Tankless water heaters

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Steve B wrote:

35 years(a rental unit),capacity enough to fill the bath in reasonable time. No problems, and regular yearly maintenance from the rental company. At work we had the a small electrical unit in the garage for washing your hands, very handy, luke-warm water within seconds.
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Sjouke Burry wrote:

Oh, the rental of the gas unit is 136 Euro per year, maintenance or replacement included. And the price of energy for gas is much lower here then the cost of electricity, so it is also used for heating.
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On 11/10/2010 12:06 AM, Sjouke Burry wrote:

Bosch manufactures an interesting NG tankless heater that has a small generator powered by the flow of water through the unit that supplies electricity to the control system and electronic ignighter. With no standing pilot light, it's one of the more economical NG instant water heaters I've seen.
TDD
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Answering all your questions is a big job but here are some quick points, I have a 119000 Ng Bosch got it for 500 and its good for 1 shower and I never need it on high even with 40f incoming water. Instalations fail when you dont do your homework on your gas supply and incomming winter water temps and use. They use alot of gas and need all of it in winter to give you rated output, in winter on the coldest days gas can have reduced flow from the supply and has to be figured in. For 2 showers you need to go up to a 190000 btu unit, kids will ruin any saving knowing HW is endless. Savings go down percentage wise the more people you have and it may not payback with a family of 4-5. A single person will save the most, I got a 4-5 year payback but did my own install. You need to do alot of research and testing before buying one, it may or may not be a good idea for your situation. Is getting the needed gas supply means new piping, and instal is difficult, the cost of a 190000 btu unit can be thousands.
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Prof Wonmug wrote:

I just got a tour of my friend's new system. It's about the size of a bathroom medicine cabinet. Has three 240V 40Amp heaters. 120A is no big deal for him cause he just put in 400A service. For most people, that would be a problem. Also, there's the major expense of the electrical work if you have to pay to have it done.
Gas would have it's own set of issues.
Once you've picked an energy type, you pay the same to heat water no matter what technology you use. A BTU is a BTU. The only difference is the losses in the system. If you use a lot of hot water, I can't imagine it saving much of anything. If you use no water, the energy saved by not radiating from your hot water tank and the pipes between the source and the point of use might be a significant percentage...but still maybe not a big absolute number of $$.
Might be a different situation if your house was optimized at design time to with all the points of use a short distance from the tankless.
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On 11/10/2010 4:39 AM, mike wrote:

Me and my friend installed an electric two module instant water heater for his sister. It's installed in the utility closet with the washing machine and electrical panel so we didn't have to run a lot of wire. The only problem with it is adjusting the rate of flow. For that, we installed ball valves to adjust how fast water goes through the heater. A gallon bucket and a stopwatch is what we used to determine rate of flow so the heater will work. What most folks don't understand about tankless water heaters is the fact that you're not going to get the full flow of the rest of your water supply unless you install a very high capacity heater. The water has to spend enough time in the heat exchanger to absorb the heat. If I installed a tankless heater for myself, I would add a tempering tank to help bring up the temp of the incoming water.
TDD
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Yes, yes, yes. Distance from the tank is critical, and can be designed in the construction phase. We are currently remodeling our kitchen. The builder had the hot water heater across the house, and we literally didn't have hot water in the kitchen for three years. Then we put in a 110v. 8 gallon hot water heater just the other day, and glorious hot water. I am going to put a small one in my shed for beer brewing. Point of use and distance from source is critical in any system.
Steve
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Check out systems by a rating system that is standardised, E.F. Energy Factor and you will find a Btus are not Btus that are all equal from the standby loss. Tanks are mainly 55-65EF, tankless Ng start at 82 and go to 94
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Re Tankless water heaters:

No. Compared to a well insulated conventional water heater, the pay-back for the tankless is longer than it's service life.
There may be other reasons that make it worth while, but cost saving isn't one of them.
--
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wrote

They are VERY worth while if you are selling them. ;-)
They ARE actually cost effective in some situations. We do HOA analysis. I have seen several in clubhouse and pool house bathrooms under the sink, and in those situations where no one uses the water for sometimes hours and days at a time, and warm water is all that is needed, it is better than the currently high priced water heater and keeping water hot and ready for five minutes of use a day. And I mean SMALL ones.
Steve
Steve
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The I guess im dreaming when I run my numbers of my 4-5 yr paybck with my Bosch tankless, I guess my bills are phony and a mistake.
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Can you post some numbers so we can see what you're talking about? The problem I have with tankless is I look at my gas bills during the summer months when the gas is just used for the water heater and my gas outdoor grill. Those bills are under $20 a month, usually in the mid teens, which includes both usage and standby losses. I live in NJ where NG prices are probably among the higher ones. So, I'm having a hard time figuring out how standby losses can amount to more than $5 or so a month. In that case, in 10 years, they only amount to about $600. Which is less than the difference in cost between my conventional, not high EF, water heater and a tankless install.
I'm not saying they can't be a good solution for some applications. Just that I have doubts that you can get a payback in 4-5 years.
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snipped-for-privacy@optonline.net wrote:

I replaced a fairly new tank with a Bosch tankless in 2004. The house has two water heaters. One (still a tank) feeds the bedroom end of the house with it's bathrooms. The other, now a tankless, feeds the kitchen and laundry. When we put in the tankless, our summer gas bill dropped from $20 to $10 in the months after the switch.. There wasn't any change in the number of people in the house or how we used gas or the gas rate.
I figure the tankless cost $500 more than a tank, so that would be a 4 year payback. You would be right not to put a lot of faith in those gas usage numbers, I don't have any way to track it in detail. -- Doug
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On 11/11/2010 5:47 AM snipped-for-privacy@optonline.net spake thus:

Hmm; interesting that in your replies to me above you were fairly pro-tankless in terms of energy savings, while you're much more cautious here.
I think what this really shows is that any energy savings due to tankless water heaters is pretty much on the margins. This isn't a bad thing from an energy-saving standpoint, of course: a therm saved is a therm saved (or a kilowatt). But it does indicate that calculating any kind of payback period for installing tankless heaters is problematic at best. This is where I think that some kind of curve showing usage patterns vs. fuel savings might be useful. I can accept the assertion that tankless heaters save energy overall; it's just not that apparent how much, exactly, they save or whether installing one is a good decision financially speaking.
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It's not that complicated. Tankless water heaters save in (maybe) two ways. The first way is standby losses. Tankless have none. Tanks' standby losses depend on how well insulated they are, but are constant with time, independent of usage. The savings I quoted in a previous message are almost all standby loss savings, we don't use a lot of hot water at that end of the house.
The second possible savings are any efficiency differences in actually heating water. I think most tankless are better than most tanks, but I haven't studied it recently. -- Doug
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On 11/11/2010 5:56 PM Douglas Johnson spake thus:

So it might be a toss-up between tankless heaters and those newfangled high-efficiency tank heaters that were mentioned in this thread ...
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On Thu, 11 Nov 2010 19:56:31 -0600, Douglas Johnson

I've seen about 16 or so tankless installed over recent years. Plan ahead...( in the desert here)
Zoned: Master plus hall powder room get one (outside) install. The far wing on the house ( 3 BR, 3 Bath) segregates the curtain climbing children or guest so they get one outside installed unit.
The mutual location is the kitchen. One unit installed inside the garage covers the kitchen, laundry and garage.
No zones? Install the units in tandem. 1,2,3 side by side, work in tandem and fire the heat when demands call for the second heater. The third tandem -- extra heat.
Tandem installs are perfect in the garage, on the wall with each access for viewing and inspection. Also mount power exhaust vents through the block wall.
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I'm not pro-tankless or against them. My earlier posts were comments on your analysis that somehow because a tankless, which has a larger burner, uses a lot of gas during the periods it's actually heating water, that it becomes inefficient compared to a tank type if you use it frequently. Whther you use a small burner for a long time or a large one for a small amount of time, the only thing that counts is how much hot water you get out for a given gas input. I've seen nothing to suggest that tankless are inefficient if used frequently. Quite the contrary, that is an application that they are efficient at and also suited too, because the water supply is endless.
It seems just about everyone here agrees that the main energy savings of a tankless versus a high efficiency tank heater are in the standby losses. Whether you can save enough on energy to make the tankless install pay back in a reasonable period depends on the particulars of the actual situation. And also, other factors, like having unlimited hot water or not having to keep a tank hot for an application where hot water is needed only every 3 days, etc, can also play a role.

If you agree that the main difference is that the standby losses are eliminated, then you don't need a curve because it doesn't depend on the usage. It's roughly the standby loss, which is constant.
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On Nov 11, 7:47am, snipped-for-privacy@optonline.net wrote:

Actualy its less than 4 years, mine is the small 500$ unit with an extra 100$ exhaust blower, I put it in myself. It is a bit difficult to go over but in reality I saved 25$ a month because I went from electric tank to Ng, but electric costs have to be converted as they were about 30% higher per btu then. The electric tank was a 5 years old, well insulated with foam and a blanket so I consider it a good effecient unit. My gas went up in summer about 4-5$ a month to about 15$, my electric down 30 a month without ac running, a savings of 25 a month or 300 a year. But considering electric was maybe 30-40% higher per btu a 15$ a month comparison is better to Ng and that is a 180 a year or 720 over 4 years and I give myself something for the install. But I cut usage, insulated pipes so I think 4 years is a fair guess. But if you pay 1100 for a unit and 500 for an instal its a different game. So you see it isnt easy running the payback numbers and doing it right, but its saving me alot. Look at it this way, the only difference in EF rating from tank to tankless is standby loss. EF testing is standardised. Tankless go 93-96 EF is condensing and 83-86 non condensing. Tank start at 55-60 EF and go to about 82-83 EF. The only difference is standby loss which is about 15 %. So 15%
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http://www.rinnai.us/tankless-water-heater/faq/#question-6
See question 9
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