Tankless - is it worth it?

I'm seeing mixed reviews on tankless systems. After a very aggrivating day dealing with the pilot going out on our whirlpool water heater we're deciding whether or not to just replace the whole thing b/c we actually have a black spec (that smear) issue that we can't get rid of.

As mentioned in other forums, we've already replaced the expansion tank, anode rod, PRV and we don't have flex hoses going to the tank.

I spoke with two different plumbers today. Both recommended replacing the hot water heater all together, but one was in favor of a tankless to resolve our black spec issue. The other didn't really have an opinion one way or another but he as well as the other claimed that it's possible that replacing the water heater for another tank-based heater may not resolve our issue.

The plumber who recommended the tankless felt that the tank-based heaters would continually hold these black specs in the base and after time they would eventually return no matter how many times I flushed the system b/c it would just settle at the base.

Makes some sense, but honestly, I don't know anything about hot water heaters let alone tankless.

My parents installed one in their home a year or so ago and seem to be happy. But they had a small space to deal with and the house is kind of small.

Thoughts?

Depends on the costs of your options and how you weight various aspects of ownership. Changing the installation will depend on what you have to do for venting of the tankless and/or any line size changes.

How much gas do you use each year for water heating? You can use that and the rated efficiency of your water heater in order to determine how much you might save with a higher efficiency system.

You can use the difference of installed cost then divide by the annual energy savings to figure the payback in years.

Of course there is no guarranty that either solution will eliminate the specs.

how much $$$$

if you simply change the heater and put in a new one odds
are you will win for around 750



if you go to a tankless you might win there too but the price is going to be ....what did he quote you....$3500????



do the math...... its your gamble....

I would rather gamble for 750 and be wrong than $3500
and still lose......

If you want endless hot water, go tankless, but it's not necessarily lower-maintenance than a tank. It WILL be higher efficiency than a standard tank, but not by quite as much as the EF test numbers might imply for most users. For low volume or intermittent users it'll be twice as efficient as a tank, but for high volume users (think 8 showers/day) the difference is relatively small.

If you have a hydronic (forced hot water) heating system, an indirect-fired tank running off the boiler will be higher efficiency than a tank, with quicker recovery times delivering similar or higher efficiency than a standard tankless for less money, less maintenance & fewer quirks. An indirect will usually outlast a tankless- in most cases it'll be the last hot water heater you ever buy.

Folks are quite polarized on this topic. Research has proven repeatedly that you will spend more for tankless over the years than for conventional tanks. The "endless" hot water is pretty much a myth in many cases. There are many factors to consider including incoming water temperature, especially in the winter, cost to increase the gas or electric service, mineral content of the water, qualified servicemen in the area (they do require frequent cleaning) and the initial cost of the unit. There is a considerable time lag from the time you turn the faucet on until you get hot water and unless you turn the faucet on fairly strong, you may not trigger the unit to light.

You big problem right now is that you have the worst water heater on the market. There is a whole thread on this forum devoted to Whirlpool problems. My advise is to swap it out for either a GE/Rheem or Bradford White.

"The "endless" hot water is pretty much a myth in many cases"

A myth? I don't understand your choice of words. If you turn the hot water faucet on and it delivers hot water till you decide to turn it off whether it be 5 minutes or 5 days, isn't that endless?

zl700 said:

"The "endless" hot water is pretty much a myth in many cases"

A myth? I don't understand your choice of words. If you turn the hot water faucet on and it delivers hot water till you decide to turn it off whether it be 5 minutes or 5 days, isn't that endless?

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Well,


Depends what flow rate you decide is feasible when that "endless hot water" is delivered from unit to tap.


The price enticing doesn't reveal those performance curves on the lower priced models.

Throw 3 fixtures on demanding hot water and now you have problems...if you didn't buy the top sized model. Trying to expect that from the curious won't happen.

foxhome01 said:

Thoughts?

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We just installed a tankless - here are my thoughts:
1. There is a lag - in our case it is exacerbated by an over long pipe run but there will always be a lag. The flipside is that we waste no energy when not using hot water. Our old tank would heat water even when we didn't use it.
2. The water is never scolding hot (but some installers may increase the temperature above code if you ask). This means dishwashers and laundry (if you use a hot cycle) may not be as effective but it also means you don't burn yourself by accident.
3. Running costs are substantially less - almost one third but we haven't gone through a winter yet. But capital costs after subsidies will take 15 years to break even.
4. The tankless takes up no space (it is tucked behind the furnace) - this was what swayed it for us - we wanted the space the tank took up.
5. Hot water is endless - it really is. Of course you have to size it properly - just as you do your tank. In exceptional circumstances when every hot water faucet/device is placing demand then the tankless will be just as ineffective as a tank. In normal usage with our tank we would "know" not to try to have 4 showers in succession whilst running the dishwasher - now it doesn't matter, every one gets up and showers regardless of how many people have already done so.
6. Hot water from the tankless is potable - we do use it for the kettle and cooking and it "feels" like water boils faster and saves energy but of course it takes time for the faucet to deliver hot water and this consumes energy so I've no idea if there really is a net benefit.
7. I believe tankless is "greener" but I have no real evidence for this.

Conclusion: I wouldn't buy a tankless unless the space issue was important. Apart from the inital outlay and the lag I've no regrets going tankless.

There just aren't a whole lot of savings to be had in tankless vs. storage to justify a large price differential. A retrofit adds substantial cost because of the necessary vent changes compared to a ~40,000 Btu/hr non-condensing burner. An efficient non-condensing tank will run about 227 ccf/yr by the energy guide while the best of the tankless will run 158 ccf/yr (and I have serious doubts about the relative rating as it seems to use a non-derated AFUE that just isn't realistic for the real world, 98%.) The difference of 69 ccf/yr works out to about $69/year for me. So I could justify about $700 installed cost difference realistically. Except for one problem: I'm using much less than 227 ccf/yr already with a relatively inefficient tank (only 0.58 EF.) In fact, my family of four's use is less than the Energy Guide rating of the best rated tankless already. If I netted 50 ccf/yr or $50/yr with the best tankless vs. what I have now I would be surprised.

There is only one thing I really could use the limitless hot water for, and that is a large tub. I can already run two showers, a dishwasher and a clothes washer simultaneously on my 50 gallon tank. But the tub takes a lot more hot water than those four combined, so I have to do a big pull, followed by a second small pull when the tank recovers about 15 minutes later.

I am concerned about maintenance issues with a tankless (although FVIR has made formerly troublefree gas operation problematic.) But I'm more concerned about uneven temperatures, particularly at low flows. I really don't want a fussy system.

The other thing I like about a tank is that if I lose gas, have trouble with the burner controls, or more importantly if I lost electric I've still got a tank of hot water without needing a generator to run it. The non-electric side of it has been useful in ice storms where power was out for 3-4 days. The tank of hot water came into play when I had burner trouble. Two of us took turns showering at 2.5 gpm and still had so much hot water left in the tank at 120F that we were looking for ways to use it before I dumped the tank to drain the gas control valve. And it had already been out for 12+ hours since I knew when the pilot was last operational.

Thank you everyone for your input. At the end of the day we probably would prefer to just replace with a good quality tank. BUT...we're really trying to find the silver bullet that will eliminate our black spec issue. Unfortunately, neither one seems to be providing a guarantee.

A suggestion was made to replace the tank with a quality tank and perhaps put a filter on the hot water line leading from the tank to the house and b/w the combination it may eliminate our issue. Unfortunately, the plubmer who made that recommendation had never done that before and isn't sure it's doable.

We've thought about a whole house filtration but since we only see these from the hot water, we think it's not worthwhile to install a whole house one.

Anyone have experience with putting a filtration system on the hot line from the tank to the house?

foxhome01 said:

I'm seeing mixed reviews on tankless systems. After a very aggrivating day dealing with the pilot going out on our whirlpool water heater we're deciding whether or not to just replace the whole thing b/c we actually have a black spec (that smear) issue that we can't get rid of.

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Have you determined what is the cause of the black speck? if not perhaps a sample of the water sent to a test lab may be able to determine the cause if all other methods have failed. Then perhaps you can decide which option to replace is best for you. If you have room for a tank then it is the better option to go for energy efficiency wise. fwiw

flamefix said:

Have you determined what is the cause of the black speck? if not perhaps a sample of the water sent to a test lab may be able to determine the cause if all other methods have failed. Then perhaps you can decide which option to replace is best for you. If you have room for a tank then it is the better option to go for energy efficiency wise. fwiw

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We have and it was originally thought to be rubber but the City (who tested it) wasn't able to draw final conclusion b/c although it "acted" like rubber the checmical make-up wasn't matching up. I'm looking into seeing if I can get someone else to test it.

Gary Swart said:

Folks are quite polarized on this topic. Research has proven repeatedly that you will spend more for tankless over the years than for conventional tanks. The "endless" hot water is pretty much a myth in many cases. There are many factors to consider including incoming water temperature, especially in the winter, cost to increase the gas or electric service, mineral content of the water, qualified servicemen in the area (they do require frequent cleaning) and the initial cost of the unit. There is a considerable time lag from the time you turn the faucet on until you get hot water and unless you turn the faucet on fairly strong, you may not trigger the unit to light.

You big problem right now is that you have the worst water heater on the market. There is a whole thread on this forum devoted to Whirlpool problems. My advise is to swap it out for either a GE/Rheem or Bradford White.

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OOooh reasearch- my cuppa tea!

References?

Runs with bison said:

I'm using much less than 227 ccf/yr already with a relatively inefficient tank (only 0.58 EF.) In fact, my family of four's use is less than the Energy Guide rating of the best rated tankless already. If I netted 50 ccf/yr or $50/yr with the best tankless vs. what I have now I would be surprised.

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I'm surprised that you separately metered your HW heater in order to obtain this data(?).

Runs with bison said:

The other thing I like about a tank is that if I lose gas, have trouble with the burner controls, or more importantly if I lost electric I've still got a tank of hot water without needing a generator to run it. The non-electric side of it has been useful in ice storms where power was out for 3-4 days. The tank of hot water came into play when I had burner trouble. Two of us took turns showering at 2.5 gpm and still had so much hot water left in the tank at 120F that we were looking for ways to use it before I dumped the tank to drain the gas control valve. And it had already been out for 12+ hours since I knew when the pilot was last operational.

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There are plenty of atmospheric-drafted tankless units with standing-pilots or water-flow powered ignition out there that run just fine without power. The pilotless no-power-required Bosch P1600H even has an EF of 0.80- barely under what it takes to qualify for tax credits & rebates, etc. (IIRC the propane fired version has an EF of 0.84, so it probably DOES qualify.) You don't need a tank to get t features. What most of those DON'T get you is dual-shower use in coldwater areas- it's just not enough burner. But for 1-shower homes/condos/cabins it's a very space-efficient (and fuel-efficient) option. Of course it still has most of the usual low-end tankless issues, but it's still good enough to recommend (or at least nobody's come after me to complain about it.... yet. ) It's an improvement over it's ELM Aquastar ancestors by most measures, but it retains a family resemblance under the hood...

Of course, if you lose gas you're still stuck... (but power loss is a far more likely/frequent scenario for most.)

Dana said:

I'm surprised that you separately metered your HW heater in order to obtain this data(?)

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While it would be more accurate (and indisputable) it is not necessary for getting a good estimate. My natural gas use is solely for hot water for 5-6 months of the year and I'm now in the 10 ccf/month range--with about 3 ccf/month of that being storage losses. This gives me the baseline water heating cost in warm months. Some adjustment is then needed to account for seasonal differences when home heating is occurring.

I've measured storage losses during an extended vacation with the water temp set point unchanged. Since the tank is in the same interior space with the HVAC, the surrounding room temps I've measured are surprisingly similar in both heating and cooling seasons. This allows me to subtract storage losses directly. Alternatively without measuring them, they could be estimated through back calculation from the AFUE and energy factor.

From there it's a matter of adjusting the remaining gas use for the delta between heating and cooling season water supply temps for the other months. This is a large factor (it adds over 50% in the heating months by my estimation.) For us the major use is showers so I apply the factor to all of the hot water demand. There is not only an increased duty for heating the water, but more hot water is required to acheive the same shower temp at a given total flow, because the cold water mix is even colder.

My present water heater nat. gas use estimate is about 144 ccf/year.

Runs with bison said:

While it would be more accurate (and indisputable) it is not necessary for getting a good estimate. My natural gas use is solely for hot water for 5-6 months of the year and I'm now in the 10 ccf/month range--with about 3 ccf/month of that being storage losses. This gives me the baseline water heating cost in warm months. Some adjustment is then needed to account for seasonal differences when home heating is occurring.

I've measured storage losses during an extended vacation with the water temp set point unchanged. Since the tank is in the same interior space with the HVAC, the surrounding room temps I've measured are surprisingly similar in both heating and cooling seasons. This allows me to subtract storage losses directly. Alternatively without measuring them, they could be estimated through back calculation from the AFUE and energy factor.

From there it's a matter of adjusting the remaining gas use for the delta between heating and cooling season water supply temps for the other months. This is a large factor (it adds over 50% in the heating months by my estimation.) For us the major use is showers so I apply the factor to all of the hot water demand. There is not only an increased duty for heating the water, but more hot water is required to acheive the same shower temp at a given total flow, because the cold water mix is even colder.

My present water heater nat. gas use estimate is about 144 ccf/year.

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I tend to believe numbers far more when it's actually measured rather than inferred- it's quite easy to fool oneself (I've fallen into that trap innumerabley times.) You are likely be underestimating by quite a bit:

Measurements in a state-wide study by PG & E in California in 2004-2005 showed that average energy use for heating hot water in January is about 300% of July usage. (This will surely vary by user, climate, and water distribution system, but bear in mind this was an average- some had to have shown an even wider delta.) In fact, the total energy used for hot water for the 6 months of May-October was less than half that of 6 months of November-April. In other words, winter use showed an average increase of over 100% of the summer average, not merely "...over 50%..."

Reference:

http://www.pge.com/includes/docs/pd...advisorygroup/pagetteupdate_water_heating.pdf

(See the bar graph on p.8) I have a 93 page summary of the study behind that on file if you're interested (seems it's no longer available online.) Winter time hot water use in the study was slightly higher in the winter months, but nothing like the difference in energy use.

Short of actual measurement, you probably need a better model for the estimate. Using the PG&E data for a model, 50% more energy use during the 6-7 months of heating season would be a huge undershoot- a 100% boost in the monthly average would be more likely.

AFUE & EF are horribly flawed tests- no better than educated guesses when applied to actual as-used efficiencies & measured fuel use, and would be an even lousier method for estimating. With AFUE it's a matter of how well matched the burner is to the actual load and whether short-cycles can be prevented. With EF it's all about volume of use when it comes to tanks- if you use more than the ~62 gallons/day you beat the EF numbers, if you use less, you get less (often FAR less) efficiency. With a tankless it's more about the volume per draw- short-cycles kill efficiency pretty fast, but shower-length draws meet/beat the EF numbers. Even a 0.66EF induced-draft electronic ignition tank drops below 50% efficiency when the daily draw drops to under 30 gallons. A 0.90EF condensing tankless drops to under 80% average efficiency under predominantly short-draw use profiles. An average use scenario for a tankless roughly equals a best-case high-volume scenario for a standard tank, but the worst case low-volume use scenario for a tank is off an efficiency cliff.

Reference:

http://www.aceee.org/conf/08whforum/presentations/1a_davis.pdf

(Compare heater 3 on page 9 to heater 6 on page10. We can reasonably assume a standard efficiency 0.80-0.84 EF tankless will perform about 5-10% worse than the 0.92EF condensing tankless tested, heater #6. The short-cycle losses of a standard tankless will be about the same as a condensing version, but during long draws the condensing version would pull ahead.)

If most of your hot water volume is indeed showers, you can get fairly decent payback with drainwater heat recovery systems. If the price of natural gas keeps crashing it'll be hard to rationalize as a retrofit, but for many/most it's a far more cost-effective upgrade than even subsidized solar hot water. It will likely beat your 401K or other stock portfolio after-tax performance though (In new construction with combined heat/hot water systems it can often pay back half up-front by being able to downsize the boiler.)

Since you are getting a new hot water heater maybe you should think about getting a solar panel to heat the water. I have talked with Solar Tek and had them give me a price. It is expensive up front, but in the long run you will save money. And, it is a true hot water heater not a tank less system.

Dana said:

I tend to believe numbers far more when it's actually measured rather than inferred- it's quite easy to fool oneself (I've fallen into that trap innumerabley times.) You are likely be underestimating by quite a bit:

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Doubtful as there is more calculating and measuring than "inferred" implies. I've accounted for and measured most of the key differences (ambient room temp, seaononal incoming water temp), plus I've made conservative assumptions (relying on the higher demand of the winter mix.) I don't have external envelop lines, tank, or recirculation, and my tank is located in the basement center of the structure. I've insulated about 75% of the linear feet of my hot water lines.

If I had a spare gas meter about I would install it for a mid-winter measurement. I do, however, intend to do some retests where I can during mid-late winter when the ground is at its coldest. If I'm appreciably off, the results will show it.

In other words, winter use showed an average increase of over 100% of the summer average, not merely "...over 50%..."

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Reality check: the basis of their midpoint is unlikely to be anything resembling my own from what I can see in their numbers and my own usages over various years. In fact, it wouldn't even hold for the electric water heater in my previous home. If it did the winter electric use would have spiked like summer and exceeded my total actual electric use each winter month. They are so far off of my usage profile it's not even funny.

That isn't only true for this home and the last, but also the three prior to that. If I used their 300% factor then it appears I didn't use more than a tiny amount of gas for the furnace in those homes in the coldest months--actually most months the furnace would have had to be producing gas to run the water heater.

As it is, I can do actual measurement during some milder weather stretches during mid-winter when the furnace won't cycle, so I'll see. It won't effect the supply water temp much as the ground temperature and reservoirs don't change temp that rapidly. Should make for a nice averaging effect.

AFUE & EF are horribly flawed tests- no better than educated guesses when applied to actual as-used efficiencies & measured fuel use, and would be an even lousier method for estimating. With AFUE it's a matter of how well matched the burner is to the actual load and whether short-cycles can be prevented. With EF it's all about volume of use when it comes to tanks- if you use more than the ~62 gallons/day you beat the EF numbers, if you use less, you get less (often FAR less) efficiency. With a tankless it's more about the volume per draw- short-cycles kill efficiency pretty fast, but shower-length draws meet/beat the EF numbers. Even a 0.66EF induced-draft electronic ignition tank drops below 50% efficiency when the daily draw drops to under 30 gallons. A 0.90EF condensing tankless drops to under 80% average efficiency under predominantly short-draw use profiles. An average use scenario for a tankless roughly equals a best-case high-volume scenario for a standard tank, but the worst case low-volume use scenario for a tank is off an efficiency cliff.

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Compared to those California numbers they appear extremely accurate. I'm not seeing a burn efficiency cliff in my summer gas use. Instead it is tracking with hot water use reduction and the fixed storage loss that I measured and already factored in. Actually, if you look again at the water heater testing, you can see that it agrees with what I'm seeing. His EF conclusion leaves me with a big, "Duh! You didn't have to do any testing to determine that, it's first principles." Storage losses are essentially fixed, and don't scale with use. That's why you subtract them out and use some approximation of the burner system AFUE...essentially what I'm doing.

One of the things I've learned over the years is that estimating with reasonably thought out engineering models works even when I expect poor results. I've not had trouble matching up my water use, gas use, or electric use within about 10%. When I'm off by more than that, I try to determine why and adjust.

The problem with the highlighted part above is that it would counteract the very effect you are claiming I am undercounting. Winter will demand longer, harder burns with a better (colder) initial profile. Thermal efficiency would increase rather than decrease. This would dampen the other weather impacts. (Raising summer use, reducing winter compared to fixed efficiency.) No doubt the efficiency impact is real, but it is not a major factor compared to things I am already accounting for.

Continuing with the AFUE analysis you gave above, one wouldn't expect a tankless unit sized for multi-point operation to be efficient with my typical shower draws. Half of them are near the limit of where the tankless even turns on.