Tankless info from consumer reports, Tankless...Bahhhhh

Discussion in 'Tankless Water Heater Forum' started by nhmaster, Dec 29, 2008.




  1. 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...
  2. nhmaster

    nhmaster Master Plumber

    Messages:
    3,189
    Location:
    S. Maine
    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.
  3. chris8796

    chris8796 New Member

    Messages:
    100
    Location:
    Illinois
    If you follow the low use profile, 28 gal a day, that is 28g x 30 days x 8.8 lb/g x 50 F temp rise = 369600 btu/month.

    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.
  4. Ladiesman271

    Ladiesman271 Homeowner

    Messages:
    221

    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!
  5. Ladiesman271

    Ladiesman271 Homeowner

    Messages:
    221


    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.
  6. Dana

    Dana In the trades

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    2,812
    Location:
    01609
    You currently pay a only bit more than half what folks in New England are paying for NG (59% of what I paid on my last bill in MA, and I'm in the cheap-zone of New England). If you anticipate only paying $0.95/therm from now until 2025 I suspect you're being a bit optimistic in your assumptions...

    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.
    Last edited: Jan 15, 2009
  7. chris8796

    chris8796 New Member

    Messages:
    100
    Location:
    Illinois
    A gallon a minute is admirable, 90+% of the population would not want a shower at 1 g/min. Most people demand 2 g/min shower and shower heads are mandated to be 2.5 g/min.

    The calculation was an average, my annual average cold water temp is 55 (today it is probably 40!, upper midwest). The average shower temp is 105, hence a 50 degree rise.

    My gas company charge a flat customer fee and a meter fee with a PGA charge and dist fee. The pga and dist fee equals 95 cents a therm. My gross costs are higher if you incorporate the fixed fees, but don't apply in this comparison.

    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.
  8. gregsauls

    gregsauls Homeowner

    Messages:
    56
    Location:
    Texas
    Crunching number does not apply when considering what my needs were for a household of 6. Tankless WH provided the needs for our family.



  9. 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.
  10. Ladiesman271

    Ladiesman271 Homeowner

    Messages:
    221

    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.
  11. chris8796

    chris8796 New Member

    Messages:
    100
    Location:
    Illinois
    Dana,

    Oddly, I don't think we are too different in our opinions. We both appreciate either side can easily manipulate the numbers to justifiy their case.

    I like the idea of a better "overall" solution. The combi approach is interesting. I would like to see more solar thermal applications and I can see how you could intergrate with this approach. I think a major stumbling block with solar WH is the cost to garuantee constant hot water. A solar water heater could provide 90% of your HW needs but that last 10% will cost you. Either in capital (Tankless) or standy loses with a tank heater. If you could have a combi system that could easily incorporate thermal solar plus with some heat storage options, it becomes attractive in overall energy use.
  12. chris8796

    chris8796 New Member

    Messages:
    100
    Location:
    Illinois
    They don't have to measure it to know it is too weak for thier liking. I have taken a 1 gal/min shower (thanks to galvanized plumbing) and know it is weak. It may be normal for you, but the vast majority of Americans would be disaapointed with 1 g/min
    I have measured mine, 2.2 g/min, not bad-not great as showers go. I've measured the hot water temp, the cold water temp, the drain temp and the drain temp after the drain water heat exchanger. So I'm not a novice on the topic.


    The energy use is the same for calculation purposes. 50 gallons at 100 F requires the same energy whether you heat 50 gallons from 50 F to 100 F or you mix 25 g of 150 F water (orig 50 F) with 25 g of 50 F water. The specific heat of water is fairly constant over this temperature range.
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,932
    Location:
    New England
    My winter cold water supply can and has approached 33 degrees. The most temp rise most of the tankless can provide is maybe 90-degrees. Considering it has to run through nearly 40' of pipe to get to my shower, even at all hot, there may not be enough hot for a comfortable shower - it does cool off along the way regardless of the insulation. It all depends on where you live, and your expectations. Some of the tankless restrict the flow to maintain the temp rise, some don't, and the output just gets colder making getting just the right temp nearly impossible to attain.

    I'm glad I switched to an indirect...obviously, that's not an ecconomical option unless you have a boiler, but I do, and did...much better!
  14. Ladiesman271

    Ladiesman271 Homeowner

    Messages:
    221

    That is meaningless. There are shower heads, and there are shower heads. The type of shower head makes a huge difference on what the water flow feels like when it is compared with the maximum flow rate.


    http://www.jet-streamshowerhead.net/work.html


    Around here, the state water authority went around and changed everyones shower heads to a low flow air mix type of shower head. Mix some air in with the water, and the spray feels nice and strong. I have never measured the maximum flow rate.





    There are full flow shower valves and adjustable flow shower valves. If you can't adjust the flow for comfort, then the shower head determines the flow rate. I can adjust my flow rate for comfort, then I measured the result.





    The point was you can run out of temperature rise with a tankless to make those calculations useless!
  15. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    Where is "around here" ? I'd be interested to know what State authority - US/UK other ? Frankly if I liked the shower head I'd keep it. If I didn't I'd yank it out

    We had a 30g oil fired that went & we switched to a 50g high efficiency electric - no gas to the house. We need a new boiler so I want a hot water coil i n the boiler. In the winter the boiler will run & take the load off the electric. In the warmer weather a solar heater will assist. We have about 80 psi here, pretty good flow.
    Between these 2 methods I'm hoping to cut the electric use

    It's 12 degrees out & my input Temp is around 46-48. The basement has dipped to 54 from normal temp of 58-63. The next fgew days will be even colder
    I'm not sure what the gpm is, but I've been in lower psi areas & the flow for taking a shower is poor. Some of this may have to do with the design of the shower head
  16. Ladiesman271

    Ladiesman271 Homeowner

    Messages:
    221

    Maximum temperature rise depends on the flow rate required.




    My longest run is about 60 feet and is insulated. I set the heaters thermostat for about 125 degrees measured at the kitchen sink. I have never had a cold shower. I always have to mix in cold water for a comfortable shower.

    To maintain the water temperature my particular heater uses a modulating gas burner (25K to 125K BTU) which is controlled by a thermostat that measures the outgoing water temperature. It has a fixed flow restrictor that limits flow to a maximum of 3 1/4 gallons per minute. Not sure of the maximum rise that I can out of the unit, but it is around 85 degrees right now (40 degrees input - 125 degrees output).
  17. Ladiesman271

    Ladiesman271 Homeowner

    Messages:
    221


    http://www.mwra.com/04water/html/watsense.htm


    I just noticed that the MWRA web site has a link to the toilet section of the Terry Love web site.

    http://www.mwra.com/comsupport/watersaving/toilets.htm
    Last edited: Jan 15, 2009
  18. Scuba_Dave

    Scuba_Dave Extreme DIY Homeowner

    Messages:
    885
    Location:
    South of Boston, MA
    Ah - so in MA too, we aren't in the MWRA area
    From what you said I thought it was a mandatory replacement program. It would be nice of there was a "loaner" shower head program. Take a low flow shower head home (with deposit) & try it out, if you like it keep it - if not return it

    There are still a lot of high gallon toilets out there
  19. Ladiesman271

    Ladiesman271 Homeowner

    Messages:
    221

    It was "mandatory" to a large extent. Over ten years ago they had crews go around town and provided and installed everything at no charge. I still have all of my 50 year old toilets. The MWRA installed water dams in each one of them. The shower heads are rated at 2.2 gpm or lower. They are the air mix type, so the force of the water feels higher than a standard flow unit


    Seems like the water consevation programs have helped out with water use.

    "Operation WaterSense, a joint program of MWRA and its communities, offers conservation services directly to MWRA communities. The program has helped reduce demand from 330 million gallons of water per day to 220 million gallons of water per day, and has helped residents control their water, sewer and energy costs."
  20. Dana

    Dana In the trades

    Messages:
    2,812
    Location:
    01609
    I don't think it's odd at all- we both can do the math (and probably the plumbing too. :) ) I found the CU article slanted, condescending, and unenlightening, with no framework around which people could do their own cost/benefit analyses. It was a dis-service their readership. For the strictly HW use, it all depends on how you use hot water, and what your fuel costs are (which vary by more than a factor of 2 on both axis'), and not at all addressed by the CU article.

    Many if not most newer solar heated homes are using tankless HW heaters as backup and "finish" heat for lukewarm storage, and in that application it's the right way to go. Also, more and more people are moving toward low-temperature hydronic heating in their freshly insulaton-upgraded & air infiltration upgraded homes too. When a tankless modulating HW heater's burner exceeds the house's design-day heating load by a factor of 3 or 4, using an oversized cast-iron boiler just to be able to run an indirect-fired tank isn't very efficient (still probably better than a tank HW heater + a right-sized cast iron boiler though). Utilizing a modulating mid-efficiency burner like a tankless as the combined system's heat source then becomes more cost effective up front, and significantly more efficient. With a tankless the modulation factor "right sizes" it semi-automatically to match the actual instantaneous heat load, whether the instant demand is for hot water or to run a hydronic heating zone.

    Using a low-head reverse-indirect HW heater as both the space heating buffer and the hot water heater makes for a very nice space-efficient package too. With a single buffer that all heating zones draw from/return to in place, once properly adjusted, the delta-T that the burner needs to support varies with the volume & temperature of the return water from the zones. The flame modulates up & down as the zone demands kick on & off, and only when all zones turn off and the high-limit aquastat on the buffer tank trips does the tankless flame turn completely off. This is a tried & true system architecture adapted from large building heating plants, but applied in micro-scale to micro-zoned residential structures. Actual fuel savings are usually well into double-digit percentages with this approach compared to bang-bang on/off controls.

    BTW: Many manufacturers void the warranty for tankless HW heaters used as boilers in heating systems, but I'm not sure why this should be so. If the system has even 10-15 gallons of buffering capacity the number & depth of thermal cycling will go down relative to HW use only. Takagi seems to be the only manufacturer actively encouraging combi or space heating use across their entire product line, but there are many many Rinnais and others running (off warranty) heating systems. A relative newcomer to the US market, Navien has pre-engineered some heat-exchangers & controls to make (un-bufrered) combi-system design easier: http://www.heatingbox.com/

    Navien condensing units seem to have a following among the solar-heating combi-crowd, but take "condensing" with a grain of salt here, eh? (I haven't seen any test data, but the "98% efficiency" number they tout is likely only going to hold true when the water entering the heater is well under 50F, whereas in most heating applications return water much under 100F isn't the norm. It might hit 88-89% combustion efficiency in a heating application though- better than the ~85% combustion-efficiency of a standard tankless running ~100F return water (the eKoComfort measurements). I'm not sure the condensing unit it's worth the extra money though- the difference price could buy you another 40 square feet of installed flat panel, with a bigger reduction in annual fuel use in much of the lower 48. (I'd leave that up to the local solar designer to do the math on, but it's worth asking the question at design-review time.)

    As houses become tighter & better insulated to the point where instanteous heat load far outstrips HW heater output capacity, a wave of combi systems (includting tankless HW heater types) is coming. Time will tell where the costs & benefits break down, but it's getting harder & harder to rationalize clunky oversized cast-iron boilers as fuel prices rise when low-mass modulating systems are available, and more efficient. My design-day heat load is about 30kbtu/hour, in an area with about a ~6800 degree-day climate. I could clearly run both heat & HW combi off a 199kbtu/hour in (~165kbtu out) tankless with margin to spare, getting far more use & value out of it than if used merely as a HW heater. For that matter, I could heat both my house & HW with most 50gallon gas tank heaters too (I've considered it, calculated it, modeled it, since the up front cost is SO cheap, but...), with a 10-15% comparative performance hit. YMMD.
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