HOT WATER ON DEMAND, HEATERS

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Since you want to use Wikipedia and I dont know how to paste look up Condensing boilers, you will find what I said is true that 98% is the highest claimed for Condensing boilers, but also that figure is optimistic, a bit high, and a reduction of 4-5% is more realistic or real world performance. That makes condensing boilers about 93% efficient Maximum.
By SEDBUK this gives Condensing boilers a typical seanonal efficiency of 82-89% HHV.
I quote Wikipedia
""When installed in real houses, the performance of condensing boilers is typicaly 4-5% lower than in laboratory tests by groups such as SEDBUK . This gives the typical seasonal efficiencies of 82-89% in the UK [ HHV ]. ""
< This is your testing done by your SEDBUK, we in the US have the same ceritified Gav standardised testing and sind same results, end use results are less optimistic than advertised by manufacturers and probably put units condensing units around 90%, you just dont get more Btus out than you put in.>
You do if you siphon off that energy from a source other than the direct combustion of fuel. Fuel and air are burned at room temperature. That is usually around 70F. Inlet cooling water is around 40F. The cooling of the exhaust below room temperature allows the boiler to extract the energy of water vapor that's a byproduct of combustion by causing more of it to condense than it would at room temperature. The cooler- than-room-temperature exhaust of a process that's burning gas is a big clue that it's not a typical combustion process and something extraordinary is going on. How many engines or combustion processes do you know that have not just a cool, but a cold tailpipe?
The phase change energy of condensation plays a key role. If your exhaust energy is reclaimed and exits below room temperature, you've captured and reclaimed the thermal energy stored not only from fuel combustion, but also the heat both fuel and air bring into the process just having mass. A cool exhaust from a combustion process *has* to mean that both the waste heat that would normal go up the flue and the energy it took to warm the fuel/air to room temperature is recaptured and extracted. How else could there be a colder than room temperature exhaust product by combustion? The laws of thermodynamics are scrupulously obeyed and no energy is created, it's merely scavanged from a source other than direct combustion. The BTU's used to heat the air and fuel to room temperature are recovered and not sent up the flue. That sort of energy scavenging is not accounted for in typical efficiency calculations.
The key is that the energy is extracted from the fuel in different ways: from its thermal mass, from the heat from its combustion and by the energy that comes from water changing phase from a vapor to a liquid. Lower the exhaust below room temperature and you've extracted close to "free" energy (it's not really free since someone paid to heat the air and fuel in the first place). It's a pretty remarkable process. Is saying 101% efficient a gimmick meant to grab people's attention? U-Betcha (wink, wink!) There are so many way to slice and dice data, I'd want an asterisk next to that number, but in terms of squeezing every last BTU out of fuel, including recovering the energy that it took to raise it to room temperature, it's pretty slick.
-- Bobby G.
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I don't know what you consider "very low", but here in the northeast they sure don't meet my definition of that.

I'd say that depends a lot on whether the tank is high efficiency or not. With a conventional flue system, as Ransley pointed out, most of the lost heat goes up the flue, not into the house.

There is however very likely enough water present in the tankless to absorb most of the heat after the burner shuts off. Or else it would boil, which apparently it does not.

I'm sure most of us here would like to see any credible source to back up this analysis. First, just about all of us agree that for the typical residential usage, most of the energy in either type water heater goes to heating water that is actually used, as opposed to being lost. So, if tankless really only converted 50% of the gas used into heated water, while a tank converted 80%, why would DOE and similar organizations be recommending tankless to save energy? Also, what are the efficiency rating numbers all about? Why don't we see what you claim reflected in the efficiency ratings?

I'd like to see a credible source to back up this claim too. As for their having "control devices, electronics, etc that are not present in conventional heaters, while they may have different devices, it hardly seems that they differ significantly in complexity from a direct vent tank type water heater.

I believe there are some tankless that have battery power.

Again, I'd like to see a source, besides your own opinion, that makes this case. I think in most cases, it can take more than a few years, perhaps even ten years. But it obviously depends on the particular circumstances. Ransley bought his for $500 and installed it himself. At the other extreme, you could have situations where it requires increasing the gas service size, significant new piping runs, etc. There are also cases where you can use a small tankless for situations like a bathroom that is in a church and maybe used once a week for a few hours. There a small tankless could be installed and save the standby losses that you'd have for days when it's not used at all. You can't just paint all the applications with one brush.

Observed by whom? And how does that relate to the std tests that all water heaters must undergo and show?

That about sums it up, eh?
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What a bunch of bullshit you post this, must be hallerbs phony post..
1 Ng prices out pace inflation overthe long term, the trend is and always has been up, only an idiot looks at the last year to determine a long term price trend. So what you also say is why insulate, why upgrade heating or windows, there just isnt the payback, dumb.
2. 90% of a tanks heat loss is up and out the chimney, you dont save any thing, you dont heat the basement, you loose. "Tanks are pretty efficient from a standby loss" learn about EF ratings , the majority of tanks are 55-65 EF, a 65 EF tanks wastes nearly 35% in standby loss. There is nothing efficient about that number
3 You are dreaming, or lying youself and everyone because you ignore gov specified efficiency rating tests of domestic hot water heating systems. The EF rating, that all tank and tankless systems are tested by. Go look at EF ratings on tanks with power vent, most are 65 EF. The worst tankless Ng is 82, the best go to go to 94 EF, no tank is above 83EF. www.energystar.gov has all systems rated
4 Your statements are meaningless in determining what everyone wants to know, and that is how efficient is a tank, Again you ignore EF ratings, Energy Factor, a gov required standardised test that determines the efficiency of domestic hot water systems. If you learned and studied EFratings you wouldnt post all your lies. Or maybe you would if you are a tank maker. www.energystar.gov has all tank and tankless systems rated Why dont you learn the truth about how unefficient a tank is and research EF ratings. EF is how domestic hot water systems are rated, itis the gov standard. www.energystar.gov has all tanks rated. By the way I got a 5 year payback on a Ng tankless installed about 7 years ago. You statements are mostly BS. www.energystar.gov has all tanks and tankless rated.
5 So what, a cold pipe affects a tank the same way. The water isnt heated and stored by Magic, evengy heats it.
6 My AO Smith condensing tank has more controls than does my tankless by 3 x. And you compare the bottom of the barrel 55-60 EF tanks. Bottom line, Ng tankless start at 92EF
7 Lie, get a Bosch with hydro generator.
Truth, tank EF ratings are 55-83EF with perhaps 99.8 % of units sold in the 55-65 EF range. Ng tankless start at 82EF and go to 96 EF, Yes you can save nearly 50% with tankless but a more likely amount is 15-20%, but instalation costs or a poor instalation can make it worthless. They are not for everyone.
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if a tankless has a power vent, that requires power line voltage to operate.
no power no hot watewr at all.
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Mine has no blower, it can vent up a chimney, people have been doing that a few hundred years.
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<stuff snipped>
<if a tankless has a power vent, that requires power line voltage to operate.
no power no hot watewr at all.>
One winter, when power was off for three days, we heated the bedroom with water bottles filled from the gas tank water heater w/pilot light. A little wasteful of water, but more than offset in hotel costs we didn't have to pay. Sometimes newer isn't really better and in some ways, even a little bit worse.
-- Bobby G.
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Consumer Reports did tests and the answer is no.
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On Thu, 25 Nov 2010 11:20:54 -0500, "Stormin Mormon"
Now you know why top-posting is wrong.
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On Thu, 25 Nov 2010 19:58:54 -0500, "Stormin Mormon"

Wrong, Sorry Moron. Top-posting mucks up the information flow just the same as deleting all context. Different technique, same result.
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