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Education & Training

ACCA: Online Course on Duct Diagnostics & Repair
Air Conditioning Contractors of America online certificate course Duct Diagnostics and Repair is a 3.5 hour online video series that provides guidance that is intended to provide a working knowledge of heating and cooling duct systems, an understanding of the major issues concerning efficiency, comfort, health, safety, and practical tips on diagnostics, installation and repair of duct systems.
Information Sources

Sustainable Building Sourcebook: Ductwork Guidelines
Sustainable Building Sourcebook offers these guidelines for designing and installing good quality ductwork systems. It includes tips for different types of ducting products.
Issues & Performance

Building Science: Air Handler Leakage Testing
Building Science report Air Handler Leakage Testing says the overall duct system tightness is limited by leakage at the air handler. (PDF)

Building Science: Problem With Undercutting Doors For Return Air
Building Science describes problems with undercutting bedroom doors to provide return airflow from bedrooms, along with options for solutions.

CAN/ULC S110-13: Purchasable Standard Methods Of Test For Air Ducts
CAN/ULC S110-13: Standard Methods Of Test For Air Ducts applies to materials for the fabrication of air duct systems for use in accordance with the requirements of the current edition of the National Building Code of Canada. The materials covered by these requirements include preformed lengths of flexible or rigid ducts, materials in the form of boards for field fabrication of lengths of rigid ducts, and preformed flexible connectors. $284 CDN

Energy Vanguard: 4 Ways Bad Duct System Can Lead To Poor Indoor Air Quality
Energy Vanguard describes how a bad duct system can lead to poor indoor air quality.

Energy Vanguard: Sucking & Blowing Lesson In Duct Leakage
Energy Vanguard says whether ducts leak inside or outside the building enclosure is only one leakage location that matters. Your home is also affected by how much leakage occurs on the return side and the supply side of the duct system.

LBL: Duct Leakage Repeatability Testing
Lawrence Berkeley Laboratory report Duct Leakage Repeatability Testing evaluates the repeatability of the three most significant measurement techniques using data from the literature and recently obtained field data. (PDF)

NADCA: ACR Standard For Assessment, Cleaning, Restoration Of HVAC Systems
National Air Duct Cleaners Association developed their ACR Standard For Assessment, Cleaning, and Restoration of HVAC Systems that is an industry standard that establishes criteria for evaluating the cleanliness of HVAC system components, and for cleaning and restoring systems to a specific cleanliness level. Free registration required.

RESNET: 380-2016 Standard For Testing Air Tightness Of Buildings & HVAC Distribution Systems
RESNET and International Code Council have completed their RESNET/ICC 380-2016 Standard for Testing Air Tightness of Building Enclosures, Air Tightness of Heating and Cooling Air Distribution Systems and Air Flow of Mechanical Ventilation Systems. The national US standard provides a uniform methodology for evaluating the airtightness of building envelopes and heating and cooling air ducts and the air flows of mechanical ventilation systems. These test procedures can be used as building diagnostics, in quality assurance and control, for determining compliance with codes and standards and to determine input to energy simulations and ratings. (PDF)

SMACNA: HVAC Air Duct Leakage
SMACNA discusses the history of duct air leak testing and describes proper techniques and practical application when leak testing is performed in accordance with the Sheet Metal and Air Conditioning Contractors’ National Association standards. (PDF)

SMACNA: Residential Comfort System Installation Standards Manual
Sheet Metal and Air Conditioning Contractors' National Association sells the Residential Comfort System Installation Standards Manual. It covers installation standards for residential heating and cooling systems including load calculations, duct design, duct construction, insulation, vents, air terminals, control applications, system specifications and industry equipment and methods for residential systems. Also covered are forced air heating, heat pumps, automatic control thermostats, flues and sound and vibration. Includes soft metrics. $108 USD

SMACNA: Standards For Duct Air Leakage Testing
SMACNA lists industry standards and codes that follow the SMACNA method of duct air leakage testing. (PDF)

ACCA Now: How To Diagnose & Repair Duct Leakage
ACCA Now says there are obvious areas, but in no way are these the only areas that require sealing in order to have an efficient duct system.

ACCA Now: Properly Sizing Return Duct Systems
ACCA Now describes how an undersized return duct system reduces the amount of air flow through the system and may cause reduced comfort and efficiency as well as poor supply airflow, duct sweating, improper refrigerant charge, and excessive air noise.

ACCA Now: Use Static Pressure Measurement to Pinpoint Duct Deficiencies
ACCA Now looks at how static pressure measurements quickly verify duct systems health via installed performance.

ACCA: DuctWheel For Duct Sizing Now Available As iPad App
Air Conditioning Contractors of America now offers their DuctWheel duct sizing as a software application for the iPad. It is available for purchase in Apple's iTunes store.

ACHR News: Residential Air Flow Balancing & Home Comfort
ACHR News says this home is an ideal example to demonstrate how residential air flow balancing works, how to overcome challenges and how this practice can benefit your business and customers.

ASHRAE: Duct Sizing Calculator Available
A new duct sizing calculator from ASHRAE and the Air Distribution Institute allows HVAC air distribution system designers to more accurately size ducts, especially flex ducts under varying amounts of compression,

BC Housing: Avoiding Exhaust Duct Problems
BC Housing bulletin Avoiding Exhaust Duct Problems explains the importance of a well-maintained system and helps homeowners identify and solve common issues with ducting around the home. (PDF)

Building America: Ducts In Dropped Ceilings
Building America Solution Center online guide describes the method for installing ducts in a duct chase above a dropped ceiling.

Building Performance Community: Online Video On Duct Sealing
Building Performance Community online video Duct Sealing for Comfort, Energy and Indoor Air Quality shows how ducts move air, where common leaks are, and how to fix them.

Building Science: Duct Dynasty & Ducts In Attic
Building Science describes issues and considerations for putting ductwork in an attic.

Building Science: No Sweat Ductwork In Attics
Building Science describes options, issues and considerations for placement of ductwork so as to prevent sweating on ducts.

Building Science: Sizing HVAC Ducts, Trunks, & Runouts
Building Science provides a design process for sizing cooling and heating system capacity for energy efficient housing; for specifying the airflow and duct sizes to each conditioned space; and for specifying the free area needed to transfer air supplied to closed rooms back to the central return.

Building Science: Transfer Grilles Facilitate Return Air Flow
Building Science paper says transfer grilles represent a cost-effective alternative to individual return ducts if they are properly configured for air flow, privacy, and aesthetics. (PDF)

CMHC: Garbage Bag Airflow Test For Duct Airflow
CMHC fact sheet explains how to make and use a simple garbage bag device to measure airflow coming out of supply air diffusers and flowing into return air grilles. (PDF)

EAI: Building With Ducts In Conditioned Spaces
Earth Advantage Institute online guide Building with Ducts in Conditioned Spaces will help designers, architects, general contractors and sub-contractors work together to install ducts inside the thermal boundary to reduce heating and cooling costs, increase energy efficiency, improve occupant comfort, and if skillfully done to also reduce construction cost. (PDF)

Energy Conservatory: Using Duct Blaster To Test Duct Tightness
Energy Conservatory online four-part video series describes how to test duct tightness using the Duct Blaster.

Energy Conservatory: Using Minneapolis Duct Blaster To Test Leaky Ducts
Energy Conservatory online slide show describes how to use the Minneapolis Duct Blaster to perform duct leakage tests. (PDF)

Energy Vanguard: 17 Steps to Better Duct Systems
Energy Vanguard offers a compendium of tips for duct design and installation.

Energy Vanguard: Determining the Zones in Duct Design
Energy Vanguard describes issues and considerations for determining duct zoning.

Energy Vanguard: Duct Design, Available Static Pressure
Energy Vanguard describes how to choose a blower that will give the total air flow needed, and how to design a duct system that will deliver the proper amount of air to each room. To do that, you need to take the concept of pressure drops and apply it to blowers and ducts.

Energy Vanguard: Duct Design, Basic Principles
Energy Vanguard describes what you do in the HVAC design process before you get to the duct design phase as well as the physics of air flow when it's constrained by ducts.

Energy Vanguard: Friction Rate Is the Wrong Name
Energy Vanguard says friction rate confuses a lot of people because it's the wrong name. First they tell you why and then what they think we should be calling it.

Energy Vanguard: Invisible Problem With Duct Insulation
Energy Vanguard discusses a problem that seems to be invisible: the inadequacy of duct insulation even when the design and installation are perfect.

Energy Vanguard: MAD AIR, Duct Systems, Infiltration, & Their Interactions
Energy Vanguard says a paper, MAD AIR: Mechanical Air Distribution And Interacting Relationships showed that duct leakage can have a big effect on the pressure in a home, and so can closing bedroom doors and airtightness of the homes.

Energy Vanguard: Moving Air Efficiently Through Your Duct System
Energy Vanguard describes secrets to moving air efficiently through your duct system.

Energy Vanguard: Sizing Ducts
Energy Vanguard describes how to decide how big ducts need to be, following the Manual D protocol for duct design, a standard developed by the Air Conditioning Contractors of America.

Energy Vanguard: Third Worst Place to Put a Duct
Energy Vanguard says putting supply vents in exterior walls is bad for several reasons.

Energy Vanguard: Two Primary Causes Of Reduced Air Flow In Ducts
Energy Vanguard describe how friction and turbulence play a big role in whether a duct system does what it's supposed to or not.

Energy Vanguard: What Happens to Air Flow in Ducts When Size Changes?
Energy Vanguard discusses what happens to air flow in ducts when the size changes.

Fine Homebuilding: Hiding Ducts In Conditioned Space
Fine Homebuilding describes how to install and hide ducts in conditioned space.

Fine Homebuilding: HVAC Duct Sealing & Leak Testing
Fine Homebuilding online video features duct sealing experts explaining how to seal leaks in duct seams and how to conduct a duct leakage test.

GBA: Duct Leakage Testing
Green Building Advisor describes how to seal heating duct seams with mastic and test them with a Duct Blaster for an energy-efficient forced-air system.

GBA: Ductwork for ERVs, Dehumidifiers, Forced-Air Systems
Green Building Advisor discusses whether it is possible for an ERV, a whole-house dehumidifier, and a forced-air heating and cooling system to share ductwork.

GBA: How To Track Down Leaks In Forced Air Ductwork
Green Building Advisor says leaky ducts in a forced-air heating and cooling system are an all-too-common problem, and discusses whether or not ducts can be effectively sealed from the inside.

GBA: HVAC Duct Design Issues & Ideas
Green Building Advisor describes how a presentation by David Hill suggested good duct design includes examining the way we do duct take-offs and fittings, placing an evase between the fan outlet and the trunk, looking very carefully at filter placement and the taughtness of flex duct, and start doing all this in the design phase.

GBA: Is Bubble Wrap Duct Insulation A Good Idea?
Green Building Advisor says although reflective layers can be effective when installed correctly, they aren't the best way to insulate ducts.

GBA: Issues With Foil Bubble Wrap Duct Insulation
Green Building Advisor forum discusses considerations and issues with using foil bubble wrap to insulate HVAC ducts.

GBA: Keeping Ducts Indoors
Green Building Advisor says you should keep ducts indoors, and describes five ways to bring ducts inside a home’s conditioned space.

GBA: Raining, Dripping, Crying Duct Boots
Green Building Advisor describes why to insulate and seal the duct system. Not doing so can cause the central air conditioner's ceiling registers to drip onto the floor, the insulation liner on the duct in the crawlspace to hold a gallon or two of water, or the office that has spots appearing on the ceiling.

GBA: Return-Air Problems
Green Building Advisor says in homes with a single central return-air grille, return air often struggles to find its way back to the furnace.

GBA: Simple Methods For Measuring Air Flow
Green Building Advisor describes simple methods for measuring air flow including homemade flow hoods, the credit card test, the garbage bag test, and calibrated laundry baskets.

GBA: Thou Shalt Commission Thy Ducts
Green Building Advisor says if you don't commission new HVAC systems in high-performance homes, you're gambling with callbacks.

GBA: Using Tape Or Mastic For Sealing Ducts
Green Building Advisor describes how to choose tape or mastic products that provide durable sealing for ducts.

Healthy Indoors: An Air Duct Cleaning & HVAC Hygiene Primer
Healthy Indoors says duct cleaning refers to the cleaning of heating, ventilation and cooling systems, including their associated air ducts and components.

HPAC Magazine: End is Near for Whole House Ducted HVAC
HPAC Magazine says a house purchased in 1975 may well be on its second or third HVAC system, and it may have new windows and better insulation; however, the original duct system, designed for a furnace long since recycled into beverage cans, likely requires considerable renovation expense to suit today’s blowhard gas furnaces.

HVAC School: Cutting & Installing a Rectangle Duct Connection
HVAC School online video shows how to cut and install a rectangle duct connection.

HVAC School: Friction Rate Chart & What it Means
HVAC School says a lot of proper duct design comes down to a understanding of available static pressure and friction rate. Here they focus on this ACCA chart specifically.

HVAC School: How to Determine Friction Rate for Residential Duct Design
HVAC School says there is some confusion on what friction rate is and what friction rate to use with a duct calculator. Hopefully, after reading this tech tip you will have a better understanding.

HVAC School: How to Make a Metal Duct Transition in the Field
HVAC School online video provides a detailed demonstration of how to make a metal duct transition in the field.

HVAC School: Sealing Duct Boxes, Boots, Cans
HVAC School says whenever you are installing duct boxes (also called boots or cans) in an aftermarket application, make sure to place a bead of sealant like mastic or silicone on the flange so that as it presses against the substrate it will seal against leaks to and from the unconditioned space.

HVAC School: Size & Orientation of Return Grilles & Supply Registers
HVAC School says proper sizing and orientation of grilles, registers, and diffusers may seem like such a simple thing, but it's an area where confusion and mistakes are commonly made.

HVAC School: The Ten Duct Commandments, Plus a Few More
HVAC School describes some fundamentals for designing and installing duct systems, and also includes links to some great resources.

JLC: Testing Home Ductwork For Leaks
Journal of Light Construction online video provides an introduction to performing tests for air-tightness of heating and cooling ducts.

Mechanical Business: Rethinking Duct Design Practices
Mechanical Business says with recent changes to the CSA F280 Standard, Determining the Required Capacity of Residential Space Heating and Cooling Appliances, we are going to see the use of smaller furnaces and air conditioners in homes, and the rethinking of appliance sizing should also lead to a rethink of duct sizing as well.

NADCA: FAQ's On Residential Duct Cleaning
National Air Duct Cleaners Association represents this relatively new industry and has some good consumer info that cautions against being oversold on duct cleaning.

NRC: Evaluating Duct Cleaning In Commercial Office Buildings
National Research Council Canada report Testing Effectiveness of Duct Cleaning and Its Impact on Airborne Particles, Mold and Biocide Levels in Commercial Office Buildings is a guide which will allow building operators or facility managers to assess whether duct cleaning work was successfully and appropriately performed in terms of cleanliness of the air ducts as well as meeting expectations concerning the quality of the resulting supply air. (PDF)

NREL: Air Distribution Basics & Duct Design
US National Renewable Energy Laboratory guideline Air Distribution Basics and Duct Design describes how the energy efficient house design process offers opportunities to integrate the HVAC system into the design earlier in the process and to utilize a strategy of shorter duct runs with smaller cross-sectional areas that can reduce system costs and that can be installed completely within the conditioned space. (PDF)

NREL: Air Mixing & Thermal Comfort From High Sidewall Supply Air Jets
National Renewable Energy Laboratory provides information to guide the selection of high sidewall air supply inlets to maintain proper room mixing for heating and cooling of high performance homes. (PDF)

NREL: Designing Interior Ducts In New Construction
US National Renewable Energy Laboratory report Measure Guideline: Summary of Interior Ducts in New Construction, Including an Efficient, Affordable Method to Install Fur-Down Interior Ducts, describes a variety of methods to create interior ducts including the fur-up chase method, the fur-down chase method, and interior ducts positioned in sealed attics or sealed crawl spaces. (PDF)

NREL: Sealing & Insulating Ducts In Existing Homes
US National Renewable Energy Laboratory guide Insulating Ducts in Existing Homes discusses potential cost and performance benefits of duct sealing and insulating, reviews of typical duct materials and components, and describes overall procedures for assessing and improving the duct systems. (PDF)

ORNL: Case Studies Of Duct Retrofits & Guidelines For Attic & Crawl Space Duct Sealing
Oak Ridge National Laboratory report Case Studies of Duct Retrofits and Guidelines for Attic and Crawl Space Duct Sealing focuses on sealing and insulating ducts in unconditioned spaces, with best practices geared toward the mixed-humid climate. (PDF)

RCD: Duct Sealing Tips
RCD describes how to seal air ducts of heating systems.

Today's Homeowner: How to Insulate HVAC Heating and Cooling Ductwork
Today's Homeowner offers how-to steps for insulating all HVAC heating and cooling ductwork.

US DOE: Better Duct Systems for Home Heating & Cooling
US Department of Energy bulletin Better Duct Systems for Home Heating & Cooling provides a working knowledge of residential heating and cooling duct systems. It includes an understanding of the major issues concerning efficiency, comfort, health and safety, as well as practical tips on installation and repair of duct systems. (PDF)

US DOE: Buried & Encapsulated Ducts
US Department of Energy report Buried and Encapsulated Ducts evaluates insulating ducts in unconditioned space in three homes in Florida. This technique can reduce duct thermal losses, which can range from 10%-45% in single-family homes. (PDF)

US DOE: Compact Air Distribution System
Building America Solution Center describes features, benefits, issues and considerations for design and installation of compact duct systems.

US DOE: Encapsulated Ducts With Spray Foam
Building America online Solution Center Guide illustrates how and when to encapsulate ductwork in unconditioned attics to increase R-value, mitigate condensation issues and reduce air leakage.

US DOE: Injected Spray Sealant For Existing HVAC Ducts
Building America Solution Center describes features, benefits and considerations for installing injected spray sealant for existing HVAC ducts.

US DOE: Jump Ducts
US Department of Energy describes features, issues and considerations for installing jump ducts that provide for pressure balancing between rooms of a house.

US DOE: Residential Duct Systems for New & Retrofit Homes
US Department of Energy online slide show presentation describes features, issues and considerations for residential duct systems for new and retrofit homes. (PF)

US DOE: Sealed & Insulated Metal Ducts
US Department of Energy describes issues and considerations for installing sealed and insulated metal ducts.

US DOE: Sealing & Insulating Ducts In Existing Homes
US Department of Energy online Measure Guideline: Sealing and Insulating Ducts in Existing Homes covers potential cost and performance benefits of duct sealing and insulating, typical duct materials and components, and overall procedures for assessing and improving the duct system. (PDF)

US DOE: Sealing Duct Boots to Floor or Drywall
US Department of Energy describes issues and considerations for sealing connections between grilles, registers and ducts at ceilings, floors or knee walls that typically leak where the boot does not seal tightly to the grille or gypsum board.

US DOE: Strategies For Existing Ducts When HVAC Downsized
US Department of Energy report Overcoming Comfort Issues Due to Reduced Flow Room Air Mixing discusses feasibility of modifying the duct systems using minimally invasive strategies to improve air distribution when HVAC equipment is downsized and ducts are unaltered. (PDF)

US DOE: Transfer Grilles
US Department of Energy describes features, issues and considerations for transfer grilles that provide for pressure balancing between rooms of a house.

US EPA: Should You Have The Air Ducts In Your Home Cleaned
US Environmental Protection Agency site covers all information required to know about when and how they should be cleaned.
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