NLA - Hayward UHXNEGVT11501 H150FD Indoor Vertical Vent Adapter Kit - Neg Pressure

Negative-Pressure Ventilation is for a vertical or straight up or almost straight up vent pipe where the heat rise creates lift and minimal condensation will form in the pipe. Positive-Pressure Ventilation is for a more horizontal application venting application where the heat rise is less and there is a chance of more condensation in the pipe that will cause rusting and damage.