mas985 wrote:It depends on the size of your pool but a 116 BTU heater will raise 10000 gallons of water about 1.4 degrees per hour. 20000 gallons 0.7 degree per hour.
This may be true in a perfectly controled enviroment as of an indor pool.
There can hardly be calculated input of the outdor element involved, such as current outside temperature, wind direction, etc.
Thing to remember is that your water will not warm up much until it warms up the surrounding gunite.
Simmilar to warm up of soup, that was kept in the fridge in a Corningware pot.
Vinyl in the sand may have different rate of a warm-up.
While you injecticting warmer water into the pool, gunite is absorbing the heat and cold wind is stripping it, as you constantly exposing just warmed up water to the surface.
The tables may give you a general idea of rate of the warm up, but only experience of a particular location combined with the current outside element will tell you, if the picked weekend will be economical to fire up your heater.