Distribution and Room Air Mixing Risks to Retrofitted Homes

Stacey Rothgeb, A. Burdick, Stacey Rothgeb (NREL Technical Monitor)

Research output: NRELSubcontract Report


Energy efficiency upgrades reduce heating and cooling loads on a house. With enough load reduction and if the HVAC system warrants replacement, the HVAC system is often upgraded with a more efficient, lower capacity system that meets the loads of the upgraded house. For a single-story house with ceiling supply air diffusers, ducts are often removed and upgraded. For houses with ducts that areembedded in walls, the cost of demolition precludes the replacement of ducts. The challenge with the use of existing ducts is that the reduced airflow creates a decreased throw at the supply registers, and the supply air and room air do not mix well, leading to potential thermal comfort complaints. This project investigates this retrofit scenario. The issues and solutions discussed here arerelevant to all climate zones, with emphasis on climates that require cooling.
Original languageAmerican English
Number of pages28
StatePublished - 2014

Bibliographical note

Work performed by IBACOS, Inc., Pittsburgh, Pennsylvania

NREL Publication Number

  • NREL/SR-5500-63155

Other Report Number

  • DOE/GO-102014-4544


  • air distribution
  • Building America
  • cooling
  • HVAC
  • leakage
  • pressure
  • register sizing
  • residential
  • residential buildings
  • spread
  • stratification
  • throw


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