Hayward H350FDN/P Universal H-Series Vertical Vent Adapter VENT MODEL:UHXNEGVT13508 The EC75A has:

The EC75A has:

Hayward Item Code: SMX306000016

and dual-voltage versions

5" x 2" Check Valve

Hayward Item Code: HLWIRELESS - OmniLogic Waterproof Remote

Hayward H350FDN/P Universal H-Series Vertical Vent Adapter VENT MODEL:UHXNEGVT13508 The EC75A has:Product Description Hayward Universal Forced Draft Negative Vertical Vent Kit Adapter for H350FDN and H350FDP. Hayward Item Code: UHXNEGVT13508 (Adapter Only) This vent kit has been discontinued Features Genuine Hayward Vent Adapter. This vent adapter kit is to be used under negative pressure which is thru roof vertically. Hayward heaters require 1 square inch per 1,000 BTU of fresh air and combustion air supply. Please respect set backs on each side