I would post this in the plumbing forum, and do some searchers there.

Myself, I don't think they are ready for "prime time " yet.

One of the more common posts you will see about the on-demand gas water heaters is you have to set them for the shower temp that you want, If you set higher, for example 120 F or so (for say like a dishwasher), then the shower will get hot and cold, as the heater does not see enough Hot water demand, so if you turn the shower down the shower gets hot and cold---don't take my word for it, check the posts over there.

They are making recirulating systems now that have to be added, but that's extra money and to me, not worth it.

Do some research on some of the newer condensing tank water heaters, and pilotless (assuming you are looking into a gas water heater).

If old one is > 8 years old, I would just replace it, if less, maybe it just needs a new control.

Gary

I looked into it for our house. I really wanted one.
We live in the upper Midwest.
Check your delta temperature. This is the water temp coming into the house vs the hot water desired temp.
Our water is 37 degrees in the winter. We would have needed an industrial model for our house and the costs outweighed the benefits. Plus, I wanted the on demand so I could have quick hot water- but it still needs to get from the device to the location plus heat the water.
Our solution- Smith Vertex (I think that was the name) It is classified as a high efficiency "hybrid".
We have been using it for 5-7 years and have been very satisfied.

We replaced the aging water heaters in our home just over a year ago. The plumbers working on the job were very keen on Rinnai, so I spent a lot of time reading up on performance, cost, etc. Bottom line: with luck, you might break even, i.e. get the same performance for the same cost, after about 15 years. But most people think that overall tankless systems are still too expensive, and the costs remain higher than traditional tanked systems even if the tankless heaters work exactly as advertised.

The main advantage is if you have a high demand for hot water at specific times. So if you have a houseful of guests who all take showers at 7am, tankless ensures you don't run out and have to wait. Friends of ours installed tankless water system for just this reason.

Note that with tankless, you can sometimes wait for a couple of minutes for hot water to reach your faucet or shower. Our friends installed a small electric water heater to avoid this.

We went with conventional water heaters this time around. In 10 years things may be different.

Cheryl

I've had my Rinnai for almost 3 years and love it. It immediately cut my gas bill in half (from about $34 per summer month to $17). I never worry about running out of hot water or a pilot light blowing out. Mine is set to the maximum 120 degrees, which is OK because my dishwasher has its own water heater. Never again planning showers around laundry and dishwashing?=priceless. The only downside is the 60 seconds of cold water from the hot tap until the heated water makes it through the pipes.