Hi Tom,

I'm not the pump expert around here, hopefully one of them will be by shortly to answer your post. I will say that my pool is also 18 x 36, and I replaced my motor at 7 years old (my pool is open year round, pump runtime 10-12 hours/day April through October, 3-4 hours/day the rest of the year, overnight during freezing temps, which are rare) with a 1 HP A.O. Smith motor, and it does an excellent job.

Welcome to the forum!!

Janet