenum of a continuously operating central heating/cooling system air

Note: Ventilation systems that constantly operation the central heating/cooling system air
handler can use a very significant amount of electricity annually and are not permitted by the
Energy Standards

(Excerpted from the CEC Title 24 Residential Compliance Manual)


Intermittent Ventilation

In some cases, it may be desirable to design a whole-building ventilation system that
operates intermittently. One common example of intermittent ventilation is when outside air
is ducted to the return plenum of the central heating/cooling system, and thus the central
heating/cooling system fan is used to distribute the ventilation air to the rooms in the

Intermittent mechanical ventilation systems, devices, or controls may be approved for use
for compliance with the HERS field verification requirements for whole-building mechanical
ventilation airflow.

Intermittent ventilation is permitted as long as the ventilation airflow is increased to respond
to the fewer hours of fan operation and the tendency of pollutant concentrations to build up
during off cycles.

(Excerpted from the CEC Title 24 Residential Compliance Manual)


Title 24 Ventilation Control and Operation

Title 24 requires that the ventilation system have an override control that is readily
accessible to the occupants. The control must be capable of being accessed quickly and
easily by the occupants without having to remove panels or doors. It can be a labeled wall
switch by the electrical panel or it may be integrated into a labeled wall-mounted control. It
cannot be buried in the insulation in the attic or the inside the fan. The occupant must be
able to modify the settings or override the system.

If intermittent fans are used, they must be controlled by a timer, and they must have an
increased airflow rate to compensate for the off time.

Time-of-day timers or duty cycle timers can be used to control intermittent whole-building
ventilation. Manual crank timers cannot be used, since the system must operate
automatically without intervention by the occupant. Some controls “look back” over a set time interval to see if the air handler has already operated for heating or cooling before it
turns on the air handler for ventilation only operation.


(Excerpted from the CEC Title 24 Residential Compliance Manual)




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