Tankless water heaters

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Does anyone have experience with tnakless water heaters?
Are they really cheaper than a central water tank?
Do I need one installed next to every hot water tap?
What is the cost (roughly)?
Any detractors?
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On 11/9/2010 5:01 PM, Prof Wonmug wrote:

I've never had a water heater tank me, they are all selfish and very rude. 8-)
TDD
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wrote:

The ones I've seen installed were in new construction. The owner loves them; three units in a 5000 sq ft house that are on separate zones. His were mounted outside the home (in stucco) located in the desert.
Have a look at this buying guide.
http://www.tanklesswaterheaterguide.com /
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water heaters, one for each floor. She loves them. Very little wait for hot water to reach a particular location and water is only heated when needed.
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"ELGY" <lgpetersatcomcastdotnet> wrote in message

Each cup of tea represents an imaginary voyage. ~Catherine Douzel
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Ala wrote:

I use Stiebel-Eltron mini point of use tankless water heaters when my wood boiler is not running. They work great and take 25 amps when running or drawing hot water. One under the kitchen sink and one under the bathroom sink/bath/shower. They work great since I don't use very much hot water; just a shower once a day and some dishes. Take no more than a toaster. The only detractor is if the power goes out, no hot water. Had it happen once while in the shower. Instant cold water. They are still about $150 each. Had mine for 4 years. If you have a really cold cellar you might need 2 in series for really hot water.
--
LSMFT

Simple job, assist the assistant of the physicist.
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i'm glad you are happy
i felt the way you do when i first started the project
i feel lost again that i moved but know that i am not where i need to be
start collecting gossip about what folks are saying about the device
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On Tue, 9 Nov 2010 16:05:14 -0800, "ELGY" <lgpetersatcomcastdotnet> wrote:

Do you know what brand?
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On 11/9/2010 3:01 PM Prof Wonmug spake thus:

Yes.
Yes. And no. (See below.)

No.
If you're talking about the cost of the heater itself, a lot more than a tank-type heater.

Yes. And no.
(This subject has been discussed extensively here in the past; you might do well to browse some old threads here.)
The problem with tankless (aka "demand" or "on demand") water heaters is that they were overhyped, back in the 19-ought-70s, to be the do-all and end-all in efficiency and conserving energy.
Turns out that they *can* conserve energy, in some situations, depending on several factors. However, they can also *increase* your energy consumption in some cases.
Best to go back to basics: how do they work? (It's surprising how many folks talk about them without really knowing this, so it seems useful to go over this here.)
A regular tank-type heater heats a large volume (10-40 gallons) of water with a relatively small burner that uses a relatively small amount of gas. It keeps that tank at the temperature set on the thermostat, so it uses this small amount of gas periodically as the water is used, and as the water cools in the tank.
A tankless heater has no tank, as you'd expect. Instead, it uses a heat exchanger--basically a radiator in reverse--over a burner which uses a *lot* of gas. A *lot*. But it only heats the water as it's being used; the flame goes on when water is drawn (i.e., when someone opens a hot water faucet), hence the "demand" part. When no hot water is being used, no gas is used at all. (Newer tankless heaters use electronic ignition, so no pilot light.)
The thing is, the tankless heater can save you money on gas, but it depends on a couple factors:
o The distance from the heater to the farthest hot water outlet o The usage patterns of the household
The latter one is the most important. I'm not an expert in this field, but it seems obvioous to me, at least, that if a household uses a lot of hot water throughout the day--say, doing a lot of laundry plus hot showers--then a tankless heater could actually end up costing more. Why? Because in order to heat the same amount of water as in a water heater tank, the tankless heater is going to use a lot more gas.
It'd be nice if there was some clear explanation of this out there in Web-land, maybe even some kind of online calculator or something. But the moral of the story is, you need to do some investigation, look at your water usage patterns closely, and don't get sucked in by hype about tankless heaters (either pro or con).
That's my story and I'm sticking to it.
--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.
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What is your basis for the above? It would seem to me that both a tank heater as well as tankless are going to get about the same amount of heat out of a given amount of gas that goes in. The tankless just uses a lot of gas or electric over a short period of time, while the tank type uses less over a longer time. If anything, I would suspect that a tankless is more efficient compared to a std efficiency tank water heater. The main energy savings AFAIK, comes from the elimination of the standby losses from a tank type heater. Whether that savings is enough to pay for the cost difference, including install, is questionable.
And I fail to see what relevancy the usage patterns have, at least with a typical whole house unit. If I use X gallons of hot water, what difference does it make when I use it, unless the point here is that with electric units there could be a time of day difference in rates for some? With a typical whole house unit installed somewhere, you're going to have piping losses with either type. And if you put in mutiple tankless to cut down the delay time for hot water, I would think the increased cost would take so long to recover you may never come out ahead.
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On 11/10/2010 5:53 AM snipped-for-privacy@optonline.net spake thus:

Well, like I said, it was a guess on my part, hopefully an educated one. Your take is just as plausible; my point is that we really don't know, do we?
Here's one argument in favor of my thesis:
Consider the most ridiculous case possible, someone who only uses hot water once a day, say to wash their hands. In such a case, a tankless heater will fire up exactly once, while a tank heater will fire up several times during the day to maintain the tank's temperature. So it seems likely that a tankless heater could save fuel in such a case.
Now consider the opposite case: someone who runs hot water all day long for some strange reason. In such a case, both a tankless heater and a tank heater will be burning fuel all the time. The main difference here between them is the size of the burner: the tankless burner is a lot larger (think your oven's burner as compared to the tank heaters's stovetop burner). So again it seems likely that in such a case a tankless heater could use more gas for the equivalent usage. (Of course, the other difference is that the tank heater will eventually stop putting out hot water, unlike the tankless.)
So it seems likely that one could construct some kind of crude curve of comparative fuel costs vs. water usage.
But I don't know for sure. It's sure be nice to have some better information on the subject.
--
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with the flaunting of well-defined muscle, wrapped in flags.
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Tankless coils are big enough to extract as much energy as possible, there are several Condensing tankless made that get 94-96 EF the exhaust is about 70f. The best tank is mabe 86 EF. . Its true tankless for a big family makes less sence. For many commercial uses it makes no sence when you figure that tankless cost many x more.
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I think if you go to any independent, credible source on tankless, eg DOE, they in fact say they are more efficient than tank type and they don't give caveats like yours about them becoming less efficient if you use water frequently throughout the day. In fact, that is precisely what tankless are good for, supplying continous hot water without ever running out.

What you're missing here is a couple of things. First, the efficiency of the unit is what determines how much hot water you get out for a given amount of gas or electricity that goes in. Whether it uses a smaller burner over a longer time or a larger one over a shorter time, doesn't matter. Second, the tank type heater has basicly the same standby loss whether it's used once a day or frequently throughout the day. Just because it's already running due to hot water having been drawn and consequently you don't notice the burner starting up due to standby losses, doesn't mean they disappear. Heat is still continually escaping from the tank.

If there was a need for such a curve, don't you think we'd have one by now?

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On Nov 10, 7:53am, snipped-for-privacy@optonline.net wrote:

This isnt easy to explain but its what ive read and how I see it. If a tank is in heavy or constant use it makes a difference. A tankless for one or 2 will be run a few times a day, it uses energy and thats it, its off. A tank for one or 2 maintains that temp all day but so here is where a tankless pays back quickest. If a tank is in heavy near constant use since both systems burners are equaly efficient a tankless saves less in relation to a heavily used tank, the tank has less downtime where its not needed.
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Near the end of a generally good discussion ...
On Tue, 09 Nov 2010 16:06:31 -0800, David Nebenzahl

No. Physics 101 is your friend. ;-) Burning a given amount of methane releases the same amount of energy no matter how fast you burn it, assuming complete burning. Raising the temperature of a given amount of water the same number of degrees requires the same energy input no matter how fast you do it.
Possibly what's confusing you is that the tank heater burned slowly for a long time to heat the water, while the tankless heater burned fast for a short time. But at the same efficiency, they used the same amount of energy (gas or electric). And tank and tankless efficiencies overlap, so one or the other could be more efficient.

Your last (parenthesized) statement is not the "other difference". It's the critical difference. You have hypothesized a comparison between running hot water all day long and running barely lukewarm water all day long. Not surprisingly, running how water requires more energy than running lukewarm water.
If you change your comparison so that the experiment ends when the tank heater runs out of hot water, then both use the same amount of energy. Only the pattern of use is different: the tank heater used the energy before you started running the hot water, and the tankless used it while you were running the hot water.
Edward
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the new condensing water heaters qualify for the fed tax rebate, they are over 90% efficent......
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From what I understand, adding a tankless system in a new construction will provide payback in savings. Adding to an existing home will pay back in 15 to 20 years (or more), depending on usage. It is not recommended to add to an existing home. Chances are you'll sell the home before you gain what you paid.
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Actually, a retrofit is viable if the OP has proper sizing for water/gas/electrical (which need).
We just don't know if he is comparing pomegranates to persimmons.
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Even that is doubtful. You have to add the increased cost of the unit itself, the increased cost of installation (including larger electric or gas service), and required annual maintenance. The operating costs for energy can be higher as your rate is often dependent on the size of the service.
Storage tank heaters are far more efficient than people realize. There are specific circumstances where demand heaters make sense, but economics aren't usually the reason.
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Yes. I investigated them. The upside is that they will cut your costs. The downside is that the large ones require a high amperage feed, hence big lines and breakers, and the water that comes out is only so hot. The cost of running electricity to every supply can be done if you are in the construction phase without as much cost as a retrofit.
I have no idea about the propane ones, but imagine with the cost of propane and natural gas going up, that their operational costs may be high.
Let's hear more from people who actually have them. I just checked into the ups and downs of getting one, and my electrical feed was insufficient, the cost to upgrade was high, so that was that.
Steve
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