HVAC Equipment and Duct Installation within Conditioned Space
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Summary
Heating, Ventilating and Air Conditioning (HVAC) equipment and, especially, associated ductwork, is often placed in locations such as crawlspaces, attics, and garages. There is an opportunity to have a positive impact on energy efficiency, comfort, and health by instead placing HVAC equipment and ductwork fully inside the insulated and air-sealed shell of the house, known as conditioned space.
Details
While new houses may
have insulation levels of R-15 to R-30 or more, ductwork outside conditioned
space is typically insulated with approximately R-4 to R-6 insulation. Ductwork
and equipment cabinets are also frequently very leaky, drawing in outside air
and/or blowing out air that has been heated or cooled. Research on ductwork
located outside of the conditioned space indicates that between 20 and 35
percent of the energy supplied to them is lost through a combination of air
leakage and conduction. Ductwork and equipment in these areas may also pull in
potentially unhealthy air from crawl spaces and attics. Heated or cooled air
that mixes with outside air due to leaky ductwork is delivered to rooms at
lower or higher temperatures than otherwise, potentially resulting in reduced
comfort.
Installation
Installation of
ductwork may occur in dropped ceilings or interior soffits, within floors
(possibly including insulated slabs), or within attics or crawl spaces that are
designed as conditioned spaces. When this approach is integrated within more
efficient building envelopes, location of outlet registers becomes less
critical, eliminating some of the complexity that may be involved in extending
ductwork to windows and other remote locations.
Caption 1. Proposed dropped Caption 2. Proposed
webbed floor
ceiling or soffit
system for joist
system for two-story houses.
single-story houses.
The figure As in
Figure 1, the sealed combustion
shows a
sealed-combustion in
an inside closet, furnace is located but
furnace located in a closet
indoors supply ducts are
located in the floors. This
and ducts in a dropped ceiling in space
between the space is sealed from
the hallway and
bathroom. The the
wall cavities, to prevent conditioned air
dropped ceiling is
sealed and from
leaking out through the attic.
insulated to prevent
leakage
and heat loss to the
attic.
Benefits/Costs
One benefit of placing
HVAC equipment and ductwork within conditioned space is improved energy
efficiency. Reduced utility costs may be on the order of 20 to 35 percent.
Improved comfort due to higher (or lower) air delivery temperatures, especially
with heat pumps, is likely. Health may be improved as potentially irritating or
harmful items such as dust, pollen, moisture, and radon are not pulled into the
house through leaky ducts, especially those that would have been in
crawlspaces. Lower initial equipment costs may be achieved as required system
heating and/or cooling capacity, and ducts themselves, can be downsized.
Material and installation costs for duct insulation can be avoided. In
some cases, costs for
air sealing ducts can be reduced or avoided when complete duct sealing would
previously have been done. (Note that some, including the EPA, suggest air
sealing ductwork regardless of location to ensure adequate air delivery to
specific rooms, among other reasons).
Limitations
It is possible for
some increase in first-cost due to the need to provide space for HVAC equipment
and ductwork within the house. Design/layout may of the house itself may be
affected, including the need to provide a dedicated utility closet or use
open-web trusses or wooden I-beams in place of solid lumber for floor joists
(open-web trusses and wooden I-joists allow ducts to run easily within floors).
Running ductwork within floors and walls is often more difficult than running
them in generally unconfined spaces like attics and crawlspaces and may also
affect the construction sequence.
Placing combustion
equipment within the house may complicate exhaust duct runs and may pose some increased
risk of exposure to backdrafted combustion products, potentially including
carbon monoxide. Noise from HVAC system fans may be more evident when placed
within the house, although this can potentially be addressed by insulating
around such equipment.
Code/Regulatory
Placing ducts and HVAC
equipment within conditioned space should not require any special code
approval, although certain requirements for supplying combustion air to
furnaces, for example, may apply when these appliances are placed within the
house. In areas where energy codes are in place, this method may allow easier
or alternate methods of compliance. For example, California's Title 24
Efficiency Standards provide an efficiency credit for ducts and HVAC equipment
placed within conditioned space.
Availability
The opportunity to
place HVAC equipment and ductwork within conditioned space is
"available" to any who care to implement it. As full implementation
of this technique is infrequent, it may be difficult to find builders or HVAC contractors
who are experienced with it.
Contact(s)
If you have any
specific questions about this technology and/or its applications please contact
the following resources.
NAHB Research Center
HomeBase Hotline
400 Prince George's
Boulevard
Upper Marlboro, MD
20774
800-898-2842
(Field Guide for
builders on this subject under development)
EPA’s ENERGY STAR
Program
ENERGY STAR Hotline:
888-STAR-YES
ENERGY STAR Homes
Builder Guide
http://www.buildersresourceguide.com/emerging_technologies/hvac_space/hvac_space.html
(2 of 3) [4/12/2001 10:56:06 AM]
http://yosemite.epa.gov/appd/eshomes/eshomes.nsf
Fact Sheet Source
The material provided
in this section is used with permission by the National Association of Home
Builders Research Center and the Partnership for Advancing Technology in
Housing (PATH).
Web sites: