I for one always like gas over electric. Storms rarely affect gas lines so you can always have gas such as for your stovetop or house water heater. Obviously with a pool you also need to have electric to run your pump so gas or electric pool heater is a mute point. Does your spec show which is more efficient?
Propane consumption is truly dependent on use of heater. If you only heat your spa then that will extend the time to refill propane. If you heat your pool that is a different story. My heater states it could take +12 hrs to raise temperature 30 degs for 14,000 gals.
I had a pool heater that lasted 14 years - had some maintenance occasionally but finally purchased a new one recently 400BTU.
Your heater specifications should outline how time to raise the water x degrees. For instance, my heater states it will raise the temperature 30 deg in 31 mins for a spa with 700 gals. Check your heater specifications
It is fairly standard on your return line (after the heater) that it can split to either the pool or to the spa. This is controlled by a valve and that valve can be controlled by your RS8. This is part of your standard plumbing for circulation.
On mine, when in pool mode, I have 1 jet that enters the spa to spill over into the pool So in theory I could heat both the spa and pool at the same time, however the pool has 5 returns so majority of flow is going to the pool.
Hope this helps.
