6.6104.2 Outdoor Intake to Forced Air System—One System per Dwelling (All Building Types)

Supply Ventilation Systems
Desired Outcome: 
Intake reduces pollutant entry, is easily maintained, has proper flow, and enhances building durability
The authority having jurisdiction may require that a licensed professional perform certain tasks outlined in this detail.
For supporting material, see Referenced Standards.
Forced air system

Specifications will be field verified as appropriate to site conditions by installer

Forced air system will be appropriately sized to handle latent and sensible loads of dwelling unit with the addition of conditioned or unconditioned outside ventilation air

The manufacturer's temperature rise shall be maintained

Forced air system duct leakage will be less than 10% of the air handler design flow when measured at 25 pascals

Reduce migration of pollutants from unconditioned spaces


Wiring will be installed by a licensed contractor

Wiring will be installed in accordance with original equipment manufacturer specifications, and local and national electrical and mechanical codes

Refer to NFPA NFPA National Fire Protection Association, www.nfpa.org 70: National Electrical Code for installation requirements.

Prevent an electrical hazard

Intake location

Intake will be installed in accordance with all applicable code requirements and/or the most current version of ASHRAE ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers, www.ashrae.org 62.2

Ensure occupant health and safety

Prevent entry of contaminants

Ensure unrestricted air flow

Mounting intake duct

Outdoor air ventilation duct will be attached as close to the return side of the heating, ventilation, and air conditioning ( HVAC HVAC Heating, ventilation, and air conditioning ) system's circulating fan as possible while remaining in compliance with manufacturer temperature rise specifications

Filtration of ventilation air will be provided before reaching the HVAC HVAC Heating, ventilation, and air conditioning fan

Duct will be connected to intake fitting

Connection and seal will be performed in accordance with supply duct detail

Ensure short duct run to achieve optimum air flow

Preserve integrity of the duct system and building envelope Envelope The separation between the interior and exterior environments of a building that includes a combination of air and thermal barrier


All duct components from outdoor intake to the air handler cabinet will be insulated to minimum R-8

Minimize energy loss

Prevent condensation


Motorized damper and service switch Service switch An electrical switch that controls the complete flow of electricity to a mechanical device will be accessible for maintenance

Ensure accessibility for maintenance

Motorized damper

A motorized damper or equivalent technology will be installed between the outdoor air intake fitting and the return side of the air handler circulating fan

Outdoor air flow will be provided by scheduled operation of the damper or equivalent technology

Damper will be open only when the air handler fan is operating

Prevent air flow when none is desired


Outdoor air intake flow rates will be measured and documented to meet design requirements

Proper operation and calibration of controls and damper sequencing will be verified by installer

Ensure the performance of the ventilation system

Ensure occupant health and safety

Fire dampers

Fire dampers must be accessible for inspection and/or testing by the local authorities; if fire dampers are not accessible from a grill or register, an access door in the ductwork is required

Sealing activities will not interfere with the operation of fire dampers, balancing dampers, or backdraft dampers

Type B fire dampers will be used as required by fire code

Ensure access to fire dampers for safe operation

Minimize static pressure

Maximize air flow

Occupant/property manager education

Occupant/property manager will be educated on the purpose of the system and how it works

Ensure the system is not unintentionally disabled