Furnace Installation and Owners Manual
39
LDJ620_E01_R03_2006.03
Models LDJ620-9 and LDJ620-10
D U C T I N S T A L L A T I O N S T A N D A R D S
The installation guidance presented in this fact sheet should
be followed insofar as it does not conflict with applicable
building codes and the following standards:
Sheet Metal and Air Conditioning Contractors’ National
Association, Inc.
(SMACNA)
Residential Comfort System
Installation Standards Manual (1998, seventh edition) and
Fibrous Glass Duct Construction Standards (1992, sixth
edition). SMACNA’s
HVAC Duct Construction Standards—Metal
and Flexible (1995, second edition), although primarily for
commercial and industrial projects, details good construction
and installation practices that could improve residential
applications.
Air Diffusion Council
(ADC)
Flexible Duct Performance &
Installation Standards (1996, third edition).
North American Insulation Manufacturers Association
(NAIMA)
Residential Fibrous Glass Duct Construction
Standards and A Guide to Insulated Air Duct Systems.
Underwriters Laboratory
(UL) Standard for Factory-Made Air
Ducts and Air Connectors (1996, ninth edition).
G E N E R A L D U C T I N S T A L L A T I O N G U I D E L I N E S
Air distribution ducts are commonly constructed from sheet
metal, rigid fiberglass duct board, or flexible duct. General duct
installation recommendations specific to these different
materials are outlined below. In addition, the air handler,
plenums, and duct boots form parts of the air distribution
system. General installation guidelines for these components
are also provided.
Duct systems should be installed inside the conditioned
(living) and semi-conditioned spaces of the house to the
greatest extent possible (but not in exterior wall cavities). Any
air leakage in ducts located inside the house will not
significantly affect the energy efficiency of the heating and
cooling system because the conditioned air will remain inside
the house. Also, ducts located inside the house need minimal
insulation (in hot and humid climates), if any at all.
Duct systems should be hard-ducted as much as possible.
Duct system installations that use the house structure or
building framing (e.g., building cavities, closets, raised-floor air
handler plenums, platform returns, wall stud spaces, panned
floor joists) as supply or return ducts can be relatively
D U C T I N S T A L L A T I O N P R I N C I P L E S
The objectives of a properly designed and installed duct
system are occupant comfort, proper air distribution,
economical heating and cooling system operation, and
economical duct installation. Such a duct system is one that
•
Provides conditioned air to meet all room heating and cooling
loads.
•
Ensures that the pressure drop across the air handler is within
manufacturer and design specifications.
•
Provides proper air flow.
•
Prevents air from entering the house or duct system from
polluted zones.
•
Maintains a neutral pressure in the house by having balanced
air flows between the supply and return systems.
•
Minimizes duct air temperature gains or losses between the air
handler and supply outlets, and between the return register
and air handler.
During the design of the duct system, the layout and locations
of the ducts are identified, duct materials are chosen, the sizes
of the ducts are calculated, insulation levels are identified, and
registers are selected. Duct installation ensures that the duct
design is achieved in practice by addressing three critical
elements:
•
Mechanical integrity
—the system will remain as built for the
life of the house, without developing leaks, obstructions, or
insulation failure.
•
Freedom from leaks
—all the air moved by the air handler will
be drawn from and delivered to the intended conditioned
spaces.
•
Proper insulation
—conditioned air does not exchange heat
with unconditioned spaces.
