I noticed some whole house 4 bath electric tankless require 300A service...so your 200A would not be enough for those (3x60A). I have decided that the ones that work on 2x50 and 2x60 circuits would not be all that great due to my cold ground water (very cold deep well water).
I am however considering a couple of 30A tankless as boosters for a couple of my showers (or one 40 or 50 amp one since they are close and on same line). Its a long run and takes longer to get really hot water from other end of house than to take a shower, so its either take a lukewarm or cool bath or wait. What do you guys think of them for that application (that is localized boost heating)?
In reality I am not at the edge of my hot water capacity. You are accurate in that my gas water heater is rated at 2.09 gallons per minute @ a 90 degree temperature rise. That is pretty much identical to your calculation.
This morning I measured the water consumption while I was taking a shower. With everything set for a normal shower, I used about 1 gallon per minute of water during the shower. About 1/3 of that water was cold water (40 degree temperature).
So, the way that I see it I have plenty of water heating capacity to spare. The use of about 2/3 of a gallon per minute of hot water during a typical shower does not strain the heater at all.
That CU article was more than just annoyingly bad- it's downright disinformational!
In reality, if you use less than 60 gallons of water/day, your tank HW heater will perform LOWER than it did in an EF test (and far lower than the high-volume test the CU folks performed.)
Similarly, if the bulk of your water is a gallon or less at a time (say, primarily for hand-washing, and you only wash clothes or take baths once/week), your on-demand won't meet it's EF numbers, may even perform lower than a decent tank (but not likely.)
There's a ton of information (prolly more than you ever wanted to know :-) ) on the subject here:
For the true tankless performance, take a look at Fig 5.1 (p. 48 of the .pdf, or 42 of the printed document). At 2 gallons/draw it's no better than a tank's EF performance, but it'll clean the tank's clock at anything over 5 gallons/draw.
Here is more succinct & graphical comparative test summary from PG & E than the WHPAGette_Final.pdf document that demonstrates just how much of a difference actual use patterns effect operating efficiency (and how truly sucky standard-efficiency tanks perform relative to their EF numbers at low & moderate levels of more realistic use than an EF test):
Even one of the CONDENSING tank systems (heater #4) couldn't muster 70% under moderate use(!), and in the mid 60s under low use. The only tankless that was tested was a condensing version (heater #6- they didn't specify whose that was), and it too suffered slightly under low use, but not nearly as severely as standard efficiency tanks or even the crummier condensing tank. The only one that beat all of it's standardized tests under all conditions was a (definitely not cheap!) stratified condensing tank (heater #5).
I kinda wish they'd tested at least on of the standard-efficiency tankless units in this comparison, but it is what it is. The low mass of a tankless keeps it from falling off a cliff the way tanks do under low use conditions, but the low-use profile they used has a larger fraction of the total test volume in draws under 2 gallons (where tankless performance gets killed)- I suspect a standard efficiency tankless would have a similar degradation to the condensing tankless- subtracting 5-8% from the condensing version's performance is probably reasonable, meaning that in heavy use it'll be in the low 80s, moderate use around 75-78%, and low use around 70%- still better than the low-tech tanks under their best-case heaviest use.
The tank heaters DO fall off an efficiency cliff! None of the non-condensing standard-efficiency tanks (heaters 1-3) tested actually met their EF numbers in moderate-use profile, although they beat their numbers in heavy use profiles. If you're an on-the-go 1-2 person family that often takes weekends away (or only bathes once/week) the tankless is a far superior option. But the stay at home family doing 2 loads of laundry every night after the kids go to bed will still see an efficiency gain with a tankless, just nothing like multiplier the on-the-go single/couple experiences.
So, it kinda depends- if you're on the go, living alone (or a water-sparing couple), often take weekends away etc, you'll likely meet or beat your tankless EF numbers by a few percent, but won't even come CLOSE to your tank's (lower) EF numbers. If you're a mostly stay at home family of 5 you'll likely meet or exceed the EF numbers for either, and the Consumer Reports analysis could be correct, but is it? No way to tell- the don't specify price & inflation assumptions. But check your actual fuel costs- they vary considerably with location. Here in MA we pay 2.5-3x the rate for natural gas as they do in UT.
For as-used efficiency comparisons, gas-fired tanks are all about maximizing the total consumed volume. If that's you/yours, great. But if its not, your actual efficiency isn't anywhere NEAR what the nameplate or EF number say. Getting efficiency out of a tankless is only about minimizing the number of very-low volume draws.
But the real reason to go tankless is to save your marriage- you never hear the screech from your spouse about the cold shower (did they factor in the cost of a divorce in the financial model for the tank? :-) )
In the Consumer Reports article they deftly dances around the longevity & service issues too- they didn't add in a full -replacement of the tank heater, simulate only an 11 year use (by excessively hardening the water- which is also a dubious method) yet say it "can take up to 22 years to break evenólonger than the 20-year life of some model". In my accounting book I'd have to double the purchase & installation costs of the tank, yet apply only a 1.25 multiplier to the tankless. Tanks RARELY give 20+ years of best-efficiency service before out & out replacement replacement is required whereas tankless burners are easily serviceable (even heat-exchanger replacements), and the bulk of the "extra" installation costs are presumed electrictal outlets for the powered venting & controls and presumed gas line capacity upgrade. A full replacement of the tankless after 20-25 years of service won't be NEARLY the numbers quoted, since electrical power, gas lines & stainless flues etc. would already be in place- it'll be about the same as the tank. In many instances the gas lines might already be big enough to deliver, needing no upgrade.
It's true that while it's easier to service, the tankless will likely NEED to be serviced at least a couple of times in 20 years (I've got one that's 15 years old and going strong without any service beyond brushing out the heat exchanger once, but it's less complex than the Noritz & Takagis they tested). But then again, is swapping anodes every years and annually draining sludge from your tank really less work than swapping filters & occaisionally checking for lime scale on the tankless, cleaning as-necessary? It's a crap shoot, sez me, but in most situations the efficiency of the tankless will be better. Whether it ends up being totally dollars & cents cost effective is something you'd need to analyze, but I've yet to hear from anybody who went back to a tank after living with a tankless.
If you're considering it ever, PLEASE do a better job of the analysis than the Consumer Reports folks, eh? They adequately explain neither their test procedures nor their financial analysis, projected fuel prices, etc.. I found the article pathetically devoid of essential detail, and high on "we know better, and thus recommend..." attitude. (Can't say I'd recommend buying their mag, eh? But I s'pose I'm just coppin' an attitude myself. ;-) )
...there's another FAR better option for many:
If your space heating system is done with a mid-efficiency (83%+) or higher hydronic (pumped hot-water) boiler, an indirect-fired HW heater running off the boiler will give you similar performance for less money, without the cold water sandwich. Done right, it should be capable of keeping up with continuous-demand of back-to-back showers (even with guests), just as a tankless would. And by increasing the duty-cycle of the boiler, it would improve the overall heating-system efficiency.
Standby losses of an indirect are far lower than that of a selfstanding gas fired tank, since the plumbing penetrations are small so it can be fully & insulated (the selfstanding has flue & burner penetrations & clearances to contend with) it doesn't have a flue to convect heat out of the tank 24/7, or a pilot light burning 24/7 (literally half the gas consumption of the heater for many 1-2 person families.)
Indirect fired tanks off the hydronic boiler is THE way to go whenever it's an option. Beyond that, you'll get better performance out of an on-demand. If the cold-water sandwich is too much of an annoyance, there are moderate-cost adder ways around that too:
At least? Did you happen to forget that the mfg of just about all product require annual deliming/descaling of the compartment? Shorter timeframes if the water is really hard?
You're implying to put it in and forget it, just like tank water heaters. People treat their plumbing just like that, and they are surprised when I tell them the tank needed to be drained once a year.
With this being known, and a tankless in a "have to" situation in order to provide the hand crossing the flame speed in heat transfer,
you're sending an incorrect message to the majority to think that this product offers such reliability.
If it did, there wouldn't be so much discussion as to "should I" without considering the variables.
You seem knowledgeable about the product and quick to defend it. Are you in the United States,
and are you in a warm climate area where these devices can be mounted outside, or have a less than 40 temp rise to overcome.
Where's Master Plumber Mark and his tankless experiment on the gas savings we used to follow...
They are here. Poeple are buying them. I doubt like hell they are going to go away anytime soon but dollar for dollar they are a huge waste of money. Not worth the argument.
At .70 EF standard tankless thats =528000 btu = 5.3 therms.
At .45 EF tank = 821333 btu =8.2 therms
Difference =8.2-5.3= 2.9 therms a month. I pay 95 cents a therm, so a savings of $2.75 cents a month. That tankless will pay for itself in no time.
I have an older ELM Aquastar 125VP. Incoming water temperature is about 40 degrees, and that means a temperature rise of 80 to 90 degrees at this time of the year. The unit is rated for 2.09 gallons pe minute with a 90 degree rise.
The other day I measured the rate of water use that I used while taking a shower. The rate of water use during the shower was 1 gallon per minute and about 1/3 of that was from the cold water mix.
Unless you are taking 2 or 3 showers at the same time, a gas tankless works just fine even with cold water coming in!
More like a 90 degree temperature rise at this time of the year (in MA).
Your cost of gas is low. My per therm cost is $1.24240 per therm for cost of gas, plus $.54100 per therm for distribution charge for first 50 therms, and $.24660 for each therm over 50. Then there is the distribution adjustment charge of $.01128 per therm.
My gas total is a minimum of $1.50 per therm for the cost of gas during winter heating months, and and around $1.80 per therm during low use months.
Using the EF numbers to calculate anything it a grotesque distortion. EF testing involves 6 equal draws of 10.7 gallons one hour apart which exactly how NOBODY uses water. The test is currently undergoing revision- expect a new, if not necessarily improved version by 2010. The testing by PG & E was part of an attempt to rationalize/harmonize the subsidy incentives based on EF numbers, etc. It basically proves that the EF test as currently implemented isn't up to task of determining true efficiency.
If the tank's effective efficiency is .45 for a 28gallon a day profile, that's true on average efficiency only if that much is used EVERY day. My "on the go many weekends away" intermittent singles/couples users will see much lower efficiency than even the 28 gallon daily use profile indicates unless they're religious about turning the HW tank off every time they head out for more than 24 hours. But their tankless efficiency will remain the same no matter how intermittent their use is.
[Edited to add] If the tank has a standing pilot it'll usually be burning somewhere between 5-10 therms/month. When the tank is actually in use, some of that heat goes toward temperature maintenance and not fully wasted. But for the "weekends away" intermittent user figure on at least 1/4 therm+ thrown away for every full day that you're off skiing, gambling, at the beach whatever. Depending on standby flue losses (bigger on atmospheric drafted tanks than forced draft versions) and how well insulated the tank is, that easily climbs to a half-therm/day and higher. The ~3 therms/month cited for the 28 gallon/day profile is underestimating it by at least half for the weekends-away crowd.[end edit]
The purely economic arguments for/against tankless have many assumptions (few of which were indicated in the Consumer Union report, which was also based on a testing profile MOST favorable for the tank.) Anyone doing it purely for economic reasons needs to do their own math, based on their own assumptions, use patters, fuel costs, and the CU report didn't provide even a hint of a framework from which readers could make an informed estimate. From a convenience & creature comfort "installation costs be damned" point of view, I've yet to encounter anybody who SO disliked the quirks of a tankless that they ever went back to a tank. (I'm sure there are some counterexamples to prove the rule, but they're rare.)
Another assumption often built into the arguments is that use profiles will remain constant independent of heater type. But the endless shower just isn't possible with a tank, and many end up using more HW when a tankless is installed. But due to the inherently higher efficiency that rarely results in an actual increases in fuel use.
I'm not a huge advocate of standalone tankless HW heaters on the economics alone, but I found the CU report to be SO sketchy and misinforming (based on what academic & utility company studies have shown, forget about the DOE's EF numbers) that I felt compelled to spell it out a bit better. I AM an advocate for low temp hydronic heating and indirect-fired tanks, where true gains in efficiency (measured as significant reductions in fuel use) can be made. In low heat load homes (most of the 2000' or smaller homes in the US would qualify), using a tankless as a low-mass modulating boiler in a combi HW system costs about the same as a cast iron boiler + indirect tank, but can be designed to run significantly more efficiently (with sub-140F water.) It won't be as efficient as a modulating/condensing boiler, but it won't cost as much either- it's a middle-ground approach. In practice it'll beat most single-stage condensing gas furnaces + gas-fired tank.
Variations on the the theme are currently being studied by utlities in California and Canada (eg, the eKoComfort comparison paper), and in the next couple of years there should be more published data on particular configurations. In eKoComfort combi comparison the unbuffered air-handler coil running off the tankless beat the tank combi system by about 10% in overall fuel use- about 1.5-2x what the raw combustion efficiency numbers might have indicated (and a heat/HW combi is by far a best-case absolute highest duty cycle use that a tank heater could achieve.) In a buffered tankless scenario, the tankless would cycle longer and far less often, reducing wear while improving net efficiency over coil-in-air-handler system.
Last but not least, presuming that a tank in an "install & forget" setup will be running anything like it's (already paltry) new-unit efficiency is another bad assumption too. Annual or seasonal purging of the sludge settled in the bottom is required to keep the heat exchange coefficient from suffering, as well as swapping out sacraficial anodes every few years. Hard water de-scaling is usually only a problem requiring anual maintenance for tankless systems in areas with actual high hardness. Most municipal systems are chemically buffered sufficiently that it can be put off for 3-5 years, or until there's a noticable drop in output. (I've seen one tankless system that went 15 years without de-scaling or any service whatsoever, and it's still in service. I've yet to see a neglected tank last that long, but I'm sure there are a few around.) All gas burners need maintenance.
I'm not anti-tankless, everyone needs to crunch their own numbers. I'd have one if I had a big whirlpool tube I needed to fill. I don't think one size/type fits all works for WH. Tankless are great in the southwest, where they are mounted outside and have warmer water temps. AC heat recovery is great for south florida. A boiler system is great for the Northeast. Tank units may be best in the midwest. Electric units may be better if you only other options is propane. Drain heat recovery may be viable depending on you use profile. Solar can be an option for some. Heat pump recovery, etc. I'm just skeptical when anyone only recommends one solution and don't now the particulars for a specific case.
At the end of the day, everyone needs to do their own research and find the solution that best fits their needs. If your dependent on plumbers for your plumbing needs, your local plumbers will greatly impact the economics of your decision.
Crunching number does not apply when considering what my needs were for a household of 6. Tankless WH provided the needs for our family.
The majority, and people who buy these units?
Never drained their water heater once a year.
Explain how the thinking will now change on these matters.
I defend my own statements because I have hands on plumbing products every day, and people do not understand that these devices are not a put-it-in-and-forget-it mentality.
That's why I come to the plate on these discussions because the "average" homeowner, the "majority" that use nearly "all" plumbing systems are not going to have the insight like a select few of you crunching therms and showing $2.75 savings like it was a free 2 liter of pop at the local convenient store.
The reality is maintenance is the key to run these devices, when they malfunction like they will, they are expensive and the average customer isn't going to understand "clean flow switch screen" or know how to troubleshoot a code error on the digital touchscreen on the unit.
You can information overload the internet with tankless treats, but the average consumer is forced to call a plumber OR tech support to get their hot water back.
The basic of idea of creating hot water just got more difficult, not simpler. That's not to say that tankless won't have its place in America, it will.
Anyone who buys one of these is a daredevil right now since the odds are against them that their neighbor has one, and someone knowledgeable is right there to fix them when they break, immediately...
not hours I'm speaking of, days. Do you know what it is like to be without hot water for days?
What happens if a certain "part" costs more than a tank heater to replace? Now you're faced with a device that in average thinking, a tank heater for less as a whole looks pretty darn inviting from that aspect of keeping money in your pocket.
Isn't that what this product is all about, keeping money in your pocket?
IF you pay a plumber annually to correctly delime/descale these units according to mfg. specs, call on them to fix every malfunction these units have over the course of time, there are no numbers you'll ever produce that states in legitmacy that the cost outweighs the performance value. Never.
Anything mechanical can and will fail. A retrofit to a newer model won't allow a reconnect to the existing stainless steel flue, it will void the warranty even though it is the same damn thing.
These are all "charges" that get way-layed into the customers back pocket, all the while the plumber is making a mint on the green idea.
Why is it that a tank water heater after initial heat up can maintain ready to use hot water for days, on just a standing pilot alone? Or are you going to tell me that the cost of that flickering match flame is ungodly expensive and horrible in gas consumption.
There's lots of observants that follow my thinking when I type on the internet about these products. They might not ever put their voice to print, but I think they understand that I'm pointing out some very credible points of interest in the concern of going after new ideas that can have one simple common issue, cost.
So as a troubleshooter as a service plumber constantly working on products such as these, understanding the ins and outs of how things work,
You provide the positives and I'll provide the actuals. I think that's a fair and balanced approach to any time someone cheerleads something that in actual time span is going to have to realize that there's hidden costs to when plumbing attacks.
What percent of the population has ever measured the amount of water used per minute for their showers? That would be just about 0% if you ask me. The other day I measured my flow rate for the first time ever. 1 gallon per minute works just fine.
The mandate for shower heads is 2.5 gal/min MAXIMUM. You are allowed to use less than that flow rate. Also, 100% of the water used is not hot water. You should measure the actual amount of water that you use in shower before you throw out numbers!
The average shower temperature does not mean anything. Water has to be heated to well over 105 degrees to fill a tub with 105 degree water in the tub. When you take a shower, you mix hot and cold water together to get 105 degrees. Your calculated temperature rise is low, and your hot water volume used per minute is high.