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Basic Residential
Ductwork Design |
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Understanding Basics
of Residential Ductwork Design is the key to ensuring your entire heating and
cooling system is
adequate and efficient.
This page and all of its content is intended as a guideline from which to understand the basic principles of
Residential Ductwork
Systems and their design. Hamilton Home Products, Inc. recommends that all
Residential Ductwork Systems be designed and installed by a qualified
technician. |
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Understanding Basic Residential
Ductwork Design
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Please Note: All
information provided in this document is to be used as a guideline only.
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The purpose of Residential Ductwork Design is to properly distribute
the airflow,
produced by your heating/cooling system, to your house. This involves Return Air (unconditioned)
coming into the heating/cooling system. Then, by
heating/cooling that air,
delivering the newly conditioned air to your home. An improperly designed
ductwork systems can cost money through inefficiencies, and in some cases, cause
premature failure of heating and cooling equipment. This means that your
home's ductwork system is just as important as the equipment used to heat and
cool your home.
The 3
Most Important Things to Understand About Residential Ductwork Designs are:
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Furnaces and air conditioners require a certain
amount of airflow, measured in CFM
(Cubic Feet Per Minute), to be passed through the equipment (supply and return
ducts) in order for the equipment to function properly and efficiently.
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All homes have unique requirements and construction
that pose obstacles when designing the ductwork system to accommodate each
room with proper airflow. (This is especially true with
older homes.)
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The Ideal Ductwork System achieves both goals
by providing enough
airflow to and from the heating/cooling equipment as well as the home. For
maximum efficiency, this
"ideal" system should also be sealed at all seams with aluminum tape,
and should be properly insulated when exposed to unconditioned environments
(i.e. crawl spaces and attics).
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A Common
Ductwork Design
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Please Note: All
information provided in this document is to be used as a guideline only.
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CLICK TO ENLARGE |
This type of system incorporates the use of a "Trunk Line" or series of
Rectangular Ducts that act as a main supply channel throughout the house.
From these "Trunk Lines" come branch ducts (usually round) that extend, in
various ways, to the registers which are strategically placed throughout the
home.
The size of each
component is determined by the airflow that needs to pass through it.
The overall sizing of the "Trunk Line" is designed to evenly distribute
the appropriate amounts of air to every register.
Caution must always be used when sizing
individual components to insure that the heating/cooling equipment has
adequate airflow for optimum performance. |
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Rectangular Duct and
Round Duct
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Please Note: All
information provided in this document is to be used as a guideline only.
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CLICK TO ENLARGE |
Please Note: All
information provided in this document is to be used as a guideline only.
The duct
sizes listed in the chart provided are based on a fraction drop of .10
inches per 100 feet of lineal duct. This "Equal-Friction" method of duct
sizing should be adequate for normal residential furnace heating and air
conditioning applications. Larger volumes or higher static pressures should
be dealt with on an individual job basis. |
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CLICK TO ENLARGE |
Example: Ductwork Design
Layout (With CFM Ratings)
This system is designed to
move 3 Tons of Air Conditioning or 1200 CFM. |
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Basic Guidelines for Ductwork
Fittings and Placement
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Please Note: All
information provided in this document is to be used as a guideline only.
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Supplies
are located on outside walls.
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Returns
are located on inside walls. They should not be located in the same area as
the furnace, nor should they be located by moisture sources such as kitchens
or bathrooms.
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Return
Air CFM must be equal or greater than Supply Air CFM.
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Wyes
commonly reduce.
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Tees
split, but do not reduce, and an appropriate reducer must be added.
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Dampers
on take-off duct runs allow for adjustments of air distribution.
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In order
to maintain velocity, reduce duct size.
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Never
locate ducts at the end of the trunk line run. Last take-off run to be
located 12" - 18" from end.
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Always
stagger take-off ducts by 12" to maintain pressure.
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Use
insulated duct or duct board in unheated spaces.
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Flexible
duct work must be stretched tightly for maximum air flow.
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Ductwork
FAQ's and Government Publications
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Please Note: All
information provided in this document is to be used as a guideline only.
Hamilton does not
necessarily endorse or agree any information provided on these sites.
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Air
Distribution System Installation (Adobe® PDF)
US Department of
Energy
This
Technology Fact Sheet explains the need for efficient duct systems, how
inefficient systems can cost you money and how they can cause health problems.
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Ductwork
Install Guide (Adobe® PDF)
Air Diffusion
Council
Various
guidelines (with reference to various codes) for basic flexible ductwork
installation, including illustrated examples for connecting, joining, and
splicing flexible ducts.
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Energy
Efficiency in Remodeling: Ducts
(Adobe®
PDF)
This fact sheet was prepared
by NAHB Research Center, 400 Prince George's Boulevard, Upper Marlboro, MD
20774, (800) 638-8556, with support from the
US Department of
Energy and the
National Renewable Energy Laboratory.
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Should You Have the Air
Ducts In Your Home Cleaned? (Adobe® PDF)
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(EPA)
Environmental Protection Agency
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This fact
sheet helps to explain the facts and fiction about air duct cleaning. There are
also tips for what to look for when having your system inspected, and when to
have your air ducts cleaned.
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