HVAC Equipment and Duct Installation within Conditioned Space Installing HVAC within conditioned space improves energy efficiency, comfort, and health  Heating, Ventilating and Air Conditioning (HVAC) equipment and associated ductwork, are often placed in crawlspaces, attics, and garages. However, there is an opportunity to improve energy efficiency, comfort, and health by instead placing HVAC equipment and ductwork inside the insulated, air-sealed shell of the house, known as conditioned space.
While new houses may have wall and ceiling insulation levels of R-15 to R-30 or more, ductwork outside conditioned space is typically insulated with 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 conditioned space indicates that between 20 and 35 percent of the energy supplied 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. 
 | By reducing losses of conditioned air to unconditioned space and infiltration of unconditioned air to the ducts, less energy is spent to condition the house to its desired temperature. |  | By keeping leaked, conditioned air in conditioned space, temperatures stay relatively stabel and air quality is not as susceptible to any outside pollutants. This allows for a healthier home environment. |
The opportunity to place HVAC equipment and ductwork within conditioned space is "available" to any who care to implement it. However, in some regions it may be difficult to find builders or HVAC contractors who are experienced with it. There may be an increase in first-cost due to the need to provide space for HVAC equipment and ductwork within conditioned space. Design and layout of the house may also be affected, in order to provide a dedicated utility closet, or to use open-web trusses or wooden I-beams in place of solid lumber for floor joists to allow ducts to run easily within floors. Running ductwork within floors and walls may be more difficult than running them attics and crawlspaces. Placing combustion equipment within the house may complicate exhaust duct runs and may pose an increased risk of exposure to backdrafted combustion products, including carbon monoxide. Noise from HVAC system fans may be more evident when placed within the house, although equipment can be insulated.
Initial costs will likely be higher because of the possibility of installing drop ceilings, a system closet, and possible roof deck insulation.
This system setup will likely reduce energy losses because all leakage is occuring in conditioned space. In this sense, energy bills will be reduced.
Placing ducts and HVAC equipment within conditioned space does not require special code approval, although supplying combustion air to furnaces may be required when these appliances are placed within the house. In areas where energy codes are in place, there may be efficiency credit for ducts and HVAC equipment placed within conditioned space.
Carl Franklin Homes: The Vista at Kensington Park, Dallas, Texas Hughes Construction: Lexington, North Carolina K. Hovnanian Inc: College Park Estates. Freehold Township, New Jersey MADE Project: Bowie, Maryland Warren Builders: Site 1. Albertville, Alabama
Ductwork can be installed 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 HVAC equipment and ductwork are placed within an insulated building envelope, 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.
Not Applicable
A benefit of placing HVAC equipment and ductwork within conditioned space is improved energy efficiency. Reduced heating and cooling costs may be on the order of 20 to 35 percent, or up to $200 per year for the average home. Improved comfort is also likely. Health may be improved, as potentially irritating or harmful dust, pollen, moisture, and radon are not pulled into the house through leaky ducts, especially those in crawlspaces. Initial equipment costs may be reduced because 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. | 
