Last year we rented a pool home with one of those spas that has the spillover (like a waterfall) into the pool, and it was only heated with the pool water, not on its own. My understanding from researching many pool homes (and I could very well be wrong) is that having the spa heated separately is something that has to be put in separately by the owner when the pool and spa are being installed. I remember seeing some homes specifying that the pool and spa could be heated separately. The next home we are renting has a stand alone hot tub on the pool deck. We have a stand alone hot tub here at home, and the way it stays so hot without costing a fortune is because it has an insulated cover that fits tightly. If a hot spa is important to you, I would definitely ask the owner how hot the spa can get - a real spa is over 100 degress F, usually 104 or so.