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Solar DHW Tank Lifespan

Steve Fontas
Steve Fontas Member Posts: 26
Greetings folks, I have looked through the threads and can't seem to find the question raised (unless it got buried deep in another thread's responses).

We are in NYC where the water has an average pH of 7.2, average life expectancy of a conventional gas fired HW heater is 10 years. What I am trying to gauge is what kind of life expectancy is there for solar DHW tanks. I realize materials vary so perhaps those of you with experience might be able to offer an idea on a range of manufacturers products? I would imagine that without l the stress of thermal expansion and cooling from the flame in a conventional HWH a solar tank would last much longer.

Let's say for this discussion we are using a 60 gal pressurized tank. Residential usage.


<a href="http://www.nycsolar.org/">www.nycsolar.org</a>


  • hot_rod
    hot_rod Member Posts: 19,289
    I would agree

    that a solar tank, burnerless of course, does not see the thermal stress of a fired tank.

    As the tanks get sediment inside, they do not transfer the heat from the burner to the water, so you have both fire side and waterside issues.

    The amount of water, hardness, TDS are some of other factors that contribute to the life expectancy.

    If it is a steel/ glass lined tank, the anode rod maintenance is part of life expectancy.

    Some solar tanks, like Caleffi :) have dual anode rods as standard.

    Fired tanks have a flue hole through them so there are more welds to fail.

    In some areas glass lined tanks last longer than stainless, and vice versa. Local history would help determine which have the best track record in your area.

    If you plan on using the solar tank as a pre-heat to a second fired heater the first tank will lessen, sometimes eliminate the firing of the second tank, extending it's service life.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Steve Fontas
    Steve Fontas Member Posts: 26
    Thanks Rod

    Funny you should talk about the second tank as I was just reading the single vs. double tank debate on the forum. In general although I believe in the double tank system there are two mitigating factors here in NYC. One is space (our residential boiler rooms are usually not that large, the second is cost. Extra equipment plus labor to install and pip drives up cost to the point where a difficult sale becomes no sale at all.

    BTW I had tried to get a hold of you via e-mail a while back, I think you might have missed my message though. If you get a sec can you reach out to me? [email protected]. Thanks!
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Siggy's Tank

    John Siegenthaler's unlined steel solar tank is almost 30 years old.

    Best of all worlds:  closed system, low pressure ,  drainback.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Steve Fontas
    Steve Fontas Member Posts: 26
    Well I'll tell you what

    Thanks Kevin for mentioning Siggy's tank because it got me spending my whole day reading his articles and such instead of tending to business. Oh well, my customers will be better served in the long run.

    Anyhow, I did find his tank described here:


    I have to say I was skeptIcal when you mentioned the stats. Siggy's tank is galvanized (albeit cold galv.) on the inside. I suppose if that can keep a tank for 30 years then today's coatings would as well, especially the stainless tanks.

    Thanks for the fun reading..
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Best System for Long life for solar DHW tanks

    Lo and behold, 30 years later there is finally a company mass-producing tanks like Siggy's.   Note that the tank wall only sees the deoxygenated water of a closed hydronic system.  The open system Domestic Hot water goes through the huge copper heat exchanger in one pass.   That heat exchanger is just copper pipe, so it should have a 40-100 year life.

    Nevertheless, it's glass-lined for extra life, and pressurizable to 100 psi if you want.    As in Siggy's system, the air in the top of the tank accepts the expansion of the fluid.

    Steve, it addresses your other issues as well:

    1.   You can add an electric element to the top for use as a one-tank system.

    2.   Fewest components of any system design resulting in low cost.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Solar Heat Exchange Manufacturing

    Sorry, here's that  link to the tank:


    Also Pex can be used in the collector loop if you keep it far enough away from the flat plate collector.
    Superinsulated Passive solar house, Buderus in floor backup heat by Mark Eatherton, 3KW grid-tied PV system, various solar thermal experiments
  • Tom in Maine
    Tom in Maine Member Posts: 21

    We have been building unpressurized tanks for about 30 years. I just took one out of service (I wanted to check out the liner) after 24 years of service. It was fine and would have gone on for another long period of time.

    An unpressurized tank has some merits that pressure DHW tanks do not have.

    The big one is being able to rebuild it if it was every necessary.

    The other one is cost and ease of installation. Our 200g tank is the same cost as most 100g pressure tanks with heat exchangers.

    Sorry for the commercial, but I couldn't resist.

    Merry Christmas.

    A lot of tanks,


    Tom Gocze
  • My Solar Tank

    A rubber lined box has to be the cheapest, longest lasting tank around. I talked to a solar guy from California who said he has seen many from the seventies, still in service. I built my 1500 gallon tank for less than a small dual coil tank. It will also allow you to put in LARGE heat exchangers so you can make hay when the sun is shining.

    Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • N2HOTH2O
    N2HOTH2O Member Posts: 2
    Solar Storage Tank Lifespan

    Speaking from only a warranty standpoint. The majority of the glass lined solar DWH Tanks have a mfr. warranty of 6 years. This includes both the internal heat exchanger models and the external wrap around heat exchanger models. There are many tanks that are still in service from the last solar boom about 25 years ago. That being said. The Rheem Marathon Solar Storage tank carries a lifetime tank warranty for the original owner. No anode rods no internal welds to rust out. Rheem makes this tank for solar as well as geothermal/ground source heat pump applications.
  • Steve Fontas
    Steve Fontas Member Posts: 26
    Good looking tanks

    Thanks for the great feedback so far. Bob, a 1500 gal tank in New York City is called a swimming pool, that's bigger than most apartments!

    Happy New Year, gents...
  • Swimming Pool

    Steve, actually it's only 8' X 8' X 4' high. This helps me get 100% of my domestic hot water and I don't need a heat dump, even though I have a LOT of collection surface.

    Thanks, Bob Gagnon
    To learn more about this professional, click here to visit their ad in Find A Contractor.
  • Steve Fontas
    Steve Fontas Member Posts: 26
    Like I said

    Ummm Yeah Bob, like I said. Bigger than most NYC apartments!

    Happy New Year!!!!
This discussion has been closed.