Cost is not a metric in efficiency, efficiency is the metric.
With alternatives you pay for capacity never by-the-watt or by-the-therm, therein lies a pack of lies because costs can be manipulated easily as seen by how reliable, honest, forthcoming, transparent, and socially concerned the power companies are about their profits. Grid-tied is no fun, try off-grid and you'll never go back and would definitely install solar hot-water if feasible not every lot is.
A heater can cost $5k-6k no problem and how many therms do they produce without power or fuel?
So, there you go, you pay the same for capital depreciated and add in by-the-watt fuel and that's supposed to be cheaper, it can't be more efficient and certainly isn't sustainable with steam plants, until they go it's all downhill.
I simply can't buy alternatives being more expensive over the life of the system, sorry, the math does not work but see many reasons why.
Most hot-water are DIY shallow roof add-ons that cost $500 for the deluxe version that passes code but the system needs a fluid heat-exchanger in the hot water tank with about 150-gal capacity to have enough thermal-mass to make withdrawals less enough in proportion to reduce input needs to get to a temp, 80-gal is too small by far to do this for off-grid in general.
Thermally it's impossible without thermal-mass for storage in a home or any building trying to keep the interior in a comfort zone with the same heat-loss rates to be more efficient without it, whatever the heat source.
Solar hot-water uses that same principle in a properly sized system to do the same thing as PV-battery w/o converting the energy to another form, it therefore is the most efficient use of heat so physically impossible for it to cost more by value returned per investment dollar without the slick tricks on the bills.
This is hot-water not electricity, it's pipes and a tank and a shallow pan on the roof, not real space age stuff. For passing code reference EarthshipBiotecture.org and utube for videos on constructing them contractor or homeowner.
In 2009 (Seattle area) when I looked at and added solar hot water to my house, I calculated the payback vs a tankless... and the solar hot water heater would take about 40 years. If the alternative is heating with electric resistance heater only, it would have been perhaps ten years. But now compared with solarPV and heat pump hotwater heaters, Straight solar thermal - is very dependent on location.
Code requirements are also dependent on region, with snow loads, wind loads being important considerations - often items ignored by the DIY.
The collectors ate the lowest cost portion of the system.
The number of solar thermal installations across the US have been dropping from good reasons... and they've dropped in Europe as well. The price of solar PV had dropped far enough to significantly alter the economics. The price of solar hot water has thus far remained the same or climbed somewhat higher.
When you factor in the alternatives, solar PV with HPHW or resistance, or NG. the ROI for solar thermal doesn't work except nationwide... but it does still work in very specific areas. Hawaii and regions where NG and electric rates are high.
No slick trick of the bills -- been there done it...
Thanks everyone I have some work to do. Dennis has given some good pointers. And Anthony I will also go to dealer and try get references as well.
I had an early Bosch Aquastar - I hated that thing and still curse at the memories of it today. Horrible technology.
I now have the Rheem Prestige whole house 199K unit. I love it! I have had it in for about 2 years and have had no problems. My demands on the unit are limited since I only have 1.5 baths. My incoming water temp from the street can be very cold since I live in Minnesota. It has no problem making all the hot water I can use. My unit is natural gas.
I have seen very little savings going between two tankless units but when I switched from a 40 gallon tank to the Bosch unit I think I got about a 30-40% savings on water heating. Overall, water heating is not a huge portion of my bill but it was noticeable.
Trading a .67EF water heater for a .82EF? 15% savings on water heating costs for an extra $1,000 or so installed cost? You have to use a LOT of hot water before saving enough in NG costs to pay for itself. Saving the space can be a good reason to switch, especially if it's conditioned space.
I'm seeing $200-$300 annual hot water costs. That's what, $25 a month for hot water? Even if tankless cut that in half (which is VERY unlikely) the savings starts getting so small you'd need a magnifying glass to "see" it. If you are doing tankless for energy savings, think again. That money can be put to MUCH more effective use elsewhere.
I really like the Navien - they have fantastic features. The built in buffer tank and pump alone are justification to use it and no other.
If you don't have a good "reason" for tankless, put in an electric or heat pump water heater. I really like electric for their simplicity and low cost - it leaves a lot of money in people's improvement budgets for items that really save energy and improve comfort.
Switching from gas to electric makes no sense unless it's part of a larger plan to go to an all electric home. Electric water heaters cost 3X as much to operate vs gas in most parts of the country. If you are going to pay the monthly gas meter fee might as well get as much use out of it as possible.
Bob, sometimes your critical thinking and math seems simplistic and leans toward dogmatic regurgitation of performance myths. You realize that quite possibly these myths are created and perpetuated by special interests? That you're disseminating bad advice makes you unwitting tool for others gain?
Perpetuating the myth that NG is cheaper by 3x is false and harmful to all interests but equipment manufacturers, pipe fitters, and the NG industry.
I don't think you work for a gas company, but unless you can support your assertions with math I'm going to continue to defend the position that electric water heaters are a much better choice than gas.
I have more than armchair experience with energy consumption. I've actually gone to other peoples houses and done this work. If electric hot water is so expensive you should be able to immediately tell from energy history whether the home has gas or electric hot water. I am unable to and I've been to 100's of homes and seen 100's of bills. I challenge you to spot the electric water heater.
I has been my experience that electric water heater system efficiency, not myopic combustion efficiency but total cost, is so close to natural gas that it is hard to differentiate. The opportunity for meaningful savings is a perfect example of excluded middle fallacy. It isn't completely non-existent, but it's as common as the guy who drives his car 60,000 miles a year. It's a rare bird not a pidgeon.
Harmful how? Combustion appliances kill 1000's of people a year. They are a time consuming impediment to Energy Efficiency improvements. Enclosure improvements by people who don't understand this put millions at risk. Ask yourself, do you want to perpetuate thinking that can be significantly harmful to people? Why would you?
You think the case for electric water heaters is narrow and gas water heater are panacea of savings - support your assertions.
A DTH of NG is an average of $10 on a national basis. 1KWH of electricity averages about 12 cents. There are 293KWH in a DTH. 293 x 12 cents = $35.16 for the same energy that NG provides for $10.
Would you pull a NG furnace and replace it with straight resistance heat? Same concept. Same combustion risks, same efficiency issues.