The Watts WH-LD restricts the flow to the 3M AP904 Whole House Filter
The 3M AP904 Whole House Filter works as described, but the Watts WH-LD prefilter it says to purchase should be a Culligan WH-HD200-C Whole House Heavy Duty 1" Inlet/Outlet Filtration System. This is what should be used because it has a 1” NPT inlet & outlet which is the same as the 3M AP904 whole House Filter. The Watts WH-LD has a 3/4” NPT inlet & outlet which means if it’s used as a prefilter it would restrict the flow to the AP904. I ended up returning the Watts WH-LD filter for this reason, I didn’t read the specs on the Watts since I figured if they said it was purchased with the 3M AP904 it should be correct.
By Frank Zappettini Jr on June 15, 2018