Tankless hot water heaters, any opinions.........

Just curious, will be looking to replace my unit and was wondering what the consensus was here. We have two showers, not used at the same time, washer, one outdoor hot water spigot, and a dishwasher. Both the shower units and laundry are on the second floor. Any input is greatly appreciated.
Dave
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This has been discussed extensively here and elsewhere. Search Google Groups for : tankless water heaters You'll get over 800 discussions.
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I have researched this and the one to go with seems like the Bosch (or Tagaki sp? made by bosch). But make sure to get the bigger unit. It seems that people are very happy with that one, but most research I have says they are unhappy with the smaller unit. BTW you can vent those out the side of a house too.

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Ihave a Bosch 117000btu gas it is great for one shower. for 2 you will need the larger 180000 Btu units . Bosch, Talagi and Rinnai. Rinnai is the highest efficency made. You will need a larger gas line for all that BTU. My payback is 4 yrs from switching from electric tank, but my electric costs are 3x that of gas. You dont say if you are Ng or electric or propane. Costs vary over the US. so run your numbers on Btu costs. Im very happy with the Bosch Ng unit
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I have two homes - one in PA and one in FL.
The PA home has an oil furnace that is tankless for hot water. When you turn on a faucet - the furnace goes on and makes hot water for you on demand. It is a bullet proof system and very efficient. It also makes hot water on demand when the baseboard radiators call or heat. the unit is about 2 x 2 x 3 feet.
The FL home has a heat pump and two electric water heaters. The pipe runs are long and you wait forever for the hot water to get to the shower.
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Why do you want to heat hot water?

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so it doesn't cool down...
i have the smaller tk-jr, it runs 2 showers just fine.
-a|ex
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wrote:

We have a gas set up right now bit could actually go either way with a new set up.
Dave
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What is your KWH cost and gas per them. Most of the US has much cheaper Ng. My electric costs are 3x that of gas in the midwest. If you will run 2 showers at any time or have a family the smaller 117000 btu Bosch will not be enough, the 180000 btu Takagi or Rinnai will handle it. Takagi heats to water temp rise so as your water temps get colder in the winter so will output. Rinnai heats to water temp and is 88% efficient vs 83% for Takagi [Takagi makes Bosches large unit] Both have remote thermotats which are a good option, you can put the thermostat in the bathroom. Rinnai I believe has the best warranty. You will need to upsize your gas supply big time , so figure that in first. With electric tankless for a small one shower unit Bosch you need a dedicated 120A circuit-alot of power, Not many have that extra capacity for even a one shower unit.
I have the small Bosch 117000 BTU unit and am completely satisfied. My payback switching from electric is 4 yrs. In summer with gas dryer and cooking all food-Ng my gas bill is 6-7$ a month , Electric was reduced 25-30 a month. Yes the initial cost is high but tanks get reduced efficency every year from Scale-sediment where Tankless remain the same. Also Tanlkess coils should last 3x as long as tanks. It is a worthwhile investment. The Extra 5% efficency of Rinnai vs Takagi and the way it heats to temp, not temp rise as others would make it my choise.
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On Wed, 2 Mar 2005 06:54:35 -0600, snipped-for-privacy@webtv.net (m Ransley) Typed:

The Rinnai 2532FFU is the one I am leaning towards, but if you really want to pump out the hot water I noticed yesterday that Noritz is now offering their Model N-132M, which they say puts out a maximum 380,000 BTU for 13.2 gal a minute at a 45-degree rise in water temp.
<URL:http://www.noritzamerica.com/n132.html
Of course at a $4,000 US sticker price it's a little steep for my budget.
Also, the following was passed along to me by a sales person and you might want to consider it when you look at brands:
Paloma is manufacturer for Rheem and Ruud. Rinnai is manufacturer for Bradford White. Noritz is manufacturer for A.O. Smith/State.
--

Jeff Bailey
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operating as a furnace), I'd go with a tankless gas. Takagi, Bosch, and Rinnai are all good units. If you live up north, be sure to check the flow curves to make sure the unit will put out enough hot water for your worst-case cold water temperature -- most won't put out full flow when input water temperature is below 50F or so.
Personally, I have a Takagi TK-2. It's been a nice unit, and I've never had to worry about "too many loads" -- I've had the washer, dishwasher, and 3-head shower (each head 2.5 gal/min) all going at the same time, and didn't lose any noticeable pressure. Only real downside is that it takes a number of seconds longer to get hot water for a small load (say, a faucet) compared the old tank. Upside, of course, is I can fill the whirlpool tub (or take a l-o-o-o-o-n-g shower), and never run out of hot water.
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Dave Dewar Wrote:

Tankless heaters are the least efficient of all water heating option and the most costly to operate.
They are inefficient because when heated by combustion, far more energ is required to heat the same amount of water as a conventional heate and much of that energy is wasted as excess heat sent up the chimney.
Tankless heaters must always cold water to hot water quickly and canno do it uniformly or cheaply. Tankless heaters, because they do not stor water, must always take cold water and raise it it use poin temperature quickly. This takes a LOT of energy and a lot more energ than maintaining 40-50 gallons at point of use. Since you can in winte need to chrionically heat 32 degrees or colder water that enters you home from outside, because they cannot store water that has alread been warmed, require far more energy than conventional tanks.
Even though electric tankless heaters would be most efficient becaus they do not waste any energy up a chimney, you are still forced to hea extremely cold water and have no way to store water already warmed.
Finally, tankless heaters have a difficult time provide water at constant temperature and one of their greatest drawbacks is not bein able to provide a good steady stream of even temperatured water.
Bottom line is, unless the tankless heater will be for point of use fo a single appliance or used to pre-warm conventional heated water after long distance, they will not help with the bills if you wish to use the for a whole house and with a large family.
Coventional electric water heaters remain the cheapest and mos efficient form of water heating.
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manhatten42 what you wrote is the biggest bunch of bullshit ive seen here in awhile, Yes I own a tankless gas Bosch , that has reduced my bills so much I have a 4 yr payback from switching. Your standard water heater is no more efficient than a tankless. Rinnai tankless are more efficient than most tanks....... 2 other things you forgot, gas tanks do not maintain rated efficiency as tankless do and tankless coils last 3 times longer. Learn about what you write before posting more bad advise
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Your analysis is wrong. Tankless is the most efficient way to heat water for domestic use and saves money.
The tankless have very efficient heat transfer units which imparts the kiinetic energy from the ignition source (Ng, propane or electric) to the water. It takes less energy to raise the temperature of a small quantity of water (heat exchanger) than a larger quantity (storage tank) because of the prinicple of specific latent heat of vaporization. The wasted heat (energy not directly imparted to the water) is minimized and efficiencies of 80-92% are achieved with the proper design.
Oulet water temperature is monitored and regulated. If the output temperature falls below a preset or the temperature differential between the inlet water and output water temperatures exceed the design limits of the unit, the water flow is restricted. This allows more time for the kinetic energy from the ignition source to be imparted to the water, maintaining the water temperature.
Storage tank systems heat the water continuously 24x7. Energy is wasted as heat loss to the surrounding atmosphere because the insulation on the storage tank is not 100% efficient. When the demand on the water is great enough to depleat the hot water in the tank, the water temperature drops. It takes an enormous amount of energy to reheat the water after the demand is removed. The large mass of water has a constant heat absorbtion rate and a temperature differential.
mass of water x specific heat capacity x temperature change
is the formula to calculate how much energy must be imparted to the water to raise it temperature from start to boiling. A large quantity and large differential will require a large input of energy. Very expensive in term of Ng or electricity prices.
Other things to think about. If you are the type not to repair leaky valves, then you waste water AND energy if you have a storage tank system because you discard hot water. If you have a tankless system, you only waste water because the flow rate of a leak is not enough to trigger the heating process.
On Tue, 1 Mar 2005 11:40:58 -0600, manhattan42

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much difference? Also, is there anything specific that we need to look for in a tankless? B
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I recently switched my 28 year old storage tank water heater for a tankless Rinnai unit. A replacement tank would have cost $1500; the Rinnai cost twice that. Installation costs would have been the same. The savings I can't say exactly but I suspect that they will be significant. I estimate that I will pay back my costs within three years through Ng savings.
What I looked for was efficiency (energy in to energy out ratio) of around 90% or better. The Rinnai gives me 92% I believe. I also looked for reliability of mechanics. Rinnai is tops here as well. The third factor I looked at was the installer. I regarded three installers and picked one that had a history of good customer relationships and dependable service history.
I evaluated one other feature that swayed my choice to a Rinnai. The Rinnai I bought is a combo unit which means I can use it to heat the house as well as serving my domestic hot water needs. The installer will replace the Ng burner in my furnace with a heat exchanger unit attached to the Rinnai, leaving the air filter and blower unit intact. The Rinnai will heat the water to 180 degrees F and circulate that through the heat exchanger in a closed loop. My furnace is 78% efficient, the Rinnai 92%. I will save additional money through reduced Ng consumption. I'm not sure the efficiencies of the heat exchanger in the furnace core but I suspect it is very high.
When I researched I found a few articles helpful on the web: http://www.joneakes.com/ca/hs/cgi-bin/getdetailscahs.cgi?id 47 http://www.tanklesswaterheaterscanada.com/takagivstank.html
wrote:

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manhattan42 wrote:

Incorrect.
Incorrect. It takes 1 BTU to raise 1 pound of water by 1 degree F regardless of what heater is doing it. Simple physics. But tank heaters send more heat up the chimney.
<snip>

That guy used bad math. He assumed that the tankless heater would use 168,000 BTU/hr regardless of how much water was being drawn through it. He has no basis for that assumption and he certainly did not measure it. His bad calculations are outof line with others' direct experience.
One caution here, it is important to distinguish between a tankless water heater which is specialized for domestic hot water vs. a tankless water heating coil which is an add-on for the home heating system boiler. The latter is cheap but not particularly efficient.
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