Pool heaters

[ian121]

hi i have an above ground 21foot by 12foot pool im going to buy a 5kw electric heater for it but i have a quick query i live in the uk and dont have the room for extra pipes for solar heating, i have a 3kw heater which aint powerful enough to heat the pool fully so if i buy a 5kw can i put them both inline? in other words have the water running through the 3kw heater set to say 15 degrees c then about another foot further on have the 5kw set to say 25 degrees c so the water going into it is already on its way to 15 c the cost of electric to run the heaters doesnt matter cos i can run them both for free but will it make a difference having two or will there be no benefit?