My feedback on main drains in an above ground pool...

[mas985]

Not at all... It is a very simple principle that you have been arguing against aimlessly for this entire thread. Simple, cool water sits at the bottom. Warm water at top. Cool water gets sucked in, warm water gets injected. Complete turnover with the shortest amount of time. You will NOT have that without pulling water from the furthest, lowest point of the pool while returning water at a higher further point away. C'mon, how hard is that to understand??!?!?!?

I understand that very well and was not arguing that point at all. But the effect only occurs as long as there is a temperature difference between the surface and the bottom. My main point is that after the pump turns on, any temperature difference disappears very quickly (< 30 min) because the returns mix the water pretty effectively. So I fail to see how the heating efficiency is going to be affected that much by a main drain especially when the pool is only 4' deep. I maintain that it will still take about the same amount of time to heat a pool 1 degree with or without a main drain (~40 min) and if you measure the temperature difference of the top vs bottom of the pool, it will be about the same after about 30 min.

Remember too that this site and other pool sites recommend a 30 min run time to fully mix added chemicals throughout the pool so there is precedence to the fact that mixture of chemicals, and by proxy heat, throughout the water usually occurs within about 30 min.