How much heater?

[threedog]

I need to replace the pool heater, I have an in ground 40,000 gallon pool with a 400 gallon hot tub. My heater was for the pool and hot tub, now I just want to heat the hot tub. Never did heat the pool, but enjoy the hot tub all year.

So, How much heater (gas) do I need for the hot tub. I'm in South Carolina.

Thanks,

Threedog

[muss08]

What is your average ambient air temp and how hot do you want to heat the spa?