I believe there's a new standard that came out a few years ago and most that I've looked at are 83% or a tad over. There is one model that's a lot higher but also 3x the cost. Raypak has a firebox design that's a little different. Uses traditional burners at the bottom with tube sections in the box above the burners. Many others seem to use a concentric firebox with a burner tube in the center that fires down and out with tubes that circle around it. All that I've read manuals on use electronic flame sense technology instead of the old thermocouple which is safer and claims to be more reliable. It also seems to be a little more problematic for pool heaters maybe because it is very sensitive to corrosion in the grounding system. There are a lot of posts about this and it's not really that hard to fix if diagnosed properly. There are also some nuances in the details like negative pressure gas system, separate flame sense rod or combined flame sense/igniter. But they all seem to work well and have about the same amount of maintenance required. I have a Jandy Jxi and I learned way more about it than I ever wanted to about it when dealing with a lightning strike that wiped out a lot of my pool equipment. I was able to fix it with a lot of help from experts here and determination to figure it out myself. Now that I understand much more about how they're built I really think the key to long reliable life is more about maintenance, water chemistry, and proper installation than brand. A standard design heater is about $2500-$3000 and the most expensive part is the tube bundle that's about $800. A few other parts are $300 each and the rest are pretty cheap sensors. Fortunately sensors are the most common failure and very easy to diagnose. So it's not really that hard to keep any brand running a LONG time for a capable DIYer. Or have access to real good repair service that actually knows what their doing and can actually diagnose rather than trial and error it.
My $.02.
Chris
