Ok, I'll be the oddball.
We went with the Isotemp Spa 40 (11 gal) on NWD. At the time what interested me was the bulkhead mounting options, 316 stainless tank, plastic (non corroding) exterior shell with good foam insulation, included mixing valve and factory installed 750w heating element.
I wanted to mount the water heater in some basically useless (for anything else) space between one end of our generator and a fuel tank enclosure, but it would need to be high up so as to keep access to a couple through hulls easy. A tank such as the ISO Spa would allow this mounting - horizontal on a bulkhead. It DOES mount vertically, but only on a bulkhead with the fittings down. The instructions say it can't be mounted "fittings up" for some reason. Possible disadvantage for the OP.
The exterior shell just makes sense to me as its one less thing to corrode. It basically has to support the mounts and enclose the foam insulation, so I think its suited to its purpose. We routinely see hot water suitable for showers a full 24 hrs later here in the PNW. Our engine room typically stays around 60 degrees or less once the engine heat has dissipated - up to 70 degrees if its hot and sunny out.
We do go through hot water a lot faster than I'd like, but I think the biggest problem with that is a LONG copper pipe run through the bilge area, so there's a lot of wasted water waiting for the hot to get to the shower, then a lot of heat loss through the copper pipe along the way - its not insulated. An upcoming major project will be new freshwater plumbing throughout, and I'm thinking PEX might hold heat a little better. The other problem is the Admiral and I are not as efficient in taking Navy showers as we could be...
The included mixing valve is a very nice feature; saving me from having to buy separate. The port engine heats the water up past 165 or so, and the heater is set to 160 F, so having the mixing valve is both safe and helps extend the water (having it way hot then mixing with cold makes it go farther.)
One feature I am second guessing is the heating element wattage. I originally wanted the 750W element to help keep from overloading our generator - charging batteries full bore plus heating water full bore (many other hot water heaters in the 11 gal range use 1200-1500 watt elements.) As it turns out, my 7.5 Onan has more than enough umph to do both the higher wattage element and our Magnum battery charger even when on full bulk charging. ISO has the 1500 watt element as an option, and I'm thinking of swapping to it. If we have run the hot water all the way down near ambient, it would take 3 1/2 - 4 hrs to get it fully heated. (calculate the BTU required to raise 11 gal from 70 or 75 to 160 degrees, then how long it takes to get that many BTU's at 750 watts....) I will almost* only ever let it run until the batteries are getting past the point of efficient charging with the generator, so maybe 2 to 2 1/2 hours max in a day.
(* I admit to running the genny only to make hot water a few times, after it was all inadvertently used or the breaker off
when the genny was running for the batteries. The Admiral WILL have showers on board, and they WILL NOT be cold ones. Aye Aye ma'am!
)
If you will find yourself making hot water on the generator, consider making sure whichever heater you choose has the heating element to support it in a way that works for your AC power availability.
I can make no claims about its long term life, as I've only had it for two years now. In my reading of reviews (in Practical Sailor and looking for issues in forums) I didn't find anything that led me to believe its short lifespan heater. It has the same warranty (5 yrs) as Torrid. The price was very reasonable, I want to say under $600 before tax.
All that said, I am somewhat ashamed for not buying the locally make Torrid, it goes against a lot of what I try to practice for doing business with good local trades and other businesses.
