In a jetted tub I usually think it's awesome for about 5 minutes, then I turn them off. I can't really put my finger on why but I just don't care for it after a few minutes. The option would be nice for visitors who do enjoy it though.
A lot of the salvage tub is no good. It wasn't heating and they couldn't fix it, or determined it wasn't worthwhile to fix it anyway. I guess I could get lucky and find it was something simple though. I'm expecting to find that it won't help me with heating but surely there are other parts I can strip that may be of use. Or I may want to use some day.
If you think 4k watts will maintain heat in 700 gallons while open I'll give that some consideration for sure. Either one more 2k in series or one 4k or so 240v heater. Electrically doesn't efficiency diminish with 240v, or do I have that backwards?
With just 2k watts Sunday we had it open a little over 3 hours and lost about 5.5 degrees. Ambient temps about 40. We were all still comfortable and enjoying it when we got out to eat. I'd say right now 3 hours is our threshold for needing more.
I already have the 18l (5gpm) propane heater for open use. I just have to install it.
For now I think I'll pause there and focus on insulation for the next little bit. I want to get some good baseline data for how much heat it loses while off now, so I can see the effectiveness of my next round of efforts.
Duke Energy has an app that lets me see the energy use out there at the pool house. I can see by day, week, billing period, and even per hour. That makes it easy to track changes and improvements.
With an ozonator, I see how they work, and see how easy they make it on this site, but I'm not sure about what it takes to add. I'm not certain whether it's something easy to add as a standalone product in an application like this or if they are more something that's usually built in and on the hot tub controller and more complicated. And I need to learn what size I need, etc. I'm guessing it would lower chlorine levels and help me reduce the corrosion due to chlorine over time and extend the life of the tank also?