The questions is in regards to the LEED Reference guide for green building design and construction, 2009 Edition, IEQ Prerequisite 1 - Minimum indoor air quality performance (pg 407), Case 1 - Mechanically Ventilated Spaces states "Meet the minimum requirements of sections 4 through 7 of ASHRAE 62.1, 2007 Ventilation for acceptable indoor air quality". In ASHRAE 62.1 section 5.9, Particulate Matter Removal, it states "Particulate matter filters or air cleaners having a minimum efficiency reporting value (MERV) of not less than 6 when rated in accordance with ANSI/ASHRAE Standard 52.215 shall be provided upstream of all cooling coils or other devices with wetted surfaces through which air is supplied to an occupiable space. The question is on Mini Split units (Wall mounted recirculating type with no outside air and Ceiling Cassette type with pre treated outside air) are these units required to have a minimum of a MERV 6 filter. My interpretation is that ASHRAE 62.1 is meant to provide a standard for filtering the outside air being brought into the building for ventilation. Therefore, if the dedicated outside air unit is filtered per ASHRAE, does the minimum MERV 6 filter rating apply to mini split systems which are really recirculating air and supplying pretreated/prefiltered outside air if any? Residentially Per ASHRAE 62.2-2010, ducted mechanical systems are those that supply air to a space that can be occupied through ductwork exceeding 10 feet in length and through a thermal conditioning component, except for evaporative coolers. Systems that do not meet this definition are exempt from this requirement. Also, mini-split systems typically do not have MERV-rated filters available for use and are, therefore, also exempted under this version of the guidelines. Commercially I could not find anything in which spells out the above for residential applications. Thank you for your time