I bought one of these 2 years ago. It's wonderful. Been running like a champ since then. I even have it partially exposed wind and rain (dumb) and it's been fine
(I really need to build a little roof over it, but right now it's just protected by the eve of my house, not directly facing the wind but it gets glanced)

This is why i STRONGLY support this product. I personally don't trust a lot of 5-star ratings on Amazon cause they sound fake, but I'm an actual person who owns this water heater.

The only con about this water heater is that i don't get enough pressure in my water line to be able to adjust the water in the shower by mixing cold water with the hot, i have to actually adjust the amount of gas flow (the left knob) to adjust the water temp while showering. If i try to run cold water while the heater is trying to get enough water to function, it shuts off. Maybe you'll have enough water supply for the demand. I think my neighbor, the guy i get the water from, has a pressure reducing regulator at the source because he's afraid of the line bursting or getting holes from too much pressure.

So to make up for this minor inconvenience, glued a plastic-coated steel wire around the knob (only tacked to it with wire going partially around top and bottom like a pulley), so in the shower you pull either the top or bottom string to adjust hot/cold. (The shower and water heater and lined up side by side but at a distance)
I recently bought another one of these for my guest cabin and since it's under an enclosure, i just made a hole in the privacy divide where the person can reach through and turn the knob by hand. Much easier. Again, this is mounted outside, but this time with a roof overhead and 3 walls.

When i first bought this thing i didn't have the right pressure regulator for the propane tank. I had one for gas grills that was way too much pressure, but other ones for gas grills are actually low pressure. You need a low pressure one. I think this unit needs less than 1/4psi, max i think 1/2psi or something. You gotta read it in the manual. So i called Eccotemp. They're a small outfit but EXTREMELY HELPFUL, and we eventually figured out why i was getting a E3 error reading having to do with the gas. They offered to send me a new computer or something and sounded like they were going to do it right away. But i got the engineer or someone's e-mail and he informed me about the pressure since i had mentioned bbq grill etc.

All in all, this thing rocks!!!

Wanted to wait a while until offering a review on this water heater. It's been in my 29' travel trailer for about 3 months now. It installed very easily. I suppose I understand why it's not recommended for MY use, but, then again, I also understand how sue happy people can be over the stupidest things. That said, I am VERY happy with how this little beauty performs. Getting the water temperature right can be a bit fussy and take half a dozen uses before you get it dialed in, but it excels at delivering unlimited hot water in about 5 seconds to the furthest part of my trailer, and the shower is nearly instant (mounted in the bedroom next to the shower). It appears to "sip" propane, and doesn't intrude into the limited space one has in a travel trailer. Heat from the unit is NOT an issue. I can nearly hold my hand on the vent pipe when it's running, and it does not get hot enough to ignite anything due to the power venting. It's very quiet, ignites instantly when it senses water flow. The fan continues to run for 5 or 10 seconds after the flame is stopped.

If it holds up as well as it performs, it's an absolute winner in my book.

Should I encounter any issues, I'll update this review.

UPDATE: Still deserves 5 stars. It amazes me how little propane it uses. I started with a full 20 gal tank and STILL have about 3/4 of it remaining. During the warm weather, I had to lower both settings to account for the warmer water coming into the unit, which is really easy.

UPDATE 7/7/17: Still super happy with this water heater and have had absolutely NO issues with it. Use it daily all year long and am STILL amazed at the way it sips propane but heats water well. The super easy adjustments make it easy to vary the temperature even day to day if needed. Would happily recommend this unit!

Hooked righjt and is heating water

My husband used this for his deer camp & it is perfect & exactly what he needed!

I installed the FVI-12 to replace a 40 gallon, propane fired, power-vented, tank unit. The heater I replaced was very similar to this one: American Water Heaters PVG62-40T42-NV Residential Gas PowerFlex Direct Vent Water Heater, 40 Gallon . So far we are very pleased with the Eccotemp FVI-12.

Usage Patterns

A tank storage or batch heater like the powerflex is very good at supplying a lot of hot water all at once, while a small tankless like the FVI-12 excels at providing a smaller amount of hot water more or less indefinitely. Most of the decision is in matching the tool to the job. In our case, we are family of 4 who take showers sequentially and other usage occurs later in the day. This matches the tankless pattern well. If we had multiple simultaneous uses we'd probably be less pleased.

Installation

I installed the Eccotemp in the same location as our old water heater. The gas line was the same and required no modification at all. The water lines were a different size and, because the FVI-12 is smaller and hangs on the wall, they needed to be longer and end in a different place. All of that was relatively easy and inexpensive, about $40 in fittings etc.

Venting turned out to be the most challenging part of the installation. The old heater used a 4" PVC vent pipe which allows for zero clearance to combustible materials. The FVI-12 uses 2-1/4" stainless vent pipe which needs much greater clearances. A discussion with Eccotemp tech support led me to enclose the exhaust vent in a 3" single walled vent pipe in order to decrease the clearance to a PVC drain pipe. So far this works beautifully, and the outside shell doesn't even get warm to the touch when the water heater is operating.

Due to the location and the thickness of the wall I needed a longer vent pipe (The FVI-12 includes about 13" of vent and an elbow). (One of the short-comings of the manual is that it doesn't mention the maximum vent run, which is 17 feet according to Eccotemp tech support). Unfortunately the proper 2-1/4" stainless thin-walled tubing is hard to come by and, at the time I needed it, back-ordered. A friend who owns a local muffler shop came to the rescue with an inexpensive exhaust pipe cut and formed to the exact specifications needed. I would recommend this approach strongly, except that stainless wasn't available so I have doubts about durability. I'll be monitoring the condition of the pipe very closely.

Documentation and Function

I found the manual to be better than average but it definitely had room for improvement. As mentioned above, it doesn't include the information about the maximum vent length and it leaves several other matters ambiguous. The manual is available as a download from the Eccotemp website which makes it an easy matter to form your own opinion of it before purchase and does give a pretty good idea of what is involved in the install. There are several typos.

The device has only two controls and an LED display. The display shows current water temperature and any error messages. The knob on the left controls gas flow, the knob on the right is labeled "water temperature" but *appears* to control water flow rate. Adjusting the temperature setting is a matter of turning on the hot water and then adjusting these two knobs until the temperature stabilizes where you want it. The manual suggests starting with the gas all the way down and the water all the way up. The FVI-12 does not appear to have a thermostat but I could be mistaken in this, perhaps its operation is subtle.

Technical Support

Eccotemp technical support needs its own category because it really is in a league by itself. I was pleased and amazed when they called me back on a Saturday morning over a holiday weekend. They were polite, customer service focused, and technically knowledgeable. Good technical support goes a long way toward making up the short-comings of the manual.

Conclusion

So far, after the installation and about two weeks of usage, I'm very pleased with the Eccotemp FVI-12. It works better for us than our old water heater at about 30% of the cost. It worked right out of the box the first time, and included everything which would have been needed for a typical installation. The manual was tolerable and the technical support is first rate. I give it four stars instead of five due to the short-comings of the manual and the somewhat awkward controls. Fixing the manual and providing true thermostatic control (or a better interface) would make this device a complete winner. My last remaining concern is durability, and given its appearance, I have high hopes, but at 30% of the cost of the alternative I'd still consider it an excellent value if it lasts only half as long.

Pros:

Excellent Tech Support
Tremendous value for the money

Cons:

Manual needs a little work
Not suitable for multiple simultaneous use or (as noted elsewhere) low water pressure