Can an external gas heater be added to my existing spa and what are the benefits?
In many cases the answer is yes. You will have to splice some intake and return plumbing from your spa to the external heater. Heater installation must be done in accordance to local building code requirements with regard to plumbing, gas lines, electrical connections (if needed), distance from spa, venting, heat sinks, etc. But setup is usually not terribly difficult. Instructions are supplied with the heating units, which are available in either natural gas or propane models. The benefits include reduced heating costs, which will help pay for the heater over time, and much quicker heating time.
