Hello and welcome to my first post.
I own a pool spa combo. I heat the pool with a solar heater and am very happy with doing so. The spa on the other hand is in need of a new heater. The heater i currently have is a gas guzzling dinosaur that is on its last legs. Its large enough to heat the pool and then some. I am looking to replace it but with something much smaller, because i am only interested in heating the spa with it. Is this something that is commonly done and if so a little guidance in the right direction and a suggestion on an actual unit would be much appreciated. The spa is approximately 500 gallons. Thanks for any help you guys can give me.