What’s the best heater if I want to maintain a constant “warm” temperature in the pool?

For those clients who are going to keep the pool at a desired temperature all year, a heat pump is the best way to heat. There is no such thing as inexpensive heat but the heat pump will do the job most efficiently. It can literally pay for itself depending upon the owners’ temperature “demands”. Asking a gas heater to perform in this same way, especially the standard efficiency heaters, is far more expensive.