MERV 13 filters

There is new legislation on the subject. Here is a link to the "LEED Addenda" website. http://www.usgbc.org/DisplayPage.aspx?CMSPageID=2200#BD+C Because this is new legislation I can only give you my interpretation: The intention of the correction is to clarify where the MERV 13 filters should be located inside an AHU that supplies OSA and recirculate air. The filter should not be at the OSA damper, but instead downstream of the mixing of the return air and the OSA to filter both the OSA and recirculated air. However, an indoor fan coiling unit or heat pump that is recirculating air to condition a space would not require MERV 13 if it is not pulling air directly from outside. Even if there is a DOAS providing OSA air into a mixing boxing in the back of the FCU/heat pump, it should still not require a MERV 13 filter (only MERV 8 for ASHRAE). The MERV 13 filter would be in the DOAS. The legislation was changed in the first place because FCU's can't handle the pressure drop from a MERV 13 filter - I don't believe this legislation was intended to put that requirement back.