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Ductwork


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Ductwork Contents:

CSI NUMBERS
DEFINITION
CONSIDERATIONS
COMMERCIAL STATUS
IMPLEMENTATION ISSUES
GUIDELINES

RESOURCES

CSI Numbers:


DEFINITION:

A high quality duct system greatly minimize energy loss from ductwork. Leaks in ductwork can contribute 20 to 60 percent of the air leakage in a house. The system should be airtight, sized and designed to deliver the correct air flow to each room. MADAIR (Mechanical Air Distribution And Interacting Relationships) refers to the principles underlying duct installations.


CONSIDERATIONS:

Duct leakage is a major source of energy loss in homes and a contributor to poor indoor air quality. Good system design, improved duct and sealing materials combined with proper installation reduce energy losses. Some design strategies are simple, such as allowing adequate airspace under interior doors to permit air to return to plenums outside of the room.

Depressurization and overpressurization can occur in homes due to faulty duct system characteristics. As a result, air is exchanged (through infiltration and exfiltration) with outside air and hotter attic air.

Depressurization can be caused by closing interior doors, blocking air that is supplied to rooms from reaching the return air plenum (usually located in a central area of the house). The return air plenum will consequently be starved for air and pull air from wherever it can. This can include the flue from a gas water heater, which is why some water heaters show signs of flame "rollout" (burn marks on the outside of a gas water heater). In the same scenario, the rooms receiving air from the system are overpressurized. The air can exfiltrate (migrate outdoors) and cause energy losses or enter wall cavities possibly introducing moisture problems.

Poorly sealed duct connections permit attic air to enter the system in cases of depressurization or become energy losses as system air is lost into the attic. Proper techniques, materials, and training to address these problems are available. A growing number of regulatory and energy conservation agencies throughout the nation are actively seeking to eliminate poor ductwork systems as a serious health, safety, and energy issue.

Commercial
Status
Implementation
Issues
technology suppliers cost financing public regulatory
High Quality Duct System
Legend
green Satisfactory
yellow Satisfactory in most conditions
red Satisfactory in Limited Conditions
black Unsatisfactory or Difficult

COMMERCIAL STATUS

TECHNOLOGY:

Well documented but not well distributed.

SUPPLIERS:

Limited.

COST:

5% to 10% higher than conventional installations.


IMPLEMENTATION ISSUES

FINANCING:

Available.

PUBLIC ACCEPTANCE:

The public is generally not aware of the role ductwork plays in energy use or air quality.

REGULATORY:

Sections 503.9 and 503.10 of the Model Energy Code address ductwork.


GUIDELINES

  • 1.0 Duct System Design Elements
  • Overall system design should include the following elements:

  • 2.0 Airflow Factors
  • 3.0 Sealing the Duct System
  • 4.0 The City of Austin ECSD provides MADAIR site tests.
  • See Resources.

    RESOURCES


    PROFESSIONAL ASSISTANCE



    COMPONENTS / MATERIALS / SYSTEMS



    GENERAL ASSISTANCE:

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    This document was adapted to HTML by Bill Christensen, sysop and environmental editor of Texas InfiNet, an online community for progressive information.

    Sustainable Building Sourcebook web version copyright Sustainable Sources 1994-1999.