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Old 01-04-2011, 12:25 AM   #31 (permalink)
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Originally Posted by t vago View Post
Have you thought about using one of them demand (or instant) water heaters? I first encountered them when I rented a house in Japan, then another one when I rented an apartment in Italy. They're wonderful because they give heat almost instantly, they never go cool on you, and you're not having to continually heat up 30 or so gallons of water that you may not be using at the moment.
They are used mostly in situations where hot water is not needed every day, or where space saving is above all else as the energy savings from the on demand hot water heaters tends to take the 20 year life of the water heater, add to that the acid flush to keep it functioning properly and it's a net loss.

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Old 01-04-2011, 07:13 PM   #32 (permalink)
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Originally Posted by t vago View Post
Have you thought about using one of them demand (or instant) water heaters? I first encountered them when I rented a house in Japan, then another one when I rented an apartment in Italy. They're wonderful because they give heat almost instantly, they never go cool on you, and you're not having to continually heat up 30 or so gallons of water that you may not be using at the moment.
But they are usually but not always electric which can be a cost issue in some areas.

I have been searching for the so called "Worlds Most Efficient Water Heater" I saw last year for a while, blast why don't I bookmark everything.

Anyway it only lost 1deg per week and it could be heated with any source you wanted be it solar, electric or gas.

Anyone remember that one?
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Old 01-04-2011, 08:50 PM   #33 (permalink)
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Nope, don't remember anything about any "World's Most Efficient Water Heater."

I do know that you can find natural gas models of instant water heaters, that you are able to use them every day, and that you could mitigate the need for an acid wash with using softened water. Pricewise, they're now comparable in price with more traditional water heaters.

Natural gas versions of these things are used almost exclusively in Europe and Japan. Over there, they think it's supremely wasteful that we Americans always heat about 120 or more liters of water that we don't immediately use. Their hot water tanks, which are hard to find, tend to be placed on either a wall switch or a timer (Hm... that's an idea...)

It's a cultural issue as much as anything, I suppose.
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Old 01-04-2011, 10:01 PM   #34 (permalink)
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Originally Posted by t vago View Post
Nope, don't remember anything about any "World's Most Efficient Water Heater."

I do know that you can find natural gas models of instant water heaters, that you are able to use them every day, and that you could mitigate the need for an acid wash with using softened water. Pricewise, they're now comparable in price with more traditional water heaters.
The thing is they may not actually have a lower cost of operation as compared to a traditional model or especially a very high efficiency insulated model like the solar guys use. If I use 20 gallons a week of hot water and have a very well insulated unit, it is likely the amount of energy lost is the same but the efficiency of the element heating the water may not be as efficient on an instant heater versus a slower unit. I was always taught with heat you can be slow and efficient or fast and inefficient but most likely not both at the same time.

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Originally Posted by t vago View Post
Natural gas versions of these things are used almost exclusively in Europe and Japan. Over there, they think it's supremely wasteful that we Americans always heat about 120 or more liters of water that we don't immediately use. Their hot water tanks, which are hard to find, tend to be placed on either a wall switch or a timer (Hm... that's an idea...)

It's a cultural issue as much as anything, I suppose.
I'm not sure its a cultural thing, americans have a lot of space for crap like water heaters but our companies are VERY VERY glacially slow at changing anything. If I can go to home depot and lay down $250 and get one its more likely I will have one than if I have to order it or if its not displayed. Same thing is true when a contractor doesn't support or recommend something.

Once market penetration occurs and larger names are offering them in decent price points at the local building dumps you will see them in many homes.

I like the idea of instant heat and have always believed it should be used as an AUXILLERARY source.

AKA high efficiency gas primary and electric water heater BOOSTER near the faucit.
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Old 01-04-2011, 11:16 PM   #35 (permalink)
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My gas water heater sits in the basement. I am thankful for whatever heat it "loses" there.
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Old 01-05-2011, 02:28 AM   #36 (permalink)
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Quote:
Originally Posted by rmay635703 View Post
I have been searching for the so called "Worlds Most Efficient Water Heater" I saw last year for a while, blast why don't I bookmark everything.

Anyway it only lost 1deg per week and it could be heated with any source you wanted be it solar, electric or gas.

Anyone remember that one?
Here is something similar: heat accumulator. It's an oversized water tank that can be warmed with any kind of (waste) heat that is available or cheapest at the moment, and is superinsulated to keep as much of that heat as possible from being lost (5cm of foil-backed mineral wool plus 30-40cm styrofoam). If sized right it can take care of a home's heating needs (water and space heating) for a few days.

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Natural gas versions of these things are used almost exclusively in Europe and Japan.
I have one! I have one! Or two, actually, one for each floor. On demand heaters were very common here, especially in apartments. I've seen water tanks in apartments in the US, but not here. Just not enough space when a 6-person family is living in a 45m2 flat. Recently electric units are becoming more popular in apartments since they are smaller and don't need fresh air and exhaust ductwork. In new houses water tanks are more popular than they were years ago, but nowhere as popular as in the US.
The setup we have, which is not new or hi-tech, is quite inefficient, since it takes a while for the hot water to get to the faucet, plus there is a minimum flow below which it shuts off.
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Old 01-05-2011, 02:32 AM   #37 (permalink)
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I have one too. Home loan dropped a couple points because we had one installed. Depends on where it is installed how and how long the hot water pipes are from origin to destination.
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Old 01-05-2011, 11:50 AM   #38 (permalink)
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Since my gas hot water heater is 12 years old I have been looking around in advance of its demise.

AO SMITH makes two very efficient tanked water heaters. The Vertex series. One is 90% eff & one is 96% eff. The 96% heater costs an arm & a leg at MSRP $1999 USD. Which pretty much ruled it out for me. Not sure about the 90% price.

They run a coiled chimney up through the tank to extract more heat from the exhaust. The 96% has to be power vented. They have extra valves for thermosiphon or radiant hot water heat as well. At least one needs a drain for condensate. I assume they are heavily insulated, but more doesn't hurt.

Can an instant heater be used inline with a tank heater? Will the instant stop heating once the tanked hot water gets to there?

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Old 01-05-2011, 01:40 PM   #39 (permalink)
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Heatpump water heaters are very efficient:

Preview - Heat-Pump Water Heaters - Fine Homebuilding Article
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Old 01-05-2011, 09:06 PM   #40 (permalink)
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Can an instant heater be used inline with a tank heater? Will the instant stop heating once the tanked hot water gets to there?


Like the other guy, I wish I bookmarked more stuff.

I've seen setups where the instant heater maintains a super-insulated large tank, and starts up before the tank gets very low so as to keep hot water flow constant. For a household of commuters (students & workers) where use is at peak hours with high consumption of hot water it made sense to me to investigate.

One can add in all the other types of hot water generation as desired (solar, A/C heat exchanger, etc) to further offset costs.

One does not need 3, 4, 5, 6, small instant heaters but modifies the present plumbing system to best effect.

Granted each situation deserves careful examination, as a hot water system that has nothing to do with heating the house itself can be problematic as to cost, complexity and reliability in a hurry.

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