Tankless water heaters

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These are very common in Europe. I lived over there for years and always had hot water instantly. Of course, the manunfacturers available here likely different from Europe. It's best to talk with someone in the area who already owns the one you are considering.
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Tankless water heaters were a standard "low end" product when I lived in Asia (~15 years). The better apartments had hot water tanks.
My experience with gas-powered tankless heaters is that they are, indeed, a low-end product, where the primary advantage was that they didn't take up any floorspace. (The average apartment in Asia was about 600 sq ft total, so every inch of space was used.)
People on this thread are asking the right questions, especially about flow rate. In my experience it was difficult to balance temperature and flow rate; when you decreased the flow of hot water to get a comfortable temperature, you could reach a point at which the gas suddenly cut off and you went to full cold. Given the low cost and reliability of conventional hot water tanks, I don't think the pay back period of a tankless heater is persuasive.
I suspect installing a tankless water heater is a little bit like buying a diesel car, being responsible for the two happiest days of your life -- the day you first start to use it, and the day you finally get rid of the #%$&^%# thing.
When we remodelled, I chose instead to put an additional hot water tank adjacent to the new bathroom, which gives me almost instant hot water. Regards --
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Temperature and flow rate is now computer controled with a full modulating gas valve so temp stays the same when it is on from start to full flow. Older units lacked this. at very low flow it will turn off, that is a drawback but it doesnt bother me as all my faucets are low flow so I ususly just turn them on full. My payback will be 4-5 yrs switching out an electric tank. I have no complaints after 2.5 yrs.
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Yes - the new tankless units are nothing like the low end stuff we saw in the past in Europe. Today - the new units are computer controlled - and are relatively bulletproof. Some are 92% efficient. They have digital wall gauges that allow you to tune in the temp you want within one degree.
I am planning to replace two 50 gallon electric water heaters with one unit - Rennai - Bosch - Akagi.
My city give a $450 rebate for converting and electric water heater to gas - so I may put two in the house - that way I have one as a back up :-)
Harry
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Tankless heaters now have computerized controls that eliminate the wide temperature fluctuations you experience with the older models. I was also in Asia during that time frame and remember how quickly I woke up after taking a shower where the water temp swung 40 degrees.

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My neighbor has a big house. He had two gas tank water heaters. He replaced them with two "takagi" tankless water heaters - had them installed for $500 each. Now this guy is a wealthy fellow and money does not matter to him - service does. The tankless water heaters produce endless instant hot water - no lag - no nothing - turn the faucet on - hot water comes out now. He can have four showers running at once and the hot water still does not run out.
The units are very small - less than 2 x 2 x 1. they do not require electricity - so you have hot water even in a power failure. They have a battery igniter.
A restaurant down the street has one. They do piles of dishes daily. They depend on that "rennai" tankless water heater. It does a great job. their business would go down without it. they have been using it two years without one down time.
Also - since we leave our home a lot - we will not be heating a tank of water and wasting energy keeping it warm. When you are away - everything is off. It only turns on when you turn on the hot water faucet. I am going to install my tankless heater on the outside wall just 4 inches from my showers.
Also my city will give me $450 for every electric water heater I replace with a gas one - so this is an easy decision.
The new technology in tankless water heater is fantastic. Yes - conventional water heaters are cheaper than tankless - but but tankless are cheaper to run and much more efficient.
I am going to install one or two.
Harry
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Harry Everhart writes:

This defies elementary thermodynamics. A smaller heat exchanger with less time of contact cannot possibly be more efficent.
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I am not that smart either. Here are some charts from the Department of Energy -
http://adwords.tanklesswater.com/ed_costsavings.asp
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Harry Everhart writes:

That's a boob-bait Web site with stupid claims, not a government source (not that Jimmy Carter's DOE would necessarily be sensible).
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Not only no standby loss but no pilot loss and no thermal loss on pipe to tank. My small Bosch is 2 D cell battery ignition, no pilot. Effecienceis of tankless are 81 - 94%, 94% for the new Takaki. Tanks calcify on the bottom with scale. I recently removed a tank in my apt building on relativly soft water. There was 14" of scale in the tank, now that kills efficiency. Tankless dont loose efficiency as tanks do. There are many sites showing individual units efficiencies. Overall going from electric tank to Ng tankless my bills are down 75%.
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I have the impression that lots of tankless heaters keep a small part of themselves warm all the time.

That wouldn't change the efficiency of an electric heater.

They never scale?
Nick
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In raising X amount of water Y degrees. Yes.
But that's not all there is. What about all the energy you waste when extra hot water you've had to run for 60 seconds to get _any_ warm water to the tap, sits in the pipes overnight? With tankless, that's not an issue.
Efficiency, to mean anything, has to include the whole system. Including heat loss off the pipes.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
  Click to see the full signature.
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Chris Lewis writes:

That's a point-of-use issue. Nothing to do with tankless.
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Dear Rich - No matter what we say - you are not going to be impressed. That fellow told you he saves 75% on his tankless gas water heater - but your mind is made up. We don't want to argue with you - if you don't agree - don't buy one. But we have studied this to the point of purchasing them. My neighbor put two in just a few months ago - and loves them. You seem to just want to argue. I do not like evangelists that try to convince folks to do something pro or con - especially when they have nothing but a cranky opinion - but no data to back it up. On top of all that - my city likes them so much - they are willing to give me $900 in rebates just to install them. As much as I value your opinion - please present information showing that tankless heaters aren't as good as tank types. I am willing to listen to other information - my mind is not closed - but it must be more than someone just arguing for argument's sake. Thanks for caring about us so much to try to convince us not to make a mistake. Harry
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If you get one with a standing pilot sure there is the pilot loss. That is the Bosch 80-81 % units . From pilotless efficiency goes from 82% up to 94% depending on unit and manufacturer. Harry E., Rich Kinch has been all over trying to put them down and calling companies like Bosch fly by night. Bosch should anyone care to look at a company report is like our GE or GM , big and established. Kinch probably can`t afford one so this is his justification and cuts them down baselisly
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Harry Everhart writes:

As regards efficiency, I did: simple thermodynamics, time, and space. Heat exchangers become *less* efficent as they get smaller and faster, not more.

I am not an "evangelist". I am a skeptical engineer, with reasons to be skeptical. The burden of proof is on you if you claim the old ways are obsolete.
Look at the hucksters and swindlers that sell these things.
Look at the testimonials instead of metered testing.
Look at the performance claims that defy elementary BTU calculations.
Look at the absurd claims about how bad conventional units are.

Wrong. I am impressed by facts and analysis. Not testimonials that defy freshman physics.

This is exactly the response of those who won't accept the truth when the truth doesn't fit their candyland ideas. This is the response of advocates of perpetual motion machines, 100 mpg automobiles, 50000X Rife microscopes, lifetime paint, magnetic water softeners, septic digesters, $1200 boom boxes, bagless vacuum cleaners, waterless cookers, light bulbs that don't burn out, plates that don't break, stuff to pour in your gas tank to fix your engine, knives that never need sharpening, glue that sticks to everything, and the fountain of youth.
Show me some engineering analysis and testing. Guys with meters and thermometers who aren't trying to sell something. Not sales brochures, not testimonials, not reports from across the ocean in another alphabet and language. Loan *me* and unit and let me run it through my laboratory.
Show me somebody in the USA who makes these things that I can sue when their claims of 75 percent savings is proven to be the bunk that it is.
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Kinch the Grinch you are a true moron
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Hey Kinch the Grinch you Stupid Shit, did you know you can get a 96.7% efficient furnace. Did you know you can get a 97% efficient WH tank, go back in your cave kinchy.
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I was told by a plumber that if I wanted one of those, I would also have to replace my 1/2 inch gas line with a 3/4 inch line which would add considerable cost to an upgrade. check on the requirements of the heater you want and the size of your supply line to know if this will be an issue.

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I am also interested in these tankless heaters... What concerns me is the minimum flow rate to trigger the heating action... Would a faucet that was not on full blast (ie a trickle for washing dishes) be enough flow to trigger the heater?
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