6.6203.2 Dehumidifying Ventilator Serving Multiple Dwelling Units (All Building Types)

Whole Building Ventilation
Desired Outcome: 
Humidity controlled to achieve optimum indoor air quality ( IAQ IAQ Indoor air quality )
The authority having jurisdiction may require that a licensed professional perform certain tasks outlined in this detail.
For supporting material, see Referenced Standards.
Equipment specification

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

Equipment will be ENERGY STARĀ® qualified (where applicable)

Settings will be maintained through power failure (auto restart)

Dehumidification ventilator will be a ducted unit

Dehumidification ventilator will be able to provide outside air

Efficiently remove humidity

Ensure ease of operation

Provide ventilation with outside air

Ensure appropriate equipment is specified

Ensure design and installation are feasible


System with enough capacity to handle humidity from outside air ventilation and internal gains will be selected

Humidity levels inside the space will be maintained at less than 60%

Note: As outdoor temperature drops, indoor humidity will need to be low enough to prevent condensation in building enclosure

ASHRAE ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers, www.ashrae.org 62.2 and local code requirements should be followed for identifying design airflow rates within apartment dwelling units.

All other areas will follow local code requirements and/or ASHRAE ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers, www.ashrae.org 62.1 requirements

Air flows will be measured in accordance with ANSI ANSI American National Standards Institute, www.ansi.org / ACCA ACCA Air Conditioning Contractors of America, www.acca.org Standard 5 or ANSI ANSI American National Standards Institute, www.ansi.org / ASHRAE ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers, www.ashrae.org Standard 111 and adjusted to meet design requirements

Efficiently remove humidity

Provide sufficient outdoor air to desired locations

Avoid moisture problems associated with over ventilation in a hot and humid climate


Equipment will be located in an area with access to heating, ventilation, and air conditioning supply trunk line or plenum, outside air

Fans, service switch Service switch An electrical switch that controls the complete flow of electricity to a mechanical device , filters, drain, and drain pan will be accessible for maintenance or replacement

Easily maintain equipment

Maintain designed air flows and system performance

Ensure occupant health and safety


Installation will be in accordance with manufacturer specifications and local codes

Dehumidifying ventilator will be mounted securely in accordance with manufacturer specifications and local code

Requirements (in terms of seismic restraints)

Dehumidifying ventilator will be oriented so the equivalent length of the duct run is as short as possible

Dehumidifying ventilator will be isolated from the building framing unless specifically designed to be directly attached

Maintain manufacturer warranty and proper installation

Ensure short duct runs achieve optimum air flows

Ensure dehumidifying ventilator is mounted securely

Ensure dehumidifying ventilator housing or building framing does not shake, rattle, or hum when operating

Minimize noise


Operation of the dehumidifier will be based upon humidity/temperature in the return air, or provide supply air at a specified temperature and humidity

Ensure system operation controls the humidity


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

Condensate drain

Condensation shall be drained to a location approved by the local jurisdiction

Prevent moisture problems

New connecting ductwork

All exposed ductwork outside of the building will be insulated to a minimum R-12, protected from weather exposure and sealed at all penetrations into building shell

All ductwork outside of conditioned space will be insulated to a minimum of R-8

Ensure durability and energy efficiency of ductwork

Distribution systems

Note: Dehumidifying ventilator provides the outdoor air supply fan

The rest of the ventilation system will be installed in accordance with SWS 6.6104.1 Outdoor Supply Air Handling Unit Serving Multiple Dwelling Units or Corridors (All Three Building Types)

Achieve the desired air flows to and from the desired locations

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


Verification of the dehumidification unit and controls will be performed and documented

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

Property manager education

Property manager will be educated on purpose of system, and how and when to change filter and clean drain pan, if applicable, in accordance with manufacturer specifications

Ensure occupant health and safety

Preserve integrity of system