Efficiency Values for Dryer Exhaust Terminations and Fittings

Dryer vent hoods come in a multitude of styles and end up in one of three locations on your home: the roof, the soffit or the wall. The objective of a vent hood for the dryer is basically two fold; prevent back drafts and prevent bird or rodent entry as well as nest building. In facilitating these capabilities a prevalent result is a vent hood that promotes lint build-up and creates excessive back pressure.

Magnehelic Gauge A vent hood or fitting that creates excessive back pressure not only lengthens the drying cycle but accelerates dangerous lint build-up. Higher energy bills and increased risk of fire become the obvious outcome. Until now, there was no assessment of the back pressure that these popular vent hood designs and fittings provide. The below chart provides the actual difference or delta (∆) of air pressure measured with a Magnehelic Gauge* before and after the fitting was attached (Differential Pressure). The higher the value, the less efficient the fitting is. These days, being energy efficient is important step in the direction of drying smart. Consider these values when shopping for a dryer vent fitting or hood.

Legend .05 - .10 — Efficient .11 - .21 — Sufficient .21 - .29 — Restrictive

Airflow Efficient Ratings Matrix by Product

Fitting Type Description Model ID Thumbnail Buy Airflow Reduction (wci)*
Roof DryerJack 466 DJK466 N/A .00
  DryerJack 486 DJK486 .02
  Roof Jack Plastic Not Carried N/A .35
  Popular Broan Style Not Carried N/A .30
  Typical 4" Wide Goose-neck Not Carried N/A .45
  New Mushroom Style Not Carried N/A .25
Wall Dryer Wall Vent DWV4 .00
  4" Louvered Vent GH4W .08
  No Nest Vent NO NEST N/A .01
  3 Louver Opening Vent HS4W .03
  Dryer Vent Closure Not Carried N/A .60
  Standard 30° Wall Flapper Not Carried N/A .20
Eave Under Eave Vent EVEVENT .10
Fittings Sectioned 90 Degree Elbow ELL-4 N/A .15
  Dryer-Ell 10 Inch Radius 90° Elbow LT90 .05
  Dryer-Ell 10 Inch Radius 45° Elbow LT45 .05
  Close Ell CLOSE-ELL .25
  Lint Trap ECCO Lint Trap N/A .15
  Periscope Style Connector Not Carried N/A .50
Flex Foil Wire Bound Not Carried N/A .35
  Semi Rigid Alum Flex ALUM-439 N/A .10
  Semi Rigid Alum Flex ALUM-448 N/A .10
*Difference with and without fitting, measured with a magnehelic gauge.

*Magnehelic Gauge: A sensitive differential pressure or vacuum gauge manufactured by Dwyer Instrument Co. that uses a precision diaphragm to measure pressure differences. This gauge is manufactured in specific pressure or vacuum ranges such as 0 to 2 inches of water column. Airflow was provided by a typical residential clothes dryer.