5.3003.36 Ductwork System—Low Rise

Topic: 
Forced Air
Subtopic: 
System Assessment and Maintenance
Desired Outcome: 
The duct system safely supports peak operation of the equipment
For supporting material, see Referenced Standards and Building America Solution Center.
TitleSpecification(s)Objective(s)
5.3003.36a
Location: indoor (supply ducts) duct section located completely within the thermal boundary Thermal boundary The separation between the interior and exterior environments of a building that slows heat flow of the building

Duct material will be installed with an R-value compliant with code

An appropriate vapor retarder Vapor retarder A material that slows the passage of water vapor and contains a perm rating above 1 will be installed

Prevent condensation on the outside of the ductwork

5.3003.36b
Location: outdoors duct section located outside of the thermal boundary Thermal boundary The separation between the interior and exterior environments of a building that slows heat flow of the building or in quasi-conditioned spaces

Duct material will be selected that meets the following criteria:

  • An insulation level compliant with code
  • Permeability that prevents condensation
  • Permeability that reduces heat loss or gain from the ductwork

Prevent condensation on the outside of the ductwork

Reduce thermal loss or gain from the ductwork

5.3003.36c
Building cavities used as ductwork

When viable building cavities used as ductwork will be replaced with properly sized conventional duct material

When replacement is not an option, building cavities used as ductwork will be sealed when accessible

Safeguard indoor environmental quality

Maximize airflow

Minimize energy use

5.3003.36d
Fire rating

Ducts will be installed in accordance with the fire rating of local codes

Prevent a fire hazard

5.3003.36e
Penetrations

Interior wall penetrations for ductwork will be sealed with a durable sealant (e.g., caulk, silicone, foam)

Penetrations through fire walls and floors will be sealed with a fire-rated material

Prevent a fire hazard

5.3003.36f
Support

Ductwork will be supported in a manner that does not constrict ductwork or duct insulation per SMACNA SMACNA Sheet Metal and Air Conditioning Contractors' National Association, www.smacna.org duct construction standards ( ADC ADC Air Diffusion Council, www.flexibleduct.org for flexible duct or NAIMA NAIMA North American Insulation Manufacturers Association, www.naima.org for fiberglass duct)

Ensure ducts do not sag, bend, trap water, or experience diminished air flow

5.3003.36g
Protection

Ducts will be routed such that service and repair to the building and its systems does not damage the ducts

Protect equipment from damage

Ensure equipment operates as designed

5.3003.36h
Fastening: metal to flexible duct

Flexible duct-to-metal connections will be fastened with tie bands using a tie band Tie band A strap, often made of nylon, that mechanically squeezes a flexible duct to a fitting. Must have a minimum performance temperature rating of 165° (per UL 181A-type test) and a minimum tensile strength rating of 50 pounds tensioning tool

Beaded collars will be installed for all sheet metal to flexible duct connections

Mastic will be applied to interior flex lining to metal connection

Manufacturer specifications will be followed

Ensure duct connections are durable

5.3003.36i
Fastening: metal to metal

Metal-to-metal connections will be fastened with equally spaced mechanical fasteners

Gaps larger than 1/4" will be bridged with sheet metal

Joints will be sealed with mastic

Joints smaller than 1/4" will be sealed with NFPA NFPA National Fire Protection Association, www.nfpa.org 90A and B approved sealant

Ensure duct connections are durable

5.3003.36j
Fastening: duct board to metal

Duct board to metal connections will be fastened with mechanical fasteners

Joints and connections will be sealed with UL UL Underwriters Laboratories 181A listed tapes or mastics

Ensure duct connections are durable

5.3003.36k
Fastening: boot to building connection

Boots will be fastened to the building with mechanical fasteners

Connection will be sealed with mastic, caulk, or gaskets

Ensure duct connections are durable

Properly seal the boots to minimize air leakage

5.3003.36l
Terminations

Terminations capable of delivering air with proper speed and throw of 80-120% of the farthest wall, floor, or ceiling will be selected

Selections will be based on ANSI ANSI American National Standards Institute, www.ansi.org / ACCA ACCA Air Conditioning Contractors of America, www.acca.org Manual T Air Distribution Basics

Deliver and properly mix air in the building

5.3003.36m
Filtration

Filter bypasses will be eliminated

Airtight filter slot covers will be installed to prevent return air leakage in combustion appliance zone

Filters will be changed

Filters with high static pressure drops will be avoided

A visual inspection for excessive dust and debris will be performed, and ducts will be cleaned accordingly

Protect equipment from dirt and debris

Allow for proper airflow

5.3003.36n
External static pressure

Ductwork, filter, and other equipment will be installed so total external static pressure does not exceed manufacturer specifications

Ensure equipment operates as designed

5.3003.36o
Air flow: cooling and heat pump systems

Measured air flow per ton will meet manufacturer specifications

Airflow will be established in accordance with ANSI ANSI American National Standards Institute, www.ansi.org / ACCA ACCA Air Conditioning Contractors of America, www.acca.org 5 QI HVAC HVAC Heating, ventilation, and air conditioning Quality Installation Specification and ASHRAE ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers, www.ashrae.org Standards

Ensure equipment operates as designed

5.3003.36p
Temperature rise: heating-only systems

Temperature rise will be measured, and the result will be in accordance with manufacturer specifications

Ensure equipment operates as designed

5.3003.36q
System protection during construction and renovation

Registers, grilles, and diffusers will be blocked, masked, or otherwise sealed with a durable material

Use of system will not be allowed during renovation or construction

Contractor and occupant will be educated on necessity of protecting the equipment

Protect equipment and occupants from debris in the system

5.3003.36r
Room pressure balancing

An appropriate means of pressure balancing will be installed (e.g., transfer grilles, jumper ducts, individual room returns)

Room-to-room pressure differences shall not exceed +/- 3 pascals with the air handler running

Ensure system has unrestricted airflow between supplies and returns

Minimize infiltration Infiltration The uncontrolled passage of outside air into a building through unintended leaks in the building envelope and exfiltration Exfiltration The uncontrolled passage of inside air out of a building through unintended leaks in the building envelope caused by system

Prevent interference with safe operation of combustion appliances

5.3003.36s
Sealing: new ductwork

Total system leakage (including air handler) will not exceed 20% of designed system airflow (cubic feet per minute) when tested at 25 pascals

For partial duct system replacement or improvement, existing ductwork specification will be applied

Minimize system air leakage

5.3003.36t
Sealing: existing ductwork

Accessible joints, cracks, seams, holes, and penetrations will be sealed

Minimize system air leakage