1 - First you said the essential difference was the standby losses.
2 - Then you said how much you save depends on your usage patterns.
3 - And then you said losses from tank heaters are almost constant regardless of how much you use.
For the record, I agree with 1 and 3.
For me, I look at my gas bill in summer, when all gas is used for is the water heater and my outdoor gas grill. It's about $17 or so a month and that is with a std efficiency water heater. That includes those standby losses and usage. I could surely do better with a high efficiency tank type. From that, I've concluded if I need a new one, I'd go with a tank type higher efficiency one.
One simple test to settle the standby loss issue would be to read the gas meter before going away for a few days to a week. Before doing that, draw enough water to fire it up. Upon returning, see how much gas it used.
The heat goes up the chimney on the uninsulated center, Tank EF ratings are 55-83. tankless are 82-96, 15-35% are standby losses. Again you continously post wrong info.
1) Natural gas prices have been very low the past few years, and there's no indication that's going to change in the next few years. Anything you spend to reduce natural gas usage will have a proportionately small return on investment given low gas prices.
2) Conventional hot-water tanks are pretty efficient from a standing-loss standpoint, and what little heat they do radiate can be reduced by a relatively cheap external insulation blanket. On the other hand, the radiant heat loss from the tank is captured inside your house, the advantage of which is proportional to your northern geographic location (or as a function of altitude).
3) heat loss from a conventional tank flue is minimal if you have a power-vented system (when the fan isin't turning, it's acting like a baffle preventing air flow through the flue). I suppose a power-operated shutter could be added to completely close the flue and prevent heat loss when the burner is not on.
4) efficiency of heat transfer is inversely proportional to the heat gradient. The burner of an on-demand heater needs to put out 10's of thousands, even 100+ thousand BTU in order to heat incoming water during the water's short residency time inside the heater for the water to reach conventional hot-water temperature (typically 140 to 160 f). The more north you are, the colder your incoming water supply will be, and the more capacity (in BTU) the burners will need to be to bring the water up to the desired temperature. Exhaust heat loss from these units is significant while they are operating, and during their off-cycle as they cool down they can't dump much heat energy into the water because there isin't much water stored in the unit.
Conversely, the burner of a conventional water tank is capable of much less BTU heating, and the heat from the burner has more time to come into contact with the internal tank surface and transfer it's heat into the water. The exhaust gas temperature in the flue of a conventional heater can be so cool as to require a small electric blower to properly exhaust the gas out the flue. This is an indication that most of the combustion heat is being transfered into the water and not being exhausted out the chimney.
In other words, perhaps 50% of the combustion heat of an on-demand heater is actually being transfered to the incoming cold water and the other 50% is being lost in the exhaust, while 80% of the combustion heat is absorbed by the water in a conventional tank. The difference is that an on-demand heater is on perhaps 30 to 90 minutes per day, while a conventional tank might be on for 4 hours a day. But remember that when a conventional tank is on, it's burners are using a much smaller amount of gas compared to the on-demand heater.
5) the efficient use of an on-demand heater is challenged by short hot-water usage events. In most houses, the hot water lines are minimally insulated and thus the water in them quickly drops to room temperature. Anyone turning on a hot-water tap in an upstairs bathroom will notice it take 10 to 30 seconds to actually get hot water. It doesn't matter what type of heater you have (assuming the heater is in the basement). A short hot-water use event (say, washing your hands) will end up dumping a lot of waste heat out the exhaust when an on-demand heater is signalled to turn on and then soon after turned off to heat the water for that short-use event.
6) because of the very high heating capability (BTU capacity) of on-demand heaters, the extreme thermal cycling of their internal components will age the unit much faster than a conventional water heater, and they do or will require more maintainence and repair vs a conventional water heater (they have control devices, electronics, etc, that are not present in conventional heaters, and as we all know - electronics and HVAC equipment really don't tend to co-exist very well for the long term).
7) on-demand heaters have electrical or electronic controls that require a source of AC current. Thus they will not function during a power failure. Anyone living in a northern climate that is subject to sporadic winter power failures will not appreciate the lack of hot water during extended outages.
Conclusion:
No home owner that has a working conventional gas water heater will ever live long enough to recoup the savings from replacing his existing working heater with an on-demand unit - and it's not a given that there will actually be any measureable savings in gas use.
What has been observed is that the behavior of occupants change in terms of how they use hot water when a conventional heater is replaced with an on-demand heater, and that change usually results in less hot water use (shorter showers, changes in shower heads, installation of low-flush toilets, etc, insulating hot-water supply lines inside the house) so it's not always clear where the savings come from and why.
Replacing an old / leaking conventional water heater is very easy for most novice home owners / handymen, and at a cost of only a few hundred dollars, the cost/reward ratio is still heavily in favor of replacing a old conventional water heater with a new conventional unit.
You will get more bang-for-the-buck by
1) putting an insulating blanket around your existing or new conventional water heater
2) insulating as much of the hot water supply lines inside your house as you can reach
3) use a low-flow shower head
On-demand water heaters are basically a crock of shit designed to give plumbing and HVAC companies a very lucrative new revenue stream.
You need to go back to school, what you state is nuts. No gas boiler is over 100% efficient, no gas boiler is 100% efficient, the best is around 98%. There is wasted heat out the chimney and there is the loss. If you burn an unvented flame inside like a gas stove, that is
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?
I asked my gas company what my bill would be if I used no gas at all; their answer: about $17.00. That amount helps pay for physically reading the meter, mailing out a bill, recording the payment, etc. I can't begrudge them the admistrative fee.
So, living in a converted duplex, I connected the gas lines from the two sides of the building and cancelled the service to one side.
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.
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.
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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.
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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.
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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.
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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.
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.
There you are wrong, a Btu is a Btu and this is 6th grade stuff, you cant get back more btus then you put in. Its a fundamental part of energy. If you could get more out than you put in your reasoning would lead to perpetual motion of other energy forms. Look at our AFUE ratings for furnaces, we correctly rate that condensing furnaces and boilers start at about 92% and go to 98%, its tested and proven by science you dont get more than you put in burning gas for condensing units. You still waste energy with condensing units, it goes out the chimney. I have a condensing furnace, boiler and condensing AO Smith water tank, None of mine are rated over 96% and nothing sold is rated over 100%, even 99% is likely a lie as heat is wasted out the chimney . If your point was correct running a stove would be over 100% efficient, but it takes energy to condense water.
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