Water Heater Questions

Discussion in 'Water Heater Forum, Tanks' started by GoldMaple, Nov 1, 2009.

  1. GoldMaple

    GoldMaple DIY Junior Member

    Messages:
    26
    Location:
    Canada
    I'm looking for a new tank style water heater and I have a few questions.

    1. The R factor of the insulation varies from heater to heater. Do water heater insulation blankets work very well?

    2. My 27 year old James Woods heater has legs but most of the new heaters do not. Is there a reason why most new water heaters do not have legs?

    3. What should I be looking for in a good water heater?

    Thanks.
  2. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    Electric, natural gas, or propane?

    Yes, the blankets can help considerably, particularly on tanks with only an inch or so of insulation. My current 50 gallon gas water heater is only R8 with 1" of insulation. I added an R6.7 blanket. This reduced tank losses by about 10-15 therms/year. So it will pay out in less than 18 months.

    If I purchased an R24 insulated water heater, I might not even add the blanket as the payback would be over 10 years. (The numbers might seem odd, but I accounted for the head and base of the tank in my calcs which cannot be blanketed.) I wanted an R10 blanket for my less insulated heater, but none were in stock locally at the time. It would have added condiserably to the circumference, so the R6.7 was probably a better fit (literally.)

    I don't know with respect to the legs. Mine has short legs. The negative of legs and other projections from a tank is that they conduct heat away from the vessel, increasing storage thermal losses.

    Since your water heater is so old, you must have pretty mild corrosion/sedimentation conditions in your hot water. That's good and suggests that it might make sense to invest in a long life tank, because you might double it.

    Assuming that you aren't wanting to do power venting/sealed combustion or higher efficiency condensing types, I suspect you want to invest in one with known high reliability, well insulated, and with good overall efficiency. I suspect something like this would last you a very long time.

    For gas the Bradford Whites/Rheems/GE's are generally well liked because they have a better air induction system for the FVIR regs. They draw air from openings in the sides. The Whirlpool/State/A.O. Smith/American Water Heater types have small openings for air, located on the bottom of the tank. This can result in inadequate draft with associated thermocouple failure as well as a failing gas valve/thermostat.
  3. GoldMaple

    GoldMaple DIY Junior Member

    Messages:
    26
    Location:
    Canada
    Gas Heater

    Thanks! I'm looking for a 40 gallon natural gas water heater. All of the big box stores here in Canada sell tanks with very little insulation and I've been reading blogs suggesting that the big box stores sell a cheaper line so they can fit a price point. I'm willing to spend a little more to get something that might last another 27 years..... Rheem and Bradford White keep coming up as preferred water heaters so I'm already leaning in that direction.

    As for the legs on the heater I'm just a bit concerned that if I get a heater without legs and my floor is not perfectly flat that it could rock. With 3 legs it will not rock at all. The basement floors in my house are not flat.

    Also, what do they make the flat bottom tanks with? Will they rust? My basement floor does not have a vapor barrier under the concrete so moisture could collect under something that is directly on the floor.
  4. Cass

    Cass Plumber

    Messages:
    5,980
    Location:
    Ohio
    One other thing...don't expect your new heater to last 27 years...Brad White first then Rheem...
  5. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    heater

    1. Many manufacturers specify NOT to use a blanket.
    2. Unless your heater is hot to the touch, there is almost no heat loss throught the jacket, and definitely not enough to be affected by a blanket.
    3. Gas heaters get most of their standby loss up the center flue where a jacket does absolutely no good.

    Therefore, it you want the most efficiency, you need a heater with a mechanical damper on the flue that closes when the burner is not operating.
  6. No blanket, they haven't tested it out and they have no product to sell as an add-on. To limit liability they won't comment except to say "it's fine without any more insulation." To limit time wasted, they won't allow any discussion either.

    This has been my experience with _Electrical_ HW tank manufacturers.
    About gas, no comment.

    It IS possible that someone will overinsulate something.
    Not likely in the average household, but it's still a possibility.
    Extra Insulating an electric water heater is certainly possible, and you might like the result.
    Or, you might find you are not satisfied after doing the exercise.


    Heat is transferred in all directions to all surrounding objects. Just like the sun sending heat out to all the planets. We get heat radiated from the sun. HW tanks are a permanent source of heat energy for their surroundings. There IS some heat lost (transferred). The tank does warm its surroundings a little bit.

    Insulation that covers most of the HW tank will have an impact, reducing the amount of energy that is radiated out to the surroundings.

    Whether it's worth your while is another question, and the answer is not easy to calculate: formulas purported to justify payback are not the whole picture. Don't expect a big change. Get a good heater to start with.
  7. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    On a gas heater, you cannot put any blanket on the top area at all.

    In 2003, WH companies had to make significant changes in the burner area to comply with FVIR, and invariably that tended to make the water heater taller. Since 4 extra inches of height can cause signigicant install issues for a large population of existings, they usually opted to remove the legs, to keep the overall height about the same as the old ones.
  8. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    Wouldn't mean much as they do what gives THEM the fewest problems, consumer be damned. The most likely problem from insulating is that some will not notice small leaks as quickly with an extra layer.

    That is completely wrong, a common layman's misperception of heat transfer. One could make the same claim about home walls and ceilings and be equally wrong.

    Double the effective R value, cut the wall losses in half. Doesn't matter whether it feels hot or not. If you drop the outer surface from 76 F to 73 F in a 70 F room, you've still reduced the wall losses by roughly half. Once you get to an R value in the neighborhood of 16+ there is much less incentive for a blanket or additional insulation. But in the R8 range the payback is rapid.

    Yes, there are other sources of loss, such as the chimney/flue, relief valve & discharge piping, and thermosiphon/conduction in the inlet/outlet lines.

    There is definitely some waste from draw up the chimney, but from what I can tell on mine, the pilot roughly balances this. Haven't had a power vent for comparison. With a power vent you can expect higher maintenance and/or earlier replacement for the efficiency gain of the damper. They cost considerably more but they tend to have more insulation to begin with.

    That is misleading though. It is already insulated so it is not insulation that is the problem, but adding additional layers there could interfere with the draft or cause other issues. (I doubt that this applies to sealed flues other than needing some offset.)

    And the area of the top is about 10% of the wall area. So while you can't cut it's losses, it is a small portion of the total.
  9. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Below is from the Rheem Fury use and care/install manual. It says don't put on a blanket, but if local code requires you to use a blanket, don't put it on top.



    Insulation Blankets
    Insulation blankets, available to the
    general public, for external use on gas
    water heaters are not necessary. The
    purpose of an insulation blanket is to
    reduce the standby heat loss encountered
    with storage tank heaters. This water
    heater meets or exceeds the ​
    National
    Appliance Energy Conservation Act
    standards with respect to insulation and
    standby loss requirements making an
    insulation blanket unnecessary.
    The manufacturer’s warranty does not
    cover any damage or defect caused by
    installation, attachment or use of
    any type of energy saving or other
    unapproved devices (other than those
    authorized by the manufacturer) into, onto
    or in conjunction with the water heater.
    The use of unauthorized energy saving
    devices may shorten the life of the water
    heater and may endanger life and property.
    The manufacturer disclaims any
    responsibility for such loss or injury
    resulting from the use of such
    unauthorized devices.

    CAUTION: If local codes require the
    application of an external insulation
    blanket to this water heater, pay careful
    attention to the following so as not to
    restrict the proper function and
    operation of the water heater:​
    ● ​
    Do not cover the operating or warning
    labels attached to the water heater or
    attempt to relocate them on the exterior
    of insulation blanket.

    Do not apply insulation to the top of the
    water heater. This will interfere with the
    safe operation of the draft hood.

    Do not cover the burner access door,
    jacket door, gas control (thermost at)/gas
    valve or pressure and temperature relief
    valve.

    Do not apply insulation to the bottom of
    the water heater or the area where the
    combustion air inlet openings are
    located. This area must be unobstructed
    so as not to restrict combustion air flow
    to the burner.

    Inspect the insulation blanket frequently
    making certain it has not sagged and is
    restricting the air flow to the combustion
    air inlet openings (perforation holes)
    located around the lower perimeter of
    the water heater jacket. This could result

    in an unsafe operating condition
  10. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Your heater outlasted 96% of NG WHs. I doubt you'll do as well next time.:(
  11. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    It does not say "don't put on a blanket." It claims they are unnecessary as the vessel already complies with the most basic regulatory requirements. That does not mean it is the optimum or cannot be improved--as any one competent in analyzing heat transfer can tell you.

    Pretty much standard lawyer boilerplate in their wording. They simply say they won't cover damage caused by the presence of a blanket.

    What's really telling is that they have to allow for the blanket and explain the reasonable concerns they have for those using them. Obviously the air/burner access should not be blocked. Checking for sags and all that is important. Not blocking the top flue is important. This same information is generally found on the jacket's packaging from what I recall of the install.
  12. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,631
    Location:
    Cave Creek, Arizona
    blanket

    quoe; The most likely problem from insulating is that some will not notice small leaks as quickly with an extra layer.

    Unless water has become as light as air, it WILL drain down to the lowest point and run onto the floor. I have never seen any "small leak", and very few, if any, big ones which appear "through the heater jacket" which is what the blanket covers. You do not "need" window sun blocks in your car, but you can have them. The same is true of heater blankets. If you want to spend the money on them, go ahead, but do not expect spectacular results from using them. And, do not expect me to tape it together after I have to cut into it to service the water heater.
  13. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    I wish we had some numbers, but I haven't seen anything. Regarding the touch test, I understand the physics of heat transfer ( sort of!). But if the water is 130º and the garage is say 40º, and you touch the side of the tank, and it feels much closer to 40 than to 130, then I am willing to live with whatever heat loss is taking place there, as opposed to the ugly dirt collecting mess of a blanket. If I wanted save a ton of energy on my wh, I would look into direct vent, or power vent, or maybe a damper. But my hot water does not cost me very much right now, so I am not losing any sleep over the issue.

    I assume algore has an SUV sized water heater, while Ed Begley is probably taking sponge baths with a gallon of water solar heated on his back porch. Things sort of balance out!
  14. Runs with bison

    Runs with bison Member

    Messages:
    892
    Location:
    Midwest
    It's pretty easy to untape it and set it aside. Let the homeowner reinstall it. But if you choose to be destructive, expect to pay for it in several ways.

    As far as "spectacular results" that's a strawman argument. :rolleyes: The results are modest, but measurable.

    That's an incorrect approach. If the water heater does not feel much closer to 40 than 130, then it is really awful--essentially uninsulated. The same is true in your home with regards to walls or window. If you find a section of wall that is particularly cold during winter, it most likely has little/no insulation in that section or it has air movement/infiltration in gaps there, etc.

    With R2 effective one would expect a wall temperature of about 40 + (130 - 40) / (2) = 85 F. In that case losses would be nearly as great as my actual water heating load (minus storage losses) for a family of four. Reduce wall losses by 4X by going to R8 and the temp falls to ~51 F. Cut wall losses by 2X again by going to R16 and you have a wall temp of less than 46 F. The later is precisely the sort of case we are talking about.

    And all of those are possible at a much higher installed cost than a $15-25 water heater blanket. Depending on the insulation level of a given tank, the jacket is likely to pay for itself much more rapidly and much more easily.
  15. GoldMaple

    GoldMaple DIY Junior Member

    Messages:
    26
    Location:
    Canada
    Legs

    For those of you have installed many water heaters what do you think about the difference between those with 3 legs and those that have a flat base? Do you find that when the basement floor is uneven and you have to install a water heater with no legs that it wobbles? This is my concern given my basement floor is very uneven....
  16. Dana

    Dana In the trades

    Messages:
    2,840
    Location:
    01609
    That's a pretty lousy model of what to expect for a surface temp, since it presumes both a low-emissivity finish, and a boundary layer of air that's ~R2, neither of which is a good assumption, but the essential point is correct- if the surface is at all warm it's pretty lossy, and an insulation upgrade is cost-effective.

    Even at R2 the surface temp should be much close to room temp than the mid-point between room & water. The aspect ratio will affect convective losses at the air/tank boundary, but even 10F over room temp will drive significant air. The infra-red emissivity of the finish will affect the final temp as well, and a low-E finish would result in a somewhat higher surface temp while being slightly less lossy overall.

    But here we're well into "WHO CARES?" territory again, eh? ;-)

    Bottom line- you don't need to measure the surface temp to know if it needs more insulation. In a 40F garage it ALWAYS needs more insulation, since it's at least 25F colder in the room than when the unit's efficiency was measured, and the standby losses will be dramatically higher than when it's in an 80F carport in St. Croix. Standby losses are everything when it comes to tanks.
  17. Thatguy

    Thatguy Homeowner

    Messages:
    1,459
    Location:
    MD
    Standby loss of a 70s elec. WH:
    5 minutes on every 5 hours [75w], and after a blanket,
    5 min/7 hrs [50w].
  18. Dana

    Dana In the trades

    Messages:
    2,840
    Location:
    01609
    So a 25W savings over 8760 hrs/year is 219kwh/year. At $0.12/kwh that's $26+/year in after-tax ROI. (The internal rate of return is doin' way better than yer 401K, eh? ;-) )

    Some investments are no-brainers.
  19. From my own extensive research in this topic, I'll come in on the side of those who say that

    1. one CAN add a blanket, it's never forbidden.
    And, manufacturers always avoid answering this question directly.
    They find cute ways to say things that could EITHER mean
    "we neither RECOMMend nor dis-recommend" or
    "we actively discourage"
    Then when you try to pin them down to which one of these two interpretations is right they get really dodgy.
    There is no point calling their 1-800 phone line about this topic.
    It leads to a never ending series of tautologies, an infinite loop of self-referring tautologies.
    Try it if you have spare time for this kind of fun.




    From my own extensive research in this topic, I'll come in on the side of those who say that
    2. heat transfer is a proven provable phenomenon that does not in any way correspond to the average person's finger feel.



    In my first post above, I mentioned that it is possible to overinsulate something. To exaggerate this, think of a refrigerator wrapped up in a plastic bag. It will overheat because waste heat will be trapped. With WH it's a different story because they have relief valves, but the idea is the same.


    So, from my own extensive research in this topic, I'll come in on the side of those who say that
    3. increasing the R value of the walls is a good thing to do.


    -david
  20. rickst29

    rickst29 New Member

    Messages:
    9
    Don't forget! Code (and safety) probably REQUIRES some kind of base.

    I don't know the exact code requirements of your Province/City, or even your Nation. But in the USA, gas fired burners and pilot lights must be installed at least 18" above garage and basement concrete floors, and I'll bet that the same is required in Canada (with maybe a slight change in the height requirement).

    My recommendation would be to buy a flat-bottomed model, and then build a wood platform (painted with waterproof paint, of course), because it will conduct a lot less heat to the floor and surrounding air than than the steel legs will. If you build it yourself, you can also cut the length of the legs so that they end up with the top of the platform exactly level, perfectly matching the location you have chosen on your non-flat floor.

    Note: You might also need a leak pan with a drain, sitting on top of your platform. Again, many codes require such a pan, and they'll also require that it's diameter needs to be wider than the tank by a code-specified "splash" distance.
    Last edited: Nov 7, 2009
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