HOT WATER ON DEMAND, HEATERS

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Maybe you've spoke of this subject B-4.
But I see Lowes big box store has a variety of instant hot water heaters. The one like Rinnai <sp>...
Are these water heaters worth the price to switch out from a water tank?
There are various models and prices... Have you had any experience with any at all? Are they efficient? Is Rinnai the only one to trust?
Seems to me that a great deal of money can be saved using these heat on demand units...am I wrong?
Please comment on what you know.
And I thank you for any input...
Pat in Denver
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Papa Pat wrote:

Fine for instant warm(not hot) water to wash your hands. So it depends on the type and usage .
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Make up your mind Harry.
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.

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On Nov 20, 12:30 pm, snipped-for-privacy@optonline.net wrote:

or tturn existing tank to vacation, come back a day or two later.
how warm is the water?
standby losses are overstated, in a heated basement standby loss helps to keep your home warm in winter..
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That's worth repeating for the logically impaired.

Joe
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Oh give him a break, he has to make up a reason to justify his tank is best.
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That's good to know. I don't have a basement but I do have an attic and that's where my water heater is. ;-)
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...and have done *nothing* since. Well, there is that RR engine on the A-380. That's a nice piece of work. Oops!
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wrote:

They were leaders in jet aircraft. Remember the DeHavilland Comet?
http://en.wikipedia.org/wiki/De_Havilland_Comet
It was involved in the first fatal crash of a passenger jet airliner. Soon afterward one dropped into the Indian Ocean . . ."The crash was attributed to structural failure of the airframe with witnesses observing the wingless Comet on fire plunging into the Indian Ocean."
On 10 January 1954, 20 minutes after taking off from Ciampino, Comet G-ALYP ("Yoke Peter"), BOAC Flight 781, broke up in flight and crashed into the Mediterranean off the Italian island of Elba, with the loss of all 35 on board.'
And who could forget the White Star Line's most famous ship, the Titanic?
-- Bobby G.
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On 11/23/2010 4:19 AM, Robert Green wrote:

I thought the Titanic was built in Ireland? Oops, Northern Ireland, does that count? :-)
TDD
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Silly boy. The English owners wouldn't want to pay British steelworker or real estate rates. They exploited the Irish in the finest tradition of an Empire:
http://en.wikipedia.org/wiki/White_Star_Line
"The first company bearing the name White Star Line was founded in Liverpool, England by John Pilkington and Henry Wilson, and focused on the U.K. - Australia trade, which had increased following the discovery of gold there . . . the company's bank, the Royal Bank of Liverpool, failed in October 1867. White Star was left with an outstanding debt of £527,000, and was forced into bankruptcy. On 18 January 1868, Thomas Ismay, a director of the National Line, purchased the house flag, trade name, and goodwill of the bankrupt company for £1,000, with the intention of operating large ships on the North Atlantic service. Ismay established the company's headquarters at Albion House, Liverpool."
-- Bobby G.
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On Tue, 23 Nov 2010 05:19:02 -0500, "Robert Green"

"How many more must die!"

harry's favorite.
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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.
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<snip>

Explain how that is helpful in Central TX?
<g>
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snipped-for-privacy@optonline.net wrote:

That $17 probably includes overhead.
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.
Saved $17 bucks a month.
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Papa Pat wrote:

Facts:
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.
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Home Guy Said::::

Well, nobody ever `splained it to me that way before.
Thank you... I read your whole soliloquy, and I do understand what you wrote.
Especially that changing over to an on-demand water heater will never return what you spent to install it...EVER.
You may get an argument from some in this group... but I thank you for making me understand the big picture...
And thanks to all who took the time to respond as well....
Pat in Denver
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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 100%
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It sure isn't the first time, either. They must have lost their way in science in the UK since the days of Lord Kelvin and Sir Isaac Newton.

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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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