With George Watts and skipper Danny Cox scoring 30 not out and 24 respectively, Ventnor reached 134-4 before skittling Northwood for a paltry 38, Charlie Calloway and Watts taking two wickets each.
Off-spinner Cox (2-16) and Will Mew (2-17) did the damage as St Helen's (who beat Porchfield in their semi-final) were dismissed for 76 in the final, Ventnor, 52-3 at one stage, winning by three wickets through an unbeaten 26 by Toby Noyes.
Ventnor will represent the IWCB in 2025 ECB indoor championships.