High efficiency, high recovery water heaters

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Doesnt a dishwasher use alot of water, well if it was not efficent why am I getting a 4 yr payback, and why am I now paying 45$ for Ng where I now have a tank, where was just paying 7-9 in summer with the tankless, you have theories, and no numbers, I have numbers I dont need unproven theorys
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Yes, I'd like to see a reference for how and why a tankless is supposed to be very inefficient in supplying water on demand to a dishwasher. That makes no sense to me. It fires up and instantly starts heating the water. All the heat goes into the water and into the dishwasher, except for the heat in the water left in the pipes at the end when the use stops. The latter happens exactly the same with a tank type unit. Nor do some of the other comments here make sense:
"1. We're concerned that it might not always give us as much hot water as we want. If washing machine and dishwasher are running, and someone is taking a shower, it could be stretched to its limit, and, if someone else turns on a hot water faucet, the shower might suddenly get cold bullets or whatever. "
You presently have a 25 gallon conventional unit and need a replacement that will fit in an 18" space, which would be more of a problem in that regard than a tankless. I don't see how anyone suddenly gets cold bullets with tankless. As more water is drawn, the outgoing temp of the water just drops following a smooth line.
"2. The supply of cold water to our house might not always be high enough pressure. We get the vague impression that our water pressure varies, possibly depending on usage by neighbors. It's probably not a problem, but it's one more minor worry. "
If you don't have sufficient pressure, then how are you going to deliver so much hot water to the washing machine, dishwasher, shower, etc that the tankless can't keep up in problem #1?
"3. We're thinking of putting in new insulated hot water pipes, running through our access-only attic, to all of our hot water faucets etc. A tank water heater would keep those pipes partly warm, so we wouldn't have to wait as long for hot water after turning a faucet on. "
Any type of hot water heater isn't going to do anything different with regard to keeping those pipes warm. Conventional hot water heaters have devices in them specifically to prevent hot water from rising out of them because it wastes energy. So they aren't going to keep those pipes warm either, unless you put in a circulating pump. I thought you wanted high efficiency? The only thing insulation will do is:
a - prevent some heat loss for the water on it's trip across the house
b - allow the water in the pipes to cool more slowly, so that if it's used again within an hour or so, it will still be warm.
Both those work exactly the same without regard to how the water gets heated
"5. If it turns out to have problems, the problems are most likely to be in our pipes or whatever, and not the fault of the manufacturer. Therefore, such problems would not be covered by the warranty. A lot of people regret getting a tankless for that very reason, and feel stuck with it, because it would cost them too much to replace it with a tank, having already spent their budget on the tankless. "
This I don't understand at all and sounds like FUD.
"6. When such problems happen, the plumber often can't figure them out, and spends too much time on them, then starting thinking of that customer as a problem customer. "
Certainly FUD. If a plumber can't figure out a tankless, you don't want that plumber around anyway.
"7. If energy prices keep going up, I want to consier other options, such as solar etc., and/or maybe get a geothermal heat pump for heating and air conditioning, and get hot water from that same system. If I spend a lot on a tankless now, that reduces my budget for that. "
If you go to geo, the difference in cost you would pay now of a tank vs tankless is going to be a tiny percentage in cost of that overall system.
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RIck-
Great post...no hype, no bashing.

I did my calcs, took a look at my usage, talked with the Bosch rep.......and passed on tankless.
IMO a tankless w/h install is very much like a screw type compressor compared with a standard piston type......usage pattern needs to be matched to capacity. If usage isn't or can't be matched to capacity then a lot of advantage is lost.
cheers Bob
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That is bs, if it was true then how do I get a 9$ gas bill, with gas dryer and stove, all my usage is quick a few gallons,, but of course you cant get proof of your bs statement, Now im at a location with NG tank and now I pay 45$ a month, My Ng tankless has gotten me a 4 year payback, Again out of the woods come people that dont use them and post unsubstantiated bs crappola, I hate these tankless threads, to many morons posting. Tank Salesman.
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{{{{That makes no sense to me. It fires up and instantly starts heating the water. All the heat goes into the water and into the dishwasher, except for the heat in the water left in the pipes at the end when the use stops. The latter happens exactly the same with a tank type unit. Nor do some of the other comments here make sense:}}}}
They make a lot of sense if you look at how a demand WH works.
Take a pot, fill it with cold water and put it on the stove. Turn the burners on high. Then dump out the warm water and refill with cold water. Repeat that scenario over and over again. That's exactly what's happening when you use a demand WH for to fill a dishwasher. It takes a fair amount of heat to bring the heater exchanger tubes up to proper temp. You basically keep reheating the pan. You never get to take full advantage of the "warm up" energy. In addition, the burners in many demand WHs are rated for a 2.5gallon/minute flow rate. But most dishwashers don't fill at the rate of 2.5 gallons/minute. If the dishwasher fills at the rate of 1 gallon per minute, all those extra btu's go right up the flu. You can do the math on this yourself. The worst part is that the dishwasher refills several times in a cleaning cycle. A shower, on the other hand, provides maximum efficiency because it's using the proper flow rate for the BTU input. The downside, of course, is that if your demand heater is rated at 2.5 gallon/minute and a second person tries to take a shower, the demand heater can't provide enough hot water. If you size the demand heater to 5 gallons/minute, then you're wasting even more fuel in low volume operations.
I wasn't saying that demand heaters aren't efficient. I was just pointing out that they're not efficient across the board. If you use them at the rated flow rate, they're far more efficient than most tank models.
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Then how do explain a TH1 which is Condensing, that has a 95% efficency and 95% EF factor on propane, because the heat exchanger is extremely efficent
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That's not true--the demand gas water heater has a modulating burner and adjusts to the flow rate.
Wayne
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Some demand heaters have a modulating gas valve......some. Not all. And certainly not the low end units.
I'll say it again. I'm not saying that demand heaters aren't efficient....they are. But there are a few issues with them regarding efficiency across the board and low flow.
Geez guys, settle down a bit and read the whole post before you flame. All I told the guy was to evaluate his usage and be aware that there are some circumstances where the demand heaters, well, I'm repeating myself.
End of discussion--at least for me.
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Before it ends, I'd like an explanation and reference for a couple of your statements:
"The higher the water pressure, the larger the BTU's required to handle the same usage. "
This makes absolutely no sense. If the tankless is heating 5 gallons of water, what possible difference in efficiency could it make if the water pressure is 30 PSI or 60PSI? I have never seen anyone claim that pressure factors in at all to sizing a tankless.
I also don't buy the analogy of comparing a tankless to constantly refilling a pan heating water on the stove. You state that you are constantly reheating the pan, as if the pan itself somehow takes and holds heat. In reality, the heat is going into the water. Some is escaping as loss around the pan, to the surroundings, but that happens regardless of whether the pan is being refilled every minute or left alone for 10 mins. In fact, MORE heat will be transferred to the pan in the case of it being refilled with cold water, as the cold water will absorb more of the heat without it being lost to the surroundings.
If you refill the pan 10 times in 10 minutes, you wind up with 10 pans of barely warm water. If you leave one pan sit for 10 minutes, you wind up with one pot of hot water. If you think some energy inefficiency is at play here, explain exactly where this lost energy is going?
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On Jul 27, 7:05�am, snipped-for-privacy@optonline.net wrote:

one issue with tankless is the delay between draw water to hot water arrives.
the tankless must detect water flow, and turn on water, .........
as a tankless owner told me, we save energy on heating water, but waste water and sewer....
now admittedly its not a killer cost but it is there.
another tankless troubling issue..........
if you have temperature control shower valves the fast changing temperature from tankless can cause valve hunting, where the shower temperature doesnt remain stable......
here we have AOSMITH vertex tank type water heaters. 96% efficent without the downsides of the tankless.
one last tankless issue.
most require power line voltage to operate. no power no hot water at all.
unlike tank type heaters that have at least a couple quick showers onboard at all times...........
so one morning the power is out:( Your choice before work:(
No shower at all or a cold one...... which do you preferr:)
tankless are fine, just like the original vW BUG was....
it will take you to the same place as a more comfy larger vehicle, but has limitations. saves energy though.
if your willing to live with the many limitations more power to you. myself I prefer the comfort of a regular tank, espically when Vertex can supply both the comfort of a tank with the efficency of a tankless.....
hey ransley, you can get one when your tankless craps out in a few more years:)
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Here we go again, Hallerb you are 1 can short of a 6 pack. I think I should just call you, yo, 5pak.
Delay might be 15 - 30 seconds
Waste, my water bill has not changed, and once pipes are hot you dont realy notice anything, but of course you never used one, but think you know
What total bs, tankless dont change alot or hunt on temp , again your lack of use is lack of knowledge
A vertex is NOT 96% efficent, its near 80 EF, the burner is 96% but not overall efficency which is what you need to learn about. And notice AO Smith wont tell you EF of a Vertex or cyclone. I have a 93% AO Smith Cyclone a 80 gal 190000 btu unit. Ive had it for 6 years and its EF is near 80. Yes its saved me alot over my old tank of near 45 EF. But dont kid yourself, Tank are 15-20% less in overall efficency to tankless. Read EF ratings, not burner ratings
My 117000 Bosch needs No AC, it used 2 D batteries for ignition. Your condensing tank, needs AC
Here again I have a AO smith 93% Cyclone, give me one valid reason my tankless should "Crap out" soon you cant.
Hey 5 pak. The Vertex is not as efficent as even a Non Condensing Tankless. Learn EF rating and quit postin crap
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The added delay from the tankless is more like 5 seconds. So there is a little extra water wasted per shower, it is true.
Cheers, Wayne
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Thermal efficiency is a red herring when it comes to tank type water heaters. They are just saying that 96% of the possible heat from the gas burned makes its way into the water. There are still standby losses from storing the hot water, so the overall energy factor is likely 0.80-0.85. That's still quite good, comparable to a tankless.
Cheers, Wayne
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On Sun, 27 Jul 2008 09:54:19 -0700 (PDT), " snipped-for-privacy@aol.com"

Will 20 years or more years be close enough?
...."Most tankless water heaters have a life expectancy of more than 20 years. They also have easily replaceable parts that extend their life by many more years. In contrast, storage water heaters last 1015 years. Periodic water heater maintenance can significantly extend your water heater's life and minimize loss of efficiency. Read your owner's manual for specific maintenance recommendations."

http://www.eere.energy.gov/consumer/your_home/water_heating/index.cfm/mytopic820
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And no the vertex is near 80% in

I said a standard tank is a simple appliance that rarely requires any service, I am 51 and in my entire life perhaps one needed a thermocouple.
heres a paste from AO SMITH
Vertex offers up to 96% thermal efficiency with performance that rivals much larger water heaters
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And again, thermal efficiency isn't overall efficiency, due to standby losses. Thermal efficiency just measures how good it is at burning gas.
Wayne
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You are pushing Vertex, a complex condensing unit, more complex than tankless of higher EF, Vertex is near 80 or less EF. 96% rating is for suckers that dont know what EF is. EF is akin to AFUE.
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The low end 460$ Bosch does, any quality tankless has modulating valve. Maybe 10 years ago it was different.
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