Redneck,

The newer models have no problem filling a large tank with hot water, much less a bathtub. We have done this on several occasions.

Tex_n_cal, we have the types mounted on an outside wall and plumbed into the house instead of having the unit indoors.

They DO require a 3/4" gas line instead of a smaller line, and the temperature CAN be raised beyond 120F. There is a sequence of operation to allow this, but the water heater MUST NOT be operating to do it, and you can go to at least 140F with them. They are set with a default 120F to prevent scalding.

The smaller units come with thermocouples preset to certain temps and you just install the one that you want, the larger units can be changed via the keypad.

Ed

How far from the bathroom was the heater? If not right in the bathroom, it takes time for the hot water to get through the pipes.

We just replaced our 1975 boiler and 1995 water heater (both gas) with a new high-efficiency boiler and side-arm water heater. The water heater is only a 40-gal unit, but it gives us more hot water at the tap than the old 50-gal stand alone unit did.

The tank temperature on the new water heater is held at 160 degrees and the outgoing water goes through a mixing valve that drops it to our desired setting. This makes the tank of hot water go a lot further than its 40-gallon capacity suggests. We can also add a programable thermostat to the water heater, to further reduce our gas consumption by letting the water tank cool down during periods of low demand. We haven't done that yet, though.

We're really happy with the new setup, and we've noticed that we no longer have to adjust the water temp while taking a shower. The shower temp stays pretty constant now, and we don't run out of hot water while the showers and washing machine (or dishwasher) are running at the same time.

We debated about putting in an on-demand water heater, but we got too many mixed reviews from people that had them. Of the folks we talked to, some loved them and others hated them. Everyone that had a side-arm water heater/boiler setup raved about it, though, so we went that route.

Water is expensive to heat. Usually it's the most expensive energy use in the house. Why would you heat it hotter than you need just so you can cool it down to use it? I think you'd save money by not heating it any hotter than your max use, like 120 to 130.

This is just a guess but it sounds to me like they do this to make more hot water.

Another vote for the Eternal hybrid gas unit. It has a small (two-gallon) tank that it keeps hot; that eliminates any "lag" when you turn on the tap. By the time that's gone, the unit can keep up. We have ours set at 130° and for a hot shower, the mix valve in the shower is right in the middle. We bought the unit sized for a family of four, with a thought to eventual sale of the house. We can run two showers and the dishwasher at the same time with no loss of hot water.

Cost to run? Our natural gas bill since we installed it in February has been $12 a month. The estimated cost sticker on the side of the unit says it will run for $192 a year and so far, we're a good bit under that. It has a 20-year full warranty.

I'll never consider having anything else.

Very good to know.. Thanks for the update..

I had a plumber give me an estimate on a Rinai 2 years ago when our Heater went south. The only reason I did not buy it was the very expensive insulated tubing that would have to be ducted thru our roof from the garage otherwise it was a done deal.

January last year, I had a Rinnai RV53 installed. I am very happy with it. Yeah, it takes a few moments to get the hot water to the tap, but after that, it just runs and runs.

I don't know about the other mfg's, but Takagi was highly recommended to me by the folks I bought my Pex and circulators from, and I'm using one of their largest tankless propane-fired units to heat the concrete floor in a 2800 square foot shop. I raised the default temp to its max via dipswitches on the PC board.
I see no reason why these couldn't handle all the needs of a residence; they're pretty awesome units.