Expect, with a 400K heater, about $12/hour, roughly and just under a 1 degree/hour rise.

Scott

Thanks. Are you referring to using a heater for the pool? Or using the spillover from the hot tub to heat the pool?

The spa and the pool should both be getting water at the same time so they both will get warmed by the heater at the same time.

During a normal filter mode, the valve that sends water to the pool or spa should be cracked so freshly filtered and chlorinated water does to both. This will also skim the spa since it doesn't have a skimmer. Since the heater is connected to the filter before that valve, the heater can heat both. When in SPA mode, the valve sending water to the pool and spa closes off the pool and the suction valve shut off the pool suction. This makes a very small body of water for the heater to heat to your liking, say 100 from 85 in about 10 to 15 minutes.

Scott

It takes 8.34 BTU's to heat 1 gallon of water 1 degree F. so 48,000 gal * 8.34 BTU/gal = 400,320 BTU per degree of water temperature rise (Assuming you lost no heat from evaporation, which obviously you will).

1 CCF of natural gas has 101,500 BTU. So it basically takes 4 CCF's of natural gas to heat your water 1 degree F. Here in Houston for example, a CCF of natural gas currently goes for $0.76, so with a 400K BTU heater, it would cost $3.04/hour to run. Roughly $3 per degree of temperature rise - (probably under-estimated as you will be loosing heat off the surface of the pool while heating it up. Solar or thermal blankets across the top of the pool would help.

Using Propane, you get 91,700 BTU per gallon, so 400,320/91,700 = 4.36 gallons propane per degree of temperature rise. 4.36gal * $3/gal= $13.08 per degree of temperature rise - quite a bit more expensive than natural gas (in Houston).

Scott, thanks for info. Our spa and pool have seperate systems so that the pool can run at the same time the spa is running. We are going to have teen camps and stuff and we wanted both to circulate and run at same time. With this set up, will the pool heat from spillover or would I need a seperate heater?

Use 2 complete pump/filter/heater/chlorination systems. One dedicated to the spa and the other dedicated to the pool. The spa may have a pool system return in it. It should shut if the spa system kicks on.

Scott