Tankless Hot Water Heaters
OK, this one has me really scratching my head.
The big green selling point has always been saving storage tank losses….why heat water when you are at work or sleeping? Save energy by only heating the water on-demand…. instantaneously, when you need it. Wow, that make great sense. Sign me up.
BUT…….
Water usage–The great selling point is an “endless supply of hot water”. How is that a good “green” selling point, when water conservation should be one of our cornerstones? I own a Noritz and I can’t get my kids out of the shower! I know we waste more water, as a result waste more energy heating that water, etc. And the kids are not even teenagers yet! We need a clear stopping point….cold water! And tankless units actually have a delay in firing, where it takes 10-15 seconds for the “instantaneous” to fire and start heating the water. Storage units start delivering hot water when the faucet is turned on. Of course, both units should be used with an on-demand water recirculation pump, but that will not stop my kids from taking a thirty minute shower.
Energy Savings–On the DOE website, I saw a comparison with Energy Star storage units. They claimed that the tankless units will save approximately $100-$150 per year in energy costs. That is not a huge savings, especially when you consider the possibility of long showers. I doubt they compared longer shower times for tankless units as opposed to storage units.
Costs–Tankless units costs 2-3 times more than even the best storage units, especially when you consider the need for stainless steel flues. And they are difficult to install and more to maintain. Costs must be considered in green calculations because rarely do we have an endless budget. You could buy the best, superinsulated storage unit, insulate the hot water lines, buy an on-demand recirculation pump, low flow shower heads, and CFLs for the entire house…..and probably still have cash left for other green improvements.
What am I missing?
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Replies
I think you've got the whole picture. The only "green" way to save water heating energy is to use less hot water. Unfortunately, that requires imbuing our children with the old-fashioned ethics of forebearance and limits - and no piece of technology is going to do that. It's part of the responsibility of parenting.
You're quite right that the super-sized burners on high-volume tankless heaters make no ecological sense. In addition to initial costs and higher maintenance costs, tankless heaters rely on instantaneous heat transfer through the coils. Hard water will leave mineral deposits in the water coils which will insulate them and significantly reduce heat transfer, so you may also need a water softener (and water softener salts undermine the biological action in a residential septic system).
An indirect domestic hot water tank connected to a high-efficiency boiler will provide both central heat and nearly unlimited hot water with very little standby loss (no separate flue), with a burn rate a fraction of a large tankless unit.
Your point is correct that demand water heaters are more of a luxury item than an energy conserving solution. Still, most gas tank style water heaters are about 60% efficient due to the passive loss from the flue pipe. And if you get your electricity from coal, at 30 BTUs per 100 BTUs extracted from the ground, it is practically criminal to use electricity to heat water.
The best way to reduce your energy bills is to send the kids to college. Or get yourself a solar water heater.
Short of that you can also use a demand water heater to heat a tank in a side arm arrangement in the same way that Robert is suggesting that you use a boiler. and as he points out the elimination of the flue in the center of the tank will dramatically improve the stand by heat loss issue.
However there are some demand water heaters that are intolerant of warm water feeding into the heater, the Tagaki you have, Quietside and Rinnai are better than most but when the burners run at a low BTU output due to warm incoming water they can develop a sooty burn and load up the heat exchanger with a layer of soot which is more difficult to remove than lime scale. So using a boiler, if you can afford it, is the better option.
But I'm a cheapskate, so I've been using the Quietside ODW-120A condensing demand water heater in a side arm configuration which is readily available for under $1,200 and vents through standard 3" PVC up to 45' long.
You can see the pipe diagram we're working with here http://chandlerdesignbuild.blogspot.com/2009/11/combining-solar-hw-with-radiant-floor.html Please understand that it's something of a mad scientist experimentation shown here, and while I am a licensed plumber the diagram is certainly a work in progress and you copy at your own risk.
Michael,
You wrote, "The best way to reduce your energy bills is to send the kids to college. Or get yourself a solar water heater."
You're right about the kids, but not about the solar water heater. Plenty of studies have confirmed this; most people won't see a payback for a solar hot water system for 30 to 60 years.
So, here's my version: "The best way to save money on hot water is to use less." This means choosing a front-loading washing machine, installing low-flow shower heads and faucets, and reducing the diameter of hot water lines to distant fixtures.
Martin
What sort of energy cost inflation assumptions are those studies plugging in to prove such a poor payback on solar hot water? I used to buy gas at twenty six cents a gallon, I'm thinking that it will be a lot more than it is today in the very near future.
My goal is to save energy and give people homes that are a joy to live in. Warm floors and endless showers and luxury baths warmed by the heat of the sun at a price that will stay constant and make people feel less stressed about global warming & the cost of energy all make good common sense and business sense to me.
Sorry, this computer is missing a few keys. need a go-back and edit function on this site.
Michael,
I was thinking of a 2006 study by Steven Winter Associates. They looked at two solar hot water systems, one in Massachusetts (installed cost, $7,800) and one in Wisconsin (installed cost, $6,500). The Massachusetts system saved $135 per year, while the Wisconsin system saved $86 per year.
The researchers performed a simple payback calculation; obviously, such a calculation is burdened by all the usual limitations of simple payback calculations, including the fact that it doesn't include an escalation clause for energy prices. The payback period for the Mass. system was 58 years, while the payback period for the Wisconsin system was 76 years.
The Mass. homeowners are getting a 1.7% return on their investment, while the Wisconsin homeowners are getting a 1.3% return on their investment. They would probably prefer to have invested in a certificate of deposit, even if it only yields 2.5%. After all, in 40 years, their solar equipment won't be worth anything -- but they would still have the capital if they bought a CD.
Finally, it should be pointed out that the researchers assumed zero maintenance costs -- and we all know that's not going to happen.
Robert....I do understand my parental responsibility but I just have to pick my battles or I sound crusty old sheriff all day long. I was just trying to say that limiting hot water capacity is a good thing for the planet.
Another mistake I made with the tankless.....trying to use it as a backup for the solar hot water system on the roof. Turns out, the Noritz I purchased was not designed to accept preheated water like you said Michael. And it was not a sealed combustion unit so we ended up cutting a hole in the floor to get combustion air from the crawlspace.....a rather stupid energy penalty which impacts the IAQ of the house. I know, I know.....so many lessons learned.
I am thinking of replacing the Noritz with an indirect water heater, Robert....connecting it to the boiler, then installing an on-demand recirculation pump in the master bath. Any suggestions on the best models?
I just think the green building industry is being directed too heavily by good marketing departments of major manufacturers. People believe green building is expensive because they think it means buying tankless, PV, geothermal, solar hot water, bamboo, etc. I am embarrassed to say that I bought the marketing.
Conrad,
I've used the Triangle Tube Smart tank, which has a very low pressure loss tank-within-a-tank heat transfer system, using high-grade stainless steel (no sacrificial anode required). Because it has 1.5 to 2.5 times the heat transfer surface area of a coil-type exchanger, the recovery time is much quicker, allowing use of a smaller tank with less stand-by loss. Their corrugated and expanding inner (domestic) tank is self-descaling, and they use 2" of urethane insulation for minimal conductive heat loss. I would also recommend their Prestige direct-vent modulating-burn rate boilers.
Thanks Robert. I will look into the Triangle Tube Smart tank. And possibly into the Prestige boiler if I end up replacing the oversized boiler. That is probably doubtful because it is only 6 years old....but it does chap me that it is probably twice as big as necessary! Another issue....
Further comments on reducing our domestic hot water needs...
Our grandparents thought themselves fortunate to have indoor plumbing and bathtubs (which use less water than showers), but now we believe we can't live without at least a couple of shower units (running simultaneously) in a home. Our lifestyles are now so demanding and time-constrained, in order to afford the myriad luxuries we consider necessities, that we can't conceive of taking the time for a luxuriant soak in a tub, let alone a quick sponge bath which requires perhaps a gallon of water.
The best way of all to reduce domestic water consumption is to eliminate indoor plumbing. I can attest to the fact that it's not a necessity for a good life. For many people in the world, in fact, it's an unattainable luxury. 34% of the global population doesn't have indoor plumbing (similar to the US in 1950) and 83% don't have access to safe water.
The typical American consumes 70 gallons of fresh water per day for domestic use, another 200 gallons per day for commercial and public uses, and an astonishing 1200 to 1900 gallons per day for agricultural usage. 20% of the world's population is already experiencing water stress, growing to 30% by 2025 (according to the UN), with water wars expected to be a major threat in this century.
A 20-minute hot shower is not an inalienable right. In fact, it may be a luxury that the earth cannot afford.
If you want them to stop taking long showers, unplug the tankless ;P That will stop it fast. Also consider a Drain Water Heat Recovery system (I like the Powerpipe, but there are other good ones out there), they save more as the shower is longer. Alternatively, you can put a super low flow shower head, showering may become less fun then and hence showers will be shorter, or at least you will save money (or you can use it as a punishment, until behavior improves).
Essentially though, it's a discipline problem, and the above are just passive-aggressive solutions to the problem that your authority must be enforced.
Tell me about these Drain Water Heat Recovery Systems. Don't you need a lot of space (3-5') under the shower to attach these systems....like if the showers happen to be above a basement. Is it possible to attach them horizontally (with a slope) in a joist bay if you are willing to remove and repair drywall?
Yes, install an energy-saving tankless, then patrol your showers daily to limit usage, every parent's dream. Or change the tankless to a highly insulated 30 gallon storage tank instead.
Conrad,
Here are links to two brands of drain-water heat recovery devices:
http://gfxtechnology.com/
http://www.renewability.com/power_pipe/index.html
As far as I know, they have to be installed vertically, not horizontally.
Yes, the PowerPipe does need to be installed vertically so you need access to the drain pipe below. And they costs $6-700, plus installation....might not be a bad idea in the right situation...if you already have a highly efficient WH, well-insulated water lines, and an on-demand recirculation pump
The PowerPipe is less expensive and more effective, since it uses flat heat exchange tubing instead of round and multiple parallel tubes to reduce pressure drop.
But any such system needs to be installed vertically to take advantage of the "falling film" property of water in a large-diameter drainpipe. They don't, however, need to be installe directly under the shower. They can be horizontally offset to another vertical location, as long as the horizontal run is plastic and insulated.
Robert,
Are you saying that using the PowerPipe (I did call them...they told me $6-700 plus installation....does not seem like a small amount?) should be higher priority than a better insulated, more efficient WH (like the Marathon WH), better pipe insulation, and an on-demand recirculation pump? I just think that we need to prioritize our methods by how effective they are and how much they costs.
Conrad
I think most would agree that the top priority is to improve the efficiency of the water heater, followed by the insulation of the pipes and only then to add the drain heat exchanger.
I see the a demand type (Metlund) re-circulating pump as more of a water saving device than an energy saving device. It is certainly a luxury to no longer have to wait for hot water and in some luxury markets it is no longer an option.
My interpretation of Roberts comment that the Power Pipe was more effective and less expensive was that he was comparing it to the GFX heat exchanger, not to other methods of reducing the energy used for heating water.
Thank you, Michael, that's exactly what I was saying (I thought it was obvious). And I agree with your suggested priorities: efficient water heater (and tankless isn't more efficient than a well-insulated indirect tank, if there already exists an efficient boiler), install heat traps on tank if hot pipe extends vertically, insulate hot water pipes.
Recirculation system is necessary only with long runs or poorly insulated piping in unconditioned space. If it's running full-time or by aquastat to maintain pipe temperature, then it will be an energy drain; but if it is on-demand or occupant-sensing, then it will save both water and energy.
Drain-water heat recovery is an expensive option but with reasonable payback for those who take lots of long hot showers.
On new construction or renovation, replacing copper pipes with home-run PEX and keeping plumbing centralized around a wet wall will result in quick hot water response and long-term efficiencies.
Thanks Michael......Robert, I advocate the Metlund on-demand pumps because you can get them for $3-400 and they install very easily (if you have plug under the cabinet)....and you then waste very little water waiting. I think people should just measure the amount of time it takes to get hot water to the sink or shower. It takes 40 seconds to get hot water from my tankless which is less than10 feet away downstairs....Of course, the Noritz has the delay in firing and I don't remember the route to the bathroom but....
Homerun PEX in a manifold (if that is what you are referring to) can be a good option, I suppose, if they are small diameter pipes. But remember, you wait for the hot water at the sink to come from the manifold...then step over to the shower and wait for the hot water to come again from the manifold. Seems to me, a push button recirculation system gets the hot water to the bathroom without wasting anything...hot at the sink and shower.
The minimum flow delay of many tankless water heaters is one of their inefficiencies, and one of many reasons that I advise against them.
One of the many advantages or PEX domestic water piping over copper is that they are highly insulative and generally don't require pipe insulation. How long you have to wait for hot water is largely a function of how compactly the plumbing system was designed. If bathrooms are stacked over the water heater with a single wet wall, there is very little waste of either water or heat.
A demand ciculator is necessary only in poorly-designed homes and what it wastes, is electricity.
Robert,
The on-demand circulator runs only for a short time....push the button once in the master bath...it runs for a short period, providing hot water to all bathroom pipes, if plumbed well. Push it only once in other bathrooms and the kitchen, with well insulated lines, the hot stays present. This probably happens once in the morning and a few times in the evening. Not a big deal from my perspective and will likely be code someday when water conservation becomes critical.
Of course, it becomes more wasteful if you use an occupancy sensor. Then it comes on more often as you (or your dog and cats!) enter and exit bathrooms, laundry room, and kitchen.
Happy to see some common sense on the tankless heater craze. A local paper in its 'going green' column suggested that a) running out the cold water in the pipework to the hot faucet could waste 30 or 40 gallons a time and b) a tankless heater would fix this problem. 30 gallons of run-out would entail around a quarter of a mile of 3/4" pipe. The mind boggles.
"30 gallons of run-out would entail around a quarter of a mile of 3/4" pipe."
Actually, it would require almost half a mile of 1/2" copper pipe to contain 30 gallons of water, and at a flow rate of 3 fps it would take more than 13½ minutes to flush out 30 gallons of water.
Metlund D'mand system has a sensor that if the water in the line is hot it will not start up again if someone punches the button.
Also a quick shower uses far less water than a tub bath.
Robert you're right. I was being generous in allowing 3/4" pipe. Also, with any size of pipe 30 gallons would take 20 minutes to run through a 1.5 gpm low-flow head.
And then with up to half of mile of pipe, water starting hot from the heater would clearly be stone cold by the time it reached the shower, so the wait time would really be infinite ....
Robert you're right. I was being generous in allowing 3/4" pipe. Also, with any size of pipe 30 gallons would take 20 minutes to run through a 1.5 gpm low-flow head.
And then with up to half of mile of pipe, water starting hot from the heater would clearly be stone cold by the time it reached the shower, so the wait time would really be infinite ....
"a quick shower uses far less water than a tub "
"Quick" is the operative word.
A tub with a body in it might hold 35 gallons of water. A 10-minute shower would use less water than that, but the typical 20-minute shower that I believe most Americans take would use more water (at 2 gpm) than a tub. And 100% of the heat in a tub is recyclable if it's allowed to cool to room temperature before draining (which I always did in the winter when I had indoor plumbing).
20 minute showers? Who has the time? OK, maybe your kids, if you let 'em. I don't know what I'd even do for ten minutes in the shower. Two, three minutes is plenty.
2-3 minute shower? What's the point. Americans are obsessive-compulsive about body cleanliness and consequently more prone to disease (letting children, for instance, play in the dirt gives them immunity to many common pathogens).
Your daily 2-3 minute showers use more water than a weekly bath, which can be savored for an hour (returning its heat to the house), offering not only body cleansing but psycho-spiritual cleansing.
Robert-
Your desire to save the planet by eliminating bathing is moronic. Please, just shut up.
If mis-representing another's statements and making sweeping judgements about another's reasoned arguments is "common sense", then I'll gladly stick with "moronic".
Excessive bathing is detrimental both to bodily health and to the health of the environment. That should be common sense, but alas there is precious little of that quality left in "civilized" humanity.
Making your lack of personal hygene a cause is idiotic. Nothing quite like a sweeping judgement than "Excessive bathing is detrimental both to bodily health and to the health of the environment."
Guys, lets not go down this road.
Robert contributes a lot to this site. He is passionate, well informed, more than a little eccentric and sometimes a little self-righteous, but he really does add to the discourse that makes this site a good resource for all of us. I often disagree with him but I really value his perspective, and I'm a little eccentric in my own way and I appreciate you all not calling me moronic, though I'm sure Martin and Robert have both had to bite their tongues a time or two.
Calling him moronic is equally self-righteous and unproductive (as is hiding behind a pseudonym). Lets please be civilized here, use our real names, and work together to elevate the discussion to our mutual education and benefit.
If "Common Sense" means using invectives such as "idiotic", "moronic", "just shut up", à la Rush Limbaugh and Bill O-Reilly, in place of honest, rational argument, then perhaps it's a good thing that there is so little of it left in our culture.
Perhaps you would be willing to identify yourself rather than hide behind the anonymity of a Nom de Plume that you clearly do not deserve. In any case, such low-brow responses have no place on a "green" discussion forum. You might consider a regime of mental hygiene.
Thanks, Michael. If I had seen your response before posting my last, I would have let the matter lie.
Yes, I stand with Michael....let's keep it respectful. We use the forum to learn, not to judge others. It is OK to say..."I disagree with you", etc but not OK to abuse people. I too appreciate Robert's involvement even if I disagree with him. Speaking of which, Michael, Robert, do you care to comment on my entry in the Blog section. I need to find the best solutions to making my house more energy efficient.
Since one of the issues here is the length of time in the shower... perhaps a shower timer would help with that. There seem to be a few of them on the market. I haven't personally tested them, but they seem like a good idea. One of them has a 5-minute reset period where the shower can't be turned on full blast for that time period.... I know that would discourage me from lollygagging in the shower.
Children need to learn economics and responsibility; set rules--no 30 min showers; running out of hot water shouldn't be the limiter. If we don't teach them, who will? Our large capacity good quality tankless didn't cost 3-4 times more than a storage tank water heater--$600, and located close to point of use we don't need a recirculator. Of course, if reality is all worst case scenarios, then one has to deal with them. We love ours.
One thing not mentioned in this discussion is that a tankless HWH is a great solution for some, not all. If you have a big family in a 3 bath house and showers, laundry and dishwashing is going on all the time, the savings are not worth the minor inconveniences. But I live alone and travel often.
I use cold water for laundry and quick hand washing. My only hot water use is showers, dishwashing and washing up. No point in keeping 40+ gallons hot 24/7 because I MIGHT use it 2-3 time a day. And when I walk out the door, I might be gone for 12 hours, 24 hours or a week!
I never said that it was better to have a cheap storage tank water heater. No doubt, those waste energy in standby losses. But, the better, highly insulated storage tanks don't lose much in standby losses.
Tankless, I think, can be fine if you can find dependable, affordable units....and if you can limit the hot water usage by shower timers or push buttons...or if you have a big family. But I do stand by my original statement that tankless hot heaters are more of luxury item as opposed to a green product. I doubt that any any energy has been saved from the good marketing of these products.
Food for thought:
I was visiting my brother in Seoul, S. Korea a while back. His whole appartment (all 600 sq ft which was considered an enviable size) was serviced by a tankless hot water heater. When you needed hot water you had to press a button on a control panel and it would activate the tankless heater. The heater then was able to supply hot water for a period of about 10 minutes, then you had to press the button again if you wanted more hot water. The big catch was that you could only press the button five times in a 24-hour period. This wasn't just for showering but for all hot water needs.
This set-up may not have been typical of every home in Korea, but it does show that concepts of hot water use vary widely even within the developed world. In other words there are many, many people living in civilized parts of the world that do just fine on what some North Americans might consider a water ration.
In fact, the early Christian settlers of N. America thought it was a sin to bathe. Ben Franklin imported the first bath to the "new world" and no house in the thriving city of Quincy MA ("city of presidents" "birthplace of the American dream") had an indoor bathroom before 1820. These were people who considered themselves highly civilized.
Through the nineteenth and early twentieth centuries, a weekly bath was the norm. It still works for me (I have to fire up my wood-heated hot tub in order to bathe).
One of the best energy saving devices I have ever used cost me about $8.00---a 3/4 inch ball valve installed on the hot (exit) side of the water heater. My teenage sons quickly learned to limit shower times to under 5 minutes after instantaneously having their hot water eliminated. Cold water seems to awaken the senses and get one to think "green".
And by the way I had a 50 gallon tank type electric water heater (new price maybe $300); installed in the utility room; within the conditioned space; in a heating climate; centrally located; common wall to the kitchen; directly below two bathrooms above; next to the washing machine; with no hot water supply line over twelve feet from the heater; with all hot lines insulated up to the valve, faucet, or stop; and a quick action ball valve. Built the house in 1989, the new owner (5 years) still is using the same water heater. The unit gets flushed every couple of years. I raised three kids into their late teens. How can one justify spending upwards of $3,000 on a 'green' tankless water heater?
tankless... I agree with the original posting... nothing is green if it is expensive to start with. That said... the one post that said they work for low use.. like a weekend cabin... etc... maybe... We now install switches upstairs for electric tanks... for weekend camps.
Solar... solar needs to get down to $1000. It can. Then... it makes sense.
Same with GEO heating. Install cost is too high. We need to do the ground work for less. Better in my mind to superinsulate and passive/active heat... depends on location of course... but insulation/thermal mass work where needed... or... move to Hawaii... open windows here we come.
Chandlers system looks interesting.
aj
Hi aj,
I don't think you'll ever see the cost of the ground work for geothermal coming down, more than likely it'll get more expensive. Well drilling or excavations require expensive equipment with high(er) paid larbor to operate. And there's no saying where fuel, insurance, material, etc. prices are heading.
Cars were expensive to Ford came up with his assembly line. IE... say a driller drilled a thousand holes in a subdivision... I would think the cost could be dropped in half for the enitre install.
Superinsulated 1 tone systems for $10,000 complete. I bet it's doable. Where is our mondern Ford?
A smart kid in China is solving all of this most likely as we post tonight.
aj
begging for edit to be added!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
If a developer incorporated geothermal into a project design, then yes, it would be much cheaper because a large chunk of the price for drilling is mobilization.
I've been going out to Star Island, in the Isles of Shoals, off the coast of NH, for a week in the summer, for many years. They have to conserve their fresh water (toilets are flushed w. salt water; they now have I think the only seasonal small sewage treatment plant in the country) and so showers have always been restricted to twice a week, though now it's getting distributed over more days for shorter periods of time. Shower heads are all equipped with a little button. You hold the button in, water comes out. You let go of the button, water stops coming out. You get wet, you use both hands to soap up, you rinse. It's not rocket science, and it's certainly not at all expensive. You get used to whatever you have to get used to; it is true that our nation has something of a hygiene & anti-germ fetish, which doesn't help the environment in any way, and actually seems to make everyone sicker.
I'm grateful to you all for this useful discussion. I'm finding that going "green" can be a profound moral process, because in some cases you have to turn away from the siren call of luxury and personal convenience, seductively advertised all over the place, and toward something less "convenient," in the service of a principle that is probably rather abstract to a lot of people.
For another non-water example, I'm currently working to shift my paradigm away from a gas stove, with which I'm comfortable, toward an induction cooktop, with which I have no experience, because it seems to be a greener way to cook food. The economics of the decision being equal, it's a hard process, and I wonder how others, much less fanatic than I, will be persuaded to do something similar.. The discussion up to this point certainly illustrates that the calculus of "most green method" is a far more complex one than I realized when I first started working to bring my habits more in line with planet health.
Yes, Lydia, the calculus of living lightly and rightly is not a simple one.
But unless you're producing your own electricity, an electric stove of any kind (microwaves included) is perhaps the least green way to cook, not to mention possibly the least healthy.
Electricity generation is a highly inefficient method of converting concentrated energy fuels into usable power at long distances. Most combustion-powered electrical generators are no more than 30% efficient, and much less when distribution losses are considered.
The ancient wisdom tells us that cooking with the "cold" heat of electro-magnetic fields takes the chi (life force) out of food, while cooking on a flame adds energy.
Martin,
I've read through the SWA solar study (www.swinter.com/news/documents/CostDesignPerfSolarHW.pdf), and a problem with the authors' conclusions about economic payback is that both systems studied had (acknowledged) significant energy wastage problems with their design. One system had a pumped hot water recirc system (aka hot water down the drain), the other had the solar tank boosting a tankless heater through an incorrectly configured tempering valve (though one questions whether such an arrangement -- solar boosting tankless -- is the right solution in the first place). Personal experience plus that of many others in the local area is that solar thermal in general has a much shorter payback period than the authors suggest.
My family of 4 is located in non-sunny Vancouver Canada, and had an 80 gallon solar storage tank installed mid-2009. The tank is an indirect fired, stratified design, with heat supplied by a natural gas-burning Viessmann Vitodens 100 (AFUE 97%) which supplies heat to both the DHW tank and hydronic baseboards around a mid-1980s moderately-insulated and leaky 2500 sq ft detached house. The solar thermal system is water drainback, with 32x8 worth of flat panels on a WSW-facing roof. Total installed cost after rebates was around $9-10k, with a chunk of that going to the roofer due to extra installation difficulties to do with an in-roof design for the panels on a concrete tile roof.
My savings on record due to the changes in the heating system, even given that BC has among the lowest energy rates in North America, and with fairly little in the way of changes to behaviour, has been about $900 - $1000 per year. Depending on how one dices the numbers up (eg, by looking at summer gas consumption records as a guide to DHW usage) a reasonable estimate for simple payback on the solar thermal system is on the order of 15-20 years. Even if one rolls in the new combi-boiler (approx. $12-14k Cdn installed, including some flue work to do direct venting), which in this system behaves similarly to a well-buffered tankless, one still ends up with 24 years for the whole enterprise. This is a factor of 2 to 3 faster than the SWA study cited. And, that's before the ongoing programme of family behaviour modification I've started (heh) and further tweaks of the heating system (eg, timing on DHW supplementary heating, opening up chases to retrofit additional insulation on hydronic pipes, etc).
Looking at the experience of others (eg, http://www.bcsea.org), one sees even faster payback, more on the order of 8-10 years. The 60 year payback from the SWA study is more commensurate with solar PV payback in this part of the world (ie, without all the PV rebates in the US, the high FIT in Ontario, and the cheap 6.2 cent/kWh hydro electricity here in BC).
The drainback system I chose was based on some research suggesting that water-based thermal systems have a significantly longer lifetime (~30 years) as compared with systems based on more corrosive antifreeze (~10 years), which also require annual drainage. We'll see in a few more years (or decades) whether this continues to hold true.
Granted, Vancouver has relatively mild winters, but I have read reports of water-based drainback working in even colder climates. And, contrary to Olympic media coverage, we do get snow here on occasion.
Regardless, if solar thermal can pay back in grey Vancouver, it ought to be able to pay back in other places (and not just sunny Florida).