Why not go with a heatpump instead? A heatpump generally has the lowest operating costs after solar. As for 100,000BTU/Hr I would think that enough if you use the solar cover. I have an 85,000 BTU/HR heatpump on my 20 x 40inground pool and that is more than enough to get the pool as hot as I want. Well I have never gone over 88 degrees, but I am sure it would go higher if I wanted

An above ground pool should require LESS heat input as the walls are in contact with summer air as opposed to an inground that is in contact with the cool ground.