"Traditional" BW, or "Condensing" BW, or "Condensing" American?

Discussion in 'Water Heater Forum, Tanks' started by rickst29, Oct 26, 2009.

  1. rickst29

    rickst29 New Member

    Messages:
    9
    I'll be needing a new natural gas water heater, due to installation of an 85 gallon whirlpool/spa bathtub. I'd love to hear your opinions about four alternative models which I'm looking at. There are two "special factors" at my location, which might effect your recommendations:

    1) altitude 5200 ft.
    2) incredibly "gentle" water.
    3) earthquake zone.

    How gentle? The current WH is 21 years old, and the original anode still has plenty of metal left to sacrifice. No leakage or obvious problems, but the 40 BTUH burner and 50 gallon tank can't come even remotely close to filling the tub. In reality, I know that the efficiency and performance are also far below the even the inadequate labeled capabilities from 1987 (there's both age AND altitude factors). I've zeroed in on two "normal" choices and two of the brand new condensing models. The water is from Lake Tahoe, down the Truckee river into Reno, Nevada -- so I don't have to meet California requirements, but I'd prefer to do the environmental "right thing" if it cost over ten years likes appears to be only a little bit more. Here's my picks-- and please feel free to suggest something else, too, if there's another quality choice which I've left out:

    Cheapest "Normal": BW "Through the Wall" powered exhaust with 2" foam insulation, BW model M-2-TW-75T6BN. But the air near the floor of my garage gets dirty when the wind blows, and through the Donner Pass/Truckee River valley the wind blows very hard very often. I can smell at least some level of blow-back from the current heater, but maybe it's all from the open vertical exhaust flue, with none happening at the burner intake. But I'm in love with our condensing furnace, and I'd like to insulate that entire portion of the garage as if it were conditioned space-- so I'm inclined to prefer the next one:

    Costlier "Normal": BW closed combustion system, their model PDX2-75T6FBN. I wonder, would the the blower-managed intake spin faster to help with the altitude compensation? Even if it doesn't, this is probably not a lot more expensive.

    Now for the two "Exotic" condensing models: At current natural gas prices, they'd probably only make economic sense if they last 15+ years, AND if natural gas prices increase. (They'll both qualify for the $1500 rebates, but all the extra costs come in "up front" in year one.) At current natgas rates and our moderate usage, I see only about $700-$120 savings per year with the condensing models at current rates. But the much lower output in the "normal" model burners can barely meet our actual needs at Sea Level, and could lead to unpleasant issues in the future if their recovery rate falls with age. (I.e., the showers following drainage of the "happy" bath could turn nasty cold, partway through, if later owners make a sensible upgrade to natgas appliances for either the clothes dryer or kitchen appliances at later time.) 100 gallon HW storage tanks would require major remodeling, and that get's into a homeowner's association wrangle. I am not considering tankless, use of dual 50 gal/60gal/75 gallon gas heaters would cut into one of the garage vehicle parking spaces. But both of these condensing water heaters seems to have vastly greater recovery capabilities than we'll ever need, providing tons of "extra headroom", and definitely do it all with just a single unit.

    First up is the very new BW EFR-1-60T1206EN. It advertises automatic compensation for combustion air changes. (As in, HIGH ALTITUDE. :)) . It's a downflow burner; and their usual ceramic-lined steel is used for both the water side of the tank and the exhaust/condensation side of the condensing transfer coil. But it's larger than we need, in every way: Tank size is 60 gallons, and the smallest burner is 120KBTUH, and recovery with 90F rise is rated at 154 gallons per hour. The second rebate-qualified condensing natgas model I'm looking at is the American 'Polaris', model PG1034-1002NV. The "fit" is better: The storage tank size is only 34 gallons, even though we can easily get by with just the smallest of the 3 burners which they offer on this tank, just 100KBTU per Hour. (They do offer 130KBTUH and 150KBTUH on the same small tank, with the same 10-year warranty. That gives me some extra confidence in the 'Polaris' Stainless Steel tank, even though it might not really last any longer than Bradford-White's... the higher cost of more warranty failures could just be built into the cost of the unit.) The 100KBTUH burner is rated at a recovery rate of 130 GPH with 90F rise. Less, but more than I need-- and the smaller tank, which uses pretty much identical insulation as the Bradford-White, would probably have lower energy storage loss, too.

    The Polaris burns upwards, and then the condensation coil curls back down, drains at the bottom. It burns upwards. Although the BW model has gone through several model revisions, it seems that the current versions of both products use very similar steel-mesh burners to spread out the heat, and to assist with more complete combustion. That's not an area of difference between the two models, even though the BW fires downwards into an upwards-looping condensation loop. The BIG differences which I see are the tank/burner sizes, the tank construction, and the fixed versus variable air/gas ratio. The American tank is 444 stainless steel, and their ten-year warranty (included even with a burner 50% more powerful than the one I would choose) is impressive. The BW has another minor thing which I don't like in the electronics: It uses a single PCB for both high voltage ignition and low voltage control functions. I've had a similar Honeywell single-PCB design burn out on my EAC, wiping costly controls when a high-voltage resistor fried-- but it's not a decision criterion. I wouldn't go crazy over replacing a single, more costly board which does nearly everything except the temp Sensor.

    Here's the important question, I think: In real life, ignoring the warranty, is the lifespan of 444 stainless likely to beat the lifespan of the BW "Vitraglas" lining? In both cases, I suspect that fatal corrosion would occur from the exhaust flue condensate side first, rather than the hot water side. And is the Vitraglass tank likely to crack during a strong (but not overwhelming) earthquake, which is maybe 20-30% likely in this time frame? I would not be surprised to experience a 4.0-5.0 event in my neighborhood at some time during the next 20 years, and the flexible stainless tank might survive that. There was a 4.1 back in February, about 10 miles away, and some books did fall off of shelves here. (All the valuable stuff is anchored.) It was probably only about 3.0-3.3 within my neighborhood, but I have a closer fault which wasn't involved and didn't slip -- THIS time. :eek: ) Complex shock mounting could protect the Bradford-White unit too, but that adds a lot of $$$. I'd prefer to use just the earthquake straps and flex gas intake which code actually requires, they're cheap. My 50ft+ of iron gas supply line supply can run both the water heater and the furnace. (Kitchen an laundry are all-electric, because my DW has environmental sensitivities which preclude gas appliances within the living space. The fancy clothes washer has an electric heating element of its own.)

    I have no idea whether the BW condensing heater costs a lot less than the American's Stainless steel, or whether the Polaris could be ordered with a different venturi/manifold combination to match the altitude better. If you know, please advise. In both cases, based on the current heater's incredible lifespan and anode condition, I'll SWAG that tank failure will occur from the exhaust condensate side (rather than the hot water side).

    We are not planning to sell this house in less than 20 years. So, I'd like to know if you guys think I'd be happier, in the extremely long term, with a "traditional" for now (upgraded only when energy costs and rebate policies make it necessary); or the BW "Ultra" ceramic-lined condensing model, slightly bigger and more capable than I need; or the stainless steel Polaris.

    I will hire out the install, I'm not licensed for natgas. My sincere, grateful thanks to all advisors -- in advance. ;)
    Last edited: Oct 27, 2009
  2. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,642
    Location:
    Cave Creek, Arizona
    heater

    How much hot water do you use, or what are your rates, if you can still heat the water with the new heater and SAVE $700.00 to $1,200.00? Most gas heaters use less than that total. The usual cost for an electric heater is only $50-75 per month, and that is expensive water heating.
  3. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    If you go by the Energy Guides a conventional natural gas water heater will use about 240-250 therm/yr at around 60% efficiency factor.

    This is not the same as the burner's efficiency (which is higher.) It looks like the condensing units will fall somewhere in the 85% overall efficiency range (vs. 95% for the burner.) That will save about 75 therms/year.

    The condensing units seem ideal for large tubs. They have an output similar to a tankless unit, plus the large reservoir. You get nearly all of the benefits of whole home tankless without the hassles.

    The problem right now is "newness" and cost. In my home I want to be able to go this route in a few years once the costs drop. Since my water heater is inside an enclosed space I want to be able to use sealed combustion anyway vs. what I have now.
  4. rickst29

    rickst29 New Member

    Messages:
    9
    answers for questions above (from HJ and R.W.Bison in #1 and #2)

    OOPS! I left a typo up there which seems to have misled HJ badly. I'm writing this as a combined reply, because both posts are with respect to that key issue: the actual difference in annual saving figures.

    I mistakenly said that the saving "only about $700-$120 savings per year with the condensing models at current rates", but I meant to say "only about $70-$120 per year". HJ, it looks like you corrected the second number upwards to $1200, rather than correcting the first number downwards to $70. You're right to ask "How much water are you using ????", because what I typed made no sense for a single-family home.

    The label on my current heater shows 392 therms per year, converted into dollar figures at prices which we'll never see again. At the 2009 "energy guide" labeling price, approx. $1.09 per therm, that would be be $428 estimated cost per year. I've got a blanket on it, and quality insulation on the pipes, and the burner runs clean on the side I can see. But, with all that age behind it, gunk on the bottom probably keeps the water tank from absorbing the heat quickly- so a lot of the heat is lost into garage air space, instead of going into the water. One factor sort of cancels out the other, I think. I'll SWAG our household HW usage at about 100-150% of the energy guide labeling assumptions. It's hard to guess, because of the altitude loss and age factors on the current heater. We're definitely spending upwards of $600 per year now-- I can tell from the summer usage, when the only other gas-consuming appliance (the furnace) is completely inactive. It could be as much as $800 per year. :mad::eek:
    - - - - -

    And so, here's my main reply: HJ, I apologize for the typo which wasted your time, please do come back with more stuff. ;) RWB: Your thoughts seem almost identical to mine, except that I feel a genuine need to want to pull the trigger and do the replacement much sooner. (The $600-$800 per year is totally unacceptable, and boiling up buckets of hot water on the stove to finish filling up the whirlpool tub isn't acceptable either.)
    But my current costs aren't really relevant to the difference in operating costs between different types of new heaters. We're in total agreement here: Your 75 therms per year, times my SWAG at how much above "energy guide" labeling our usage really is, led directly to my estimate of $70-$120 per year.

    Do you guys have ideas/opinions about the difference in tank construction technology (ceramic-coated steel versus stainless)?


    One of the best things about these condensing models is the way that the flame occurs entirely within the tank, surrounded by water: over the long term, flame-underneath models loose efficiency from the lime scale and gunk which reduces heat transfer, and the heat escapes into the surrounding environment instead of going into the water. But in these units, even if gunk is present and slows down the heat transfer RATE, the heat still has nowhere to go-- except into the water! It looks to me like they won't be suffering hardly any of the age-related loss of efficiency which standard gas "burner-outside-the-tank" units suffer from.

    So, in the long term, I think that the savings difference goes up. The performance of "standard" units declines form the Energy Guide labeling a little bit more every year, through the entire life of the unit. After 5 years it's probably very significant. But if I'm right about this, then the Condensing models will stay close to the labeled efficiency, year after year.
    Last edited: Oct 27, 2009
  5. rickst29

    rickst29 New Member

    Messages:
    9
    One interesting difference between the two condensing units...

    The shipping weight of the big-tanked, glass/ceramic lined BW unit is 570 lbs. (The lengthy heat transfer/condensing coil adds a lot of surface area, and it has to be lined on both sides. That's why it's 200 lbs more than the equivalent PDX2 tank.) The American heater's shipping weight is only 150 lbs. I can wrap my arms around it and pick it up, carry it around, all by myself! The 34 gallon tank size makes a lot of the difference, and the lack of lining material makes up the rest.
    - - - -
    I think that I've talked myself into getting one of the condensing models. RWB's agreement played a big role.) And among the two, I'm leaning towards the American. Does anyone have a strong reason to disagree with this?
  6. Dana

    Dana In the trades

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    The Energy Guide labeling is based on the EF test, which is itself extremely flawed. It's based on 62gallons/day use, and will be reasonably accurate for tanks if that's your average usage. But if you use 2x that much HW your fuel use will be higher, but so will your efficiency (to a limit of ~75-80% if you're using it for space heating.) With tankless heaters it's less about total volume, more about volume per-draw, and the low end of typical as-used tankless efficiency is about the high end of high-volume-use tank efficiency.

    The sludge on the bottom of the tank doesn't have as huge an impact on efficiency as you seem to think. Most of the heat exchange in classic tanks is at the flue interface, which has more surface area than the bottom of the tank. Most newer versions have flue baffles/vanes to induce turbulence in order to improve that heat exchange:

    [​IMG]

    Some use perforated dip tube jets to induce higher turbulence at the flue heat exchanger on the water side as well.

    If you water use is truly 150%+ ahead of the EF test volumes, your as-used efficiency is probably north of 70% with a tank that tested around 0.60 in an EF test.

    Your goal is to be able to fill large tubs, but if you usually shower rather than soak, you'd do better with a standard-efficiency unit + a drainwater heat recovery heat exchanger than going with a condensing heater. You only get the benefit with simultaneous drain & hot-water flow though- batch draws typically return less than 1%. But over 50% heat recovery is typical in shower-mode. "Typical" 'mericans use ~40% of their hot water for showers, in which case you reduce the total hot water fuel use by ~20%. If showers comprise 60% of your hot water use, you save 30%, etc. (It adds apparent-capacity and quicker recovery times as well, but only for showers, not for tub fillin'.) How ever you heat your water, condensing or not, the benefit is still there for shower use. But if you're primarily tubbers (large or small) fuggedaboudit.
  7. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    rickst29,

    I'm in no rush because my annual water heater gas consumption is pretty low already, even though it is just a 0.58 EF unit. Like you I've got the tank and lines insulated. Mine is in the utility room in the lower middle of the structure, so my ambient losses aren't as great. My current estimate, accounting for winter time inlet water temps comparing to my three month summer average is that I use about 156 therm/year. Energy guide says 258 therms/yr. I have 1.5/1.6 gpm showerheads, Energy Star dishwasher, and a front loading clothes washer.

    With as much as your water heater's gas consumption is, you've got good reason to make a change, whichever way you go. (I assume you are going off the summer therms/ccf usage, not the raw bill which is usually composed largely of fixed charges.)
  8. rickst29

    rickst29 New Member

    Messages:
    9
    Agreed. I'll ask DW about pulling the trigger tonight.

    Yep, I'm using the actual therms, not the total dollars in the bill, then working backwards into a water heater "cost of use". But the killer issue is filling the tub, I've got to have a much higher 1st hour and recovery rates.

    Now-- as to which one. I'm not sure why the A.O.Smith ceramic-lined 50 gallon "Vertex" weighs so much less than very similar Bradford White 60 gallon. (The Vertex GDHE-50 shipping weight is only 255 lbs.) I can buy almost two Vertex heaters for the price of the Stainless Steel-tanked American, and of course the design and non-tank components are all being sourced from the same company. ("American Water Heaters" is just another label of A.O. Smith.) So the stainless is out of the running, even though it's probably a lot "better".

    If the wholesale price on the BW exceeds about $2300, then I shouldn't even bother anyone to get a bid-- I'll go with the lighter, cheaper AOS. Can anyone give me a hint on that?
  9. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    The most straightforward way to analyze storage type water heater energy use is to break it down among *fixed* storage losses, and variable hot water use. Pick an efficiency for the variable use (e.g. use the "recovery efficiency" from the Energy Star ratings). The recovery efficiency varies from 76-82% for example.

    Whether one uses 10 ccf/month total or 40 ccf/month total, the storage losses should be about the same for a given temperature set point and the same room temp. I quantified mine in summer as ~1 ccf/10 days while on vacation. This was an indication that the water heater blanket and insulated lines were helping.

    If I use the original 58% factor of my water heater and divide out 76% for the incremental water use, the storage efficiency would have been 76.3% originally. Working through the math this would be an energy guide loss rate of 46.5 therms/year for storage losses.

    Most of my hot water use comes from showers so I assume a ratio for winter/summer incremental water heater energy use by using X months at summer temp, and Y months at winter incoming water temp. Assuming it is all shower use I'm using a conservative assumpt since there is compounding due to mixing in the shower with colder water in winter. For me the overall factor works out to about 1.50 winter/summer for the variable portion.
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