Condensing Tank Water Heaters

Dave AngeliniDave Angelini Solar Expert Posts: 5,501 ✭✭✭✭✭
Still pretty expensive but if you have a need for a back-up heat source for radiant or space heating these new tank heaters are hard to beat. 4 gallons a minute from a 1/2" gas line and 96% efficient. They have the space heating lines plumbed and should be much better than a tankless over time with hard water.

With several collectors and a 100 watt PV panel for pumps the heater will consume zero energy because it is pilotless.

http://www.hotwater.com/lit/spec/res_gas/AOSRG45101.pdf
"we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
 http://members.sti.net/offgridsolar/
E-mail [email protected]

Comments

  • BB.BB. Super Moderators, Administrators Posts: 31,068 admin
    Re: Condensing Tank Water Heaters

    That AO Smith 96% efficient water heater--Whenever I look at Tankless water heaters, I keep coming back to that tanked water heater as my choice too...

    For some reason though, they are only listed as a 6 year warranty... Add the $1,600-$2,300 price (quick web search) vs $500 or so for the local 12 year warranty standard gas water heater equivalent... And assume that I save 50% on my gas costs (instead of the 20% that tankless water heaters really save on "typical" gas bills)...

    $20 per month * 50% = $10 per month savings

    $2,000 - $500 = $1,500 cost differential (not including labor for direct venting)

    That is 150 month payback or 12+ years... But I may have to purchase 2x the 6 year super efficient heater vs the 12 year cheapie... And it is much worse if I don't save 50% on my bill...

    It may make sense as the "storage tank" of a solar thermal system if I will last longer than 6 years (as this heater is only 50 gallons I may still need a second storage tank to get 80+ gallons of storage for my demands based on the usual rules of thumb).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Condensing Tank Water Heaters

    As far as net/net energy consumption, it becomes a complicated equation, demand vs condensing gas. I confess I have done ZERO research on the subject. So while a condensing unit should heat X quantity of water X degrees using less gas than a good demand, the question is which delivers most efficiently at the tap?

    For example, standby losses, while slight with a tanked water heater, (especially if the "lost heat" is lost to heated space 365) but that loss is real. My intuition is that a tankless would win with smaller sporadic use, the tank type with larger draws, more regularly.

    Factor in the price difference between a good demand unit ~$500-800 and the condensing unit ~$16-2300 and I think over the life of the unit, the demand is PROBABLY cheaper net/net.

    I also would think that for pre-heated water the demand would be better. (Just an opinion however!)

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 31,068 admin
    Re: Condensing Tank Water Heaters

    Interestingly, from the research I have done to look for the "optimum" deal...

    Regular old tanked water heaters and standard tankless water heaters are both 80% efficient at heating the water.

    Where they differ is the standing hot water heat loss of a tanked heater (plus pilot light) vs the no standing hot water/pilot of a tankless water heater.

    The condensing hot water heater resolves many of the tanked issues of standing hot water heat loss through insulation and a powered vent that does not allow warm air to go out your vent--plus the more efficient heat recovery (stack air is cold enough for PVC (plastic) piping) and to condense the water out of the combustion gasses...

    So, for high flow/lots of use (i.e., restaurant/commercial), it appears that the condensing hot water heater can be more efficient vs a tankless unit (assuming that the heater is 96% efficient at making hot water hot vs 80% for a tankless heater).

    For those of use with natural gas -- this condensing heater seems to be an ideal way to bring solar thermal (or desuperheater A/C based) into a home (other than the costs).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Condensing Tank Water Heaters

    Bill,

    Clearly you have done some research, and as I said, I have not. In fact I know less than nothing about condensing water heaters, and a bunch about tankless ones. My thoughts are just that, thoughts and intuition.

    I do know that the Takagis can be had with a back draft stack damper to keep cold air from passing through the heater when idle. Interestingly enough, I have installed an automatic stack damper on my standing pilot Paloma. This is a thermally activated damper that apparently is out of production and has been recalled. I think the problem with them is that they don't failsafe open so that in the event of failure, you run the serious risk of CO entering the house. I personally choose to take the risk for two reasons. First, we only run the hot water for short bursts, and it is right next to the shower and the kitchen. I can visually look up the draft hood to make sure it it opening properly. (It is built with bi-metal vanes that open as they are heated,, pretty cool actually!). The principal reason for the damper is to prevent very cold air from migrating down on a winter night, potentially freezing the water course. The tall "B" bent stack can get quite cold. The standing pilot is often not enough to counter act the -40 outside air trying to settle in the pipe. (Remember, these are draft hood units, so it is possible that the pilot contributes little to a draft when it is very cold). This has the added benefit of stopping a considerable out flow of heated air leaving the building 24/7.

    I know that my sister in law has a condensing boiler/water heater combination and it is very efficient, and vents through a 3" PVC pipe. It is interesting to me that the demand water heater folks haven't figured out how to make them more efficient, and how to lower the stack temperatures so that you wouldn't need to vent through expensive stainless vent systems.

    Tony
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,501 ✭✭✭✭✭
    Re: Condensing Tank Water Heaters

    Yes the loss thru the flue, the high recovery and low maintenance are the reasons to use a condensing. Since all my applications are for offgrid and used as a back-up to solar hot water I have very different metrics and cost are reaonable compared to other solar water back-up options.

    They are still pretty new but they do get rid of the old idea only using an electric for back-up because of flue loss for solar domestic hot water. With the 4 gallon recovery rate they also will work for space heating as long as the application is a reasonable size.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Condensing Tank Water Heaters

    Dave, New? the brand maybe....

    I just had my Lennox CompleteHeat 10 gal tank version ripped out:cry: in January, last, after 12 years of frustration over a very poor design flaw that the "P. Engineers" designed into the unit... Product now discontiued as there is a class action suit in play south of the 49 th parallel.

    Problem was a TACO circ pump was installed on the top of the tank and Taco specifically says not to do that on the replacement part packaging... steam would be generated and the plasic seals would 'melt'

    See Bob Villas BB for a litany of details on CompleteHeat problems

    I am also aware that there is also Polaris model too, with similar issues..

    Replaced Lennox with a Navien tankless modulating condensing type,:D and the gas savings are substantial so far. the Lennox was 96% rated at time of installation, but degraded over time.. The new unit provides both DHW and heat for the house.

    I have HARD water with 65 grains of hardness plus 5 grains of Iron, you can sandblast the dirt off in the shower if the softener isn't working... and you come out dry and crusty...

    As there is no place for the scale to collect now, I am watching for signs of unusual functioning of the unit... so far so good.

    word of caution, you want to be sure to flush the tank of any scale buildup every 6 months or the tank efficiency drops...

    HTH
    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,501 ✭✭✭✭✭
    Re: Condensing Tank Water Heaters

    One of the really decadent things about solar hot water is you can flush the tank monthly and there is no energy loss. Also the really good thing about a rainwater source is the zinc rod lasts forever.

    The AO smith tank I am going to use for a customer won't be installed until 2010 during summer. I hope there are more choices by then specifically how much energy the fan/igniter needs and the big killer standby power loss.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • System2System2 Posts: 6,290 admin
    Re: Condensing Tank Water Heaters

    I am confused. AO SMith told me I could not use the Vertex condensing model since the controls would reset when my inverter went to sleep each night. I really would like to use this heater , but do not know how to make it work with the off grid setup that we have. (battery backup on offf grid pv array).
  • audredgeraudredger Solar Expert Posts: 272 ✭✭
    Re: Condensing Tank Water Heaters
    I am confused. AO SMith told me I could not use the Vertex condensing model since the controls would reset when my inverter went to sleep each night. I really would like to use this heater , but do not know how to make it work with the off grid setup that we have. (battery backup on offf grid pv array).
    What with refers, freezers, heat circulating pumps, tank less water heater, etc. my inverter never sleeps. There is at least 6 watt draw all the time. Plus its turned to ON rather than SEARCH... AO Smith may have misled you.?
  • solarvicsolarvic Solar Expert Posts: 1,053 ✭✭✭✭
    Re: Condensing Tank Water Heaters
    Still pretty expensive but if you have a need for a back-up heat source for radiant or space heating these new tank heaters are hard to beat. 4 gallons a minute from a 1/2" gas line and 96% efficient. They have the space heating lines plumbed and should be much better than a tankless over time with hard water.

    With several collectors and a 100 watt PV panel for pumps the heater will consume zero energy because it is pilotless.

    http://www.hotwater.com/lit/spec/res_gas/AOSRG45101.pdf

    Are these waterheaters covered under the stimulous plan. I was going to do an on demand waterheater but not too crazy about putting another hot exhaust pipe thru my ceiling and roof. I just cut a hole in my ceiling for an attic venelating fan and found that the fiberglass insulation is r-30 and about a foot thick. What lights the waterheater, hope it isn,t a glow bar as they are real energy hogs.
    S:Dlarvic
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Re: Condensing Tank Water Heaters

    just came across this on the Bosch site

    ProTankless GWH 425 HN

    Patented Bosch Hydro-Generated Ignition Technology The Bosch engineers have proven that water can indeed make fire. The pilot is ignited by a super-concentrated spark generated by a micro-turbine. The micro-turbine is activated by a request for hot water in the house. This energy efficient technology makes the 425 HN ideal for households looking to maximize energy savings.* No Electricity Required

    don't know if it will meet all your needs...

    HTH
    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Condensing Tank Water Heaters
    westbranch wrote: »
    just came across this on the Bosch site

    ProTankless GWH 425 HN

    Patented Bosch Hydro-Generated Ignition Technology The Bosch engineers have proven that water can indeed make fire. The pilot is ignited by a super-concentrated spark generated by a micro-turbine. The micro-turbine is activated by a request for hot water in the house. This energy efficient technology makes the 425 HN ideal for households looking to maximize energy savings.* No Electricity Required

    don't know if it will meet all your needs...

    HTH
    Eric

    This is basically the same unit I have at the cabin. It's been working flawlessly for five years now.
  • Dave AngeliniDave Angelini Solar Expert Posts: 5,501 ✭✭✭✭✭
    Re: Condensing Tank Water Heaters

    When I started this thread it was aimed at someone who might want to use radiant and potable heated water by solar with a gas back-up. Since you have to have a tank to use solar hot water the Vortex and similar condensers fit the bill.

    The advantage is they can heat water quickly like a tankless and are more efficient. Radiant is a huge load and running a shower at the same time as the radiant often causes problems with tankless heaters. There just is not enough storage in the piping of the house.

    Down side is the unit needs a small AC power source to ignite and some small standby loss. Small cabin systems are out! A normal sized system would not have a problem but it is a loss that is there. If someone really wants radiant and all the obviously wonderful attributes of heating this way, they will pay the price!

    I have heard of more than a few complaints with getting a tankless to work as well as a tanked heater. Some of the new tankless heaters have a small tank built in which tells me manufacturers are refining the design also. Hard water users are being warned about maintenance in the heat exchangers of the tankless so be aware!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Condensing Tank Water Heaters

    "I have heard of more than a few complaints with getting a tankless to work as well as a tanked heater. Some of the new tankless heaters have a small tank built in which tells me manufacturers are refining the design also. Hard water users are being warned about maintenance in the heat exchangers of the tankless so be aware!"

    I have heard, and had some of the same complaints as well. The biggest is the lag time between firing. For example, when I do dishes, I run the water on for a few seconds, then off. This of course cuts down on the water use considerably, but it also can (and does) leave cold spots in the between time, as the heater takes a few seconds to fire each time. This adds up to some extra water use and on balance, I am not sure which is better. What I have figured out however, is approximately how long I can run the water before it turns cold (between cycles) So what I do is try to run the last of the water slowly so as to not re fire the heater, but to use up all the heated water. In my case it is pretty easy since the water heater is within earshot of the sink.

    Drives Susan crazy, as the net result is probably about 1/4 gallon of propane per year saved!
  • Ralph DayRalph Day Solar Expert Posts: 927 ✭✭✭✭
    Re: Condensing Tank Water Heaters

    Ah Tony, remember the Volkwagen commercial where the incredibly rich man leaves his billions to his quirky nephew who drove a beetle...he said a penny saved is a penny earned...and look what it got him!!:D

    That 1/4 gallon could be the last of a tank that heats the last cup of tea before ice out in another year:p

    Ralph
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