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Thread: Water heater insulation

  1. #31
    In the trades Dana's Avatar
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    Quote Originally Posted by nukeman View Post

    Additional insulation does help to some degree. However, heat is like water or electricity and tends to take the path of least resistance. So, say you start with a tank with no insulation (inside or out). The most heat loss will be out the side walls as that has the most surface area. Now say you start insulating those side walls. Now, the largest fraction of heat loss will be out the top/bottom of the tank. Then you start insulating that. Pretty soon, heat carried from the tank up the copper piping and through the water will dominate the losses. The total losses will reduce as insulation is added, but where the majority of the losses occur will shift depending on what paths you close off by adding additional insulation.

    So, adding insulation to the side walls will always help to some degree but returns are diminishing. There is a point where there won't be a lot of benefit to adding more insulation to the walls as the majority of the heat loss will start being in other directions/modes. Think of a house. Most of the heat goes out the attic. Although going from R30 to R100 in the attic would help, but the impact may be small if your house is covered with single pane windows and has uninsulated walls. My point is you have to look at the whole system.

    If the WH is in a conditioned space, then it doesn't even matter (at least in non-summer months) as the heat loss will go into warming the house. If it is in a garage, be sure to insulate the pipes, etc. while you are at it.

    Anyway, that is the take from someone with a couple fancy/expensive degrees.

    The heat loss from the tank & plumbing does matter, even in conditioned space, even in heating dominated climates, not just in the garage....

    Unless you're happy heating your house at the marginal efficiency of a tank HW heater, and don't mind wasting time & water waiting for the hot to arrive, all the while dumping the BTUs of the tepid water in the distribution plumbing down the drain. It adds up- not gonna break the bank, but R2-R4 pipe insulation is cheap stuff, and the investment goes NPV+ in a very short time frame.

    The standby heat loss from near-tank plumbing is typically more than half that of the tank walls in a marginally insulated tank, so you gain as much or more benefit out of insulating the near tank plumbing as you might from doubling the R-value of the tank walls. It's not a BAD thing to add more insulation to the tank walls, but the benefits are slight if the heat loss is still dominated by plumbing heat losses. (Do both, but if yer only gonna do one, put R4 on the near-tank plumbing.)

  2. #32
    Nuclear Engineer nukeman's Avatar
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    I'm talking from an electric point of view. Heat coming from the elements in the WH has the same efficiency as other electric resistance heat (baseboard, aux. strip heater, electric furnace, etc.). In addition, the dT is less in general when in conditioned space, so the heat loss is less with the same amount on insulation. I am not saying to not insulate when in a conditioned space, but just that it is not as important to go crazy with it. If your on gas, then you are better off getting the heat from the boiler/furnace, but you still retain some benefit of 'losses' of a WH that is placed inside the thermal envelope.

    As far as the pipes, many times you can only insulate the entire run when the house is built. You may be able to insulate some of the run with an unfinished basement/crawlspace after the fact. If your basement is finished, then you can only insulate the pipes near the WH, which does nothing for the rest of the pipes cooling off. It still helps standby loss, but you are still going to wait for hot water.

    The real point is that the "wasted" heat in a conditioned space isn't really wasted. It may not be as efficient as your furnace, but you still get a benefit. If the WH is in the garage or attic, you can kiss those losses goodbye.

    So, do what you can for insulation. It just isn't worth tearing out walls/ceilings just to insulate the pipes. I personally see a bigger benefit to insulating the pipes that you have access to than to add a blanket to the WH. At some point, you have to say "good enough." I do think we are saying the same thing as far is controlling the losses for the system as good as you can instead of just the losses at the tank walls.

    As I was saying for the attic example, R100 would reduce total losses compared to typical attic insulation, but people don't use R100 there since:

    1. the additional cost may take forever to recover (in most locations)
    2. the benefit is reduced unless the entire house is superinsulated and tight

    This is like putting all of your focus on insulating the WH, but leaving the pipes exposed.

  3. #33
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Doherty Plumbing View Post
    I was correcting you on implying that R10+R8 is better then R18 insulation.
    Then you were "correcting" a figment of your imagination as that is not what I said.

  4. #34
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    Quote Originally Posted by Ian Gills View Post
    I cannot be bothered to read all the previous back and forth.

    But it is simple common sense not to use an insulating blanket with a gas water heater.

    The blanket is a fire risk. Period.
    Baloney. Period.

  5. #35
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Dana View Post
    The heat loss from the tank & plumbing does matter, even in conditioned space, even in heating dominated climates, not just in the garage....
    Yes, and it's more of an issue in more southerly climes where there is less need for winter heating and more need of AC. That extra heat has to be removed during the cooling season. While the COP is pretty good for AC there is still a cost.

    Another factor is that the utility space is not really the most useful place to have running hot in winter. Any heating gain from tank losses is fractional. This is similar to the unwanted heat from incandescents vs. CFL's. Much of the heat from light bulbs is not going to a useful location for making the home comfortable during the winter.

    One of the major improvements I made in the comfort of this home and the performance of the HVAC was in the utility room: insulating and sealing ductwork, insulating pipe, and blanketing the water heater. The utility room is no longer hot in winter and cold in summer...it's also not collecting dust anymore. I've measured the effect a few times and the delta T compared to adjacent spaces has been reduced by 1/2-2/3. Short circuiting of the conditioned air in that space has been minimized, and that duty is now going where it is intended. The corners of the home are now running closer to the thermostat setpoint (in a central hall above the utility space.)

    Quote Originally Posted by nukeman
    As far as the pipes, many times you can only insulate the entire run when the house is built. You may be able to insulate some of the run with an unfinished basement/crawlspace after the fact. If your basement is finished, then you can only insulate the pipes near the WH, which does nothing for the rest of the pipes cooling off. It still helps standby loss, but you are still going to wait for hot water.
    True enough, but I've only got a single run that I can't get much access to. The ceiling of the basement utility room is open as are some storage areas. From there I succeeded in sliding insulation down much of the bathroom runs that were otherwise concealed by drywall. From the fixture direction I've had to install two access panels because of plumbing issues--so that allowed me to insulate much of the missing sections.

    The one major area I can't yet insulate is the kitchen run that goes another route. It runs next to some ductwork behind drywall, but I will probably have to access part of the ductwork next summer anyway for two or three new register runs and a new return (to properly balance the system.) That will provide an opportunity to finish the job.

    The reduction in wait times for hotwater with insulated pipes is noticeable. Plus it is worth a degree or two at the tap.

  6. #36
    Senior Robin Hood Guy Ian Gills's Avatar
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    Quote:
    Originally Posted by Runs with Bison
    I cannot be bothered to read all the previous back and forth.

    But it is simple common sense not to use an insulating blanket with a gas water heater.

    The blanket is a fire risk. Period.

    Baloney. Period.
    The last time anybody made a list of the top hundred character attributes of Americans, common sense snuck in at number 79.

    Heck, use a blanket on a gas water heater but just make sure:

    - The space between the base of the water heater and the floor remains unobstructed to allow for proper airflow. As time passes, the blanket may sag and obstruct the air passage resulting in unsafe water heater operation.

    - Do not apply an insulation blanket to the top of the water heater as this may obstruct the draft hood.

    - Do not cover the temperature and pressure relief valve, any labels or instruction materials applied to the water heater. These labels must remain visible for reference by the user.

    - Do not cover any access panels leading to burner compartments. Do not cover the thermostat controls, or doors on the water heater.

    Just drop the blanket.

  7. #37
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Ian Gills View Post
    The last time anybody made a list of the top hundred character attributes of Americans, common sense snuck in at number 79.
    Apparently for Brits it came in about 179.

    These labels must remain visible for reference by the user.
    More baloney. The information on the labels is useful, but there is nothing stopping anyone from recording it or removing the jacket to see it if necessary. I generally record such info in my manual anyway for my appliances--I did so before putting on the jacket because I try to anticipate and avoid potential problems. Often time serial numbers are on the back of the device somewhere in a place that is a PITA to access when needed. So I record it on a sheet with my documentation before I slide it into place. That way if I have to call for parts I have everything I need in hand. That's just common sense...as is making a small investment that returns north of 50% per year. But, hey, if you can find better returns than that I'm all ears.

    Time to revise that list of character traits.

    BTW, last night, just for grins I took a portion of the blanket that I had cut away for the gas valve, and I tried setting it on fire. The insulation itself did little but blacken/turn gray. The facing would sort of burn with some effort...but not in a meaningful way. Certainly not in a way that would allow it to propagate.

  8. #38
    Senior Robin Hood Guy Ian Gills's Avatar
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    If I was a home inspector, and I saw a blanket around a gas water heater I would go absolutely crazy.

    I'd jump up and down.

    I would put on a frock.

    I'd wave my fists in the air.

    And I would shout.

    I would then remind the client that they were not obliged to do anything that I told them.
    Last edited by Ian Gills; 12-17-2009 at 08:29 AM.

  9. #39
    In the trades Dana's Avatar
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    Quote Originally Posted by Ian Gills View Post
    If I was a home inspector, and I saw a blanket around a gas water heater I would go absolutely crazy.

    I'd jump up and down.

    I would put on a frock.

    I'd wave my fists in the air.

    And I would shout.

    I would then remind the client that they were not obliged to do anything that I told them.
    You have YOUR religious rituals, I have mine....

  10. #40
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Ian Gills View Post
    If I was a home inspector, and I saw a blanket around a gas water heater I would go absolutely crazy.

    I'd jump up and down.

    I would put on a frock.

    I'd wave my fists in the air.

    And I would shout.

    I would then remind the client that they were not obliged to do anything that I told them.
    And if I were a home inspector and saw a standard gas storage unit without a blanket I would suggest that the purchaser consider installing one. It's a value added thing.

    p.s. I would probably also warn them about toilet tanks that failed to make three point contact (with resulting tank rock.)

  11. #41
    Master Plumber Redwood's Avatar
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    Bradford White Service Bulletin
    Insulation Blankets (#112)

    During times of energy crises and rising fuel costs, property owners tend to be more energy conscious. Water heater blankets are often considered for heat loss and conservation purposes.

    Blankets for older fiberglass insulated electric water heaters make sense, especially since electricity is a much more expensive method to heat water than gas. Most electric water heaters insulated with foam (R 8.33 or higher) meet ASHRAE standards for performance (efficiency and standby loss) when tested according to Department of Energy procedures.

    Many experts argue that heat loss in a gas water heater goes up the flue and therefore a blanket accomplishes no purpose.

    Some local codes and utility company regulations may prohibit insulation blankets. Too often, the Do-It-Yourselfer has good intentions but unknowingly creates hazards by:

    • Covering safety warnings and operating instructions. (These labels are not to be removed from the heater and placed on the blanket or elsewhere.)
    • Covering controls, access areas, shut off devices, temperature and pressure relief valves, etc.
    • Blocking air passages required for combustion or draft resulting in unsafe operation.

    Consequently, the water heater manufacturer does disclaim any liability for problems associated with the use of insulation blankets. Bradford White Service Bulletin #112 Insulation Blankets
    Somehow I think Ian Has come across with some great wisdom that the engineers at Bradford White seem to share...

    I'll agree with them also.

    By the way I ate a Bison Burger when I was at Cabela's the other day...
    Not to shabby I can see why they were pushed to the brink of extinction...

  12. #42
    DIY Senior Member Runs with bison's Avatar
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    Quote Originally Posted by Redwood View Post
    Somehow I think Ian Has come across with some great wisdom that the engineers at Bradford White seem to share...

    I'll agree with them also.
    Why would you agree with something that is so easily and demonstrably false?

    Who says an engineer wrote it? In fact it is written in a fashion that indicates a marketing/legal monkey was the author. An engineer worth his salt wouldn't be so stupid as to write: "Many experts argue that heat loss in a gas water heater goes up the flue and therefore a blanket accomplishes no purpose." Actually, no expert would state it that way, because it is patently false as I've demonstrated half a dozen times here already.

    The blanket added to a 1" insulated tank does roughly the same thing as the 2" thick insulation of the "high efficiency" variants.

    Perhaps the same marketing monkey that wrote the drivel could add, "Many experts argue that heat loss loss in a gas water heater goes up the flue and therefore our high efficiency water heaters with extra insulation actually accomplish no purpose." Of course that would be a lie as testing provides efficiency factors that illustrate a difference.

    I've yet to see any analysis from an actual expert in heat transfer stating what these clowns are claiming. In fact, those of us who have designed quite a bit of heat exchange equipment know that the claim is false. I've done the calcs and they are in agreement with the sort of differential in EF that the manufacturers report. If they can produce a fellow "expert" in heat transfer design I would be happy to discuss the matter with him/her.

    And of course there is this beauty:
    "Most electric water heaters insulated with foam (R 8.33 or higher) meet ASHRAE standards for performance (efficiency and standby loss) when tested according to Department of Energy procedures."

    Well, duh! That's because the standards were set as a minimum so that 1" of insulation would just make them passable in most cases. There's a big difference between minimum, optimum, and maximum efficiency. Why is that so hard for many of you laymen to understand?

  13. #43
    Master Plumber Redwood's Avatar
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    Well Mr Bison Burger...

    The way this layman sees it is I don't have the Title DIYer underneath Redwood at the top of my post. Come to think of it neither do most of the people whom you are arguing with...

    The losses up the flue are significant much more than you can possibly imagine...

    If you want real gains in avoiding stand by heat losses I would suggest getting your thinking away from atmospheric vented gas water heaters and suggest you take a look at power vented and some of the newer condensing water heaters where the losses up the flue are very small indeed. Some real gains to be made there my friend...
    But hey what would I know?
    I'm just a plumber...

    I'll stand by my signature....

  14. #44
    Journeyman & Gas Fitter Doherty Plumbing's Avatar
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    Quote Originally Posted by Redwood View Post
    Well Mr Bison Burger...

    The way this layman sees it is I don't have the Title DIYer underneath Redwood at the top of my post. Come to think of it neither do most of the people whom you are arguing with...

    The losses up the flue are significant much more than you can possibly imagine...

    If you want real gains in avoiding stand by heat losses I would suggest getting your thinking away from atmospheric vented gas water heaters and suggest you take a look at power vented and some of the newer condensing water heaters where the losses up the flue are very small indeed. Some real gains to be made there my friend...
    But hey what would I know?
    I'm just a plumber...

    I'll stand by my signature....

    Bison obviously just can't admit when he's wrong. He's one of those engineering types who sits in an office and imagines situations in perfect lab conditions where their math actually works. I think he needs to go work out in the field for 5 years before he should try and argue things he knows nothing about.

    Bison go fire up a gas HWT and then let it cool for 20 mins. Then stick your hand over the flue opening and tell me if you feel heat dumping out or not?

    For example Bison why do boiler manufacturers put automatic flue dampers on their boilers? TO DRIVE UP THE EFFICIENCY RATING!. They don't just put thicker insulation around the boiler and call it a day. Because any old idiot could understand that the STEEL flue and baffles would absorb quite a bit of energy and they would then just dump that energy out the top of the boilers flue opening into the colder surrounding.

    You need to start thinking logically bro and stop over thinking everything.
    Last edited by Doherty Plumbing; 12-17-2009 at 10:45 PM.

  15. #45
    DIY Senior Member Runs with bison's Avatar
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    When it comes to heat transfer and heat exchanger design you folks are the laymen, not this DIY'er. Doing the actual plumbing connections is your area of expertise. Heat transfer, reactions, mixing, and fluid flow are mine.

    It doesn't matter if the losses up the flue are several times greater, reducing losses along the walls still increases efficiency as well. You must complete the thought if you want to get the correct answer.

    I'm not disputing the flue losses because they don't change the external wall losses. That's a strawman argument on your parts. What I'm disputing is your assertions that with 1" of insulation there are no remaining wall losses. They don't go to 2" of insulation on various tanks for no reason. It costs them money to do so, but they need to bump up the efficiency a few percent. Oh...wait a minute, that's the whole basis of my argument now isn't it?

    Doherty Plumbing said:
    You need to start thinking logically bro and stop over thinking everything.
    They are called calculations. It's what you do to determine if a hypothesis has merit or not. The areas of the tank surfaces on my 50 gallon (at the metal insulation cover) are roughly:
    21 sq. feet wall, 4 sq. feet on both ends, 3 sq. feet for central chimney.

    Of the ends, half can be considered uninsulated combustion dome, half insulated head. So the flue/combustion surface is around 3 + 4/2 = 5 sq. ft.

    Relative R values should be around R8 1" insulated wall/head and about R1 for the tank wall without burner operation. It's a chimney and that complicates matters. Also complicating it is the presence of the pilot. So the heat transfer coefficienct would increase because of draw, but the air is hotter than ambient because of flow path and pilot combustion heat, which would reduce overall delta T and losses for a given coefficient. Call it a wash.

    UA's work out to:
    wall = 21/8 = 2.6
    top head = 2/8 = 0.25
    bottom head/flue = 5/1

    Sum = 7.85

    No surprise, the flue losses are dominant. However, what is also obvious is that there is room to cut the wall losses. And that is in fact what is targeted with the blanket.
    UA of wall with R10 blanket = 21/(8+10) ~ 1.2
    net reduction in UA = 2.6 - 1.2 = 1.4

    Result would be 1.4/7.85 = 18% reduction in these storage losses.

    One must also divide by the burner efficiency (for the mode the tank will be in when it fires just to bump the temp back up to set point...and that will be very low, something less than the 76% or so that it gets in cold tank recovery mode.)
    Last edited by Runs with bison; 12-18-2009 at 01:06 PM. Reason: typo

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