Water heater insulation

[Cass]

Seems to me that this will equate to savings. Heat loss decreases as the temperature difference between inside and outside the tank decreases (assuming everything else stays constant). The purpose of the insulation is to trap heat between the insulation and the tank, raising the temperature on the outside of the tank and decreasing the temperature difference. Seems to me that this is how all insulation works (e.g. attic insulation).

The insulation has a loss rate...it slows the rate of heat loss..and as you approach the max loss rate the savings plummets and then the other part of the equation is the amount of use the heater gets...the more it is used the less savings there are...

[nukeman]

Additional insulation will always reduce the heat loss in that direction with everything else being equal. However, there is a point where the additional cost of the insulation will not be recovered by energy savings.

In addition, there is a point where you will not see a benefit to the additional insulation as the losses in the other directions (bottom of tank, top of tank, conduction through the piping, etc.) will dominate the losses.

Most modern tanks benefit little from the blankets compared to the older tanks. I know that the manual for my GE/Rheem (electric) specifically states that a blanket is not needed.

Where is your tank located? Garage or in conditioned space? If inside, the dT is lower during the winter (compared to a garage/attic) and the heat loss does go into warming the house, so the heat that is "lost" isn't really lost.

[Dana]

Additional insulation will always reduce the heat loss in that direction with everything else being equal. However, there is a point where the additional cost of the insulation will not be recovered by energy savings.

In addition, there is a point where you will not see a benefit to the additional insulation as the losses in the other directions (bottom of tank, top of tank, conduction through the piping, etc.) will dominate the losses.

Most modern tanks benefit little from the blankets compared to the older tanks. I know that the manual for my GE/Rheem (electric) specifically states that a blanket is not needed.

Where is your tank located? Garage or in conditioned space? If inside, the dT is lower during the winter (compared to a garage/attic) and the heat loss does go into warming the house, so the heat that is "lost" isn't really lost.

True-dat!

Putting a blanket on the already-insulated tank if you haven't insulated the near-tank plumbing (including the temperature/pressure valve plumbing and the cold water feed) to within the first 6' of the tank to at least R4 (5/8" wall closed cell foam or similar).

Temperature actuated flue dampers can at least keep most of the center-flue heat losses within the room (heating up the space around it), as opposed to sending the bulk of it up the flue (along with conditioned-space air 24/365, when you really only need/want the flue drafting to dispose of combustion exhaust at a MUCH lower duty cycle- much closer to 1% of the time than 100%.)

[Runs with bison]

While the manufacturers might claim there is no need for the blanket, they qualify that by saying it is not needed to comply with federal regs.

There is in fact a substantial benefit to the blanket, at least when the tank insulation is only R8. The loss rate with and without blanket can be calculated. This is also why you see some tanks in a series listed as "high efficiency" with 2" vs. 1" of insulation. 1" of foam = R8, that's the normal baseline now for a 0.58 or 0.59 EF tank in the 40-50 gallon size although some other tanks have 2"--probably to help prop up what would otherwise be too low of an EF. The respective 2" foam tanks in 40-50 gallon sizes are about 0.62. It's not hard to see how a small price differential for the extra insulation quickly pays out.

Now, if the tank already has 2" of foam on the sides, then the benefits of adding a blanket will be much less for the area covered and space considerations can predominate. Looking at this in terms of deltaU: (1/8 - 1/(8 + 10) = 0.069 vs. 1/16 - 1/(16 + 10) = 0.024, therefore the savings are a little over 1/3rd as much as in the base case. As a result the minimum return is likely to be about 17% annually...instead of around 50%. If the tank lasts the minimum 6 years the additional insulation worst case result is break even over the lifetime...better if the tank lasts longer and/or if the blanket is removed and reattached to the replacement tank.

I agree about tank projections needing insulation, but you have to be very cautious near the flue. If you put flammable or meltable material on the top piping within 6" or so of it, you can create a serious hazard. (I need to go down to an industrial insulation supply house to get some proper material for this short section.) It's of course much easier to insulate the T&P and discharge line.

The argument several are making is like saying improving attic insulation from R19 to R30 or R40+ won't help because other areas (such as windows or infiltration) loses/requires so much heat.

The "at least initially" part is just plain wrong. The resistance added by the insulation continues indefinitely. There may be some degradation of the insulation over time, but it is not going to go anywhere near zero unless it is saturated with water.

More interesting is "The insulation has a loss rate...it slows the rate of heat loss..and as you approach the max loss rate the savings plummets and then the other part of the equation is the amount of use the heater gets...the more it is used the less savings there are..." The first part isn't really clear. I think what was intended was to say that as the overall insulation value increases the total losses become less and less so that the incremental savings plummet. This much is true and is the same as effect as gas mileage savings over a fixed distance. Going from 12 to 24 mpg saves a lot of gas. Going from 24 to 48 mpg saves less gas even though mileage doubles in both cases.

The second part is incorrect. The wall losses are essentially fixed: If you put twice as much water through the tank at the same setpoint the wall losses for the year are essentially the same (okay, there is a slight difference due to more time spent in cooler recovery mode.) The overall efficiency factor of the tank changes...but that is why EF's are reported for a single usage standard. The savings are still essentially the same for doubling the insulation value, even if you double or halve the water rate through the tank.

Note: the above discussion about benefits applies to standard gas storage water heaters primarily. Electric tanks seem to have thicker insulation (R20 to R24.)

[Doherty Plumbing]

As a quick test, I wrapped part of the heater. Sticking my hand between the fiberglass and the outside of the tank results in a significant warmth. Much warmer than the un-wrapped surface of the tank.

You were likely just feeling the heat being released by your body getting trapped under the insulation. I wouldn't attribute this to the heat loss of the tank.

You need to use a remote thermometer.

[Runs with bison]

You were likely just feeling the heat being released by your body getting trapped under the insulation. I wouldn't attribute this to the heat loss of the tank.

Wrong. Any time you put significant insulation over a primary source you will find that the temperature between is now closer to the source (in this case the water heater tank.) This is introductory heat transfer. Seriously, all animosity aside, if they offer trades courses in this I think you would both benefit from and enjoy them--plus I think it would help your customers in the long term. You seem to have a strong interest in the subject, and that is a positive thing. If you mastered the fundamentals of heat transfer and some basic fluids you would have a leg up on many engineers who never seem to get it (in my design group we used to laugh about those engineers who didn't seem to appreciate the 2nd Law of Thermo when doing heat exchanger design.) I'll take a well informed layman with passion for a subject over a disinterested person supposedly better educated in the subject. You've already got the passion, so do something constructive with it.

I can see the resistance effect in everyday terms when putting a blanket next to an exterior wall, or a pillow on the floor of my uninsulated floor above garage in winter (both surfaces will feel colder beneath than surrounding areas when the pillow is removed.) Same is noticeable at the water heater (hotter) and also on top of my chest freezer when I set something on top (colder.)

Obviously it isn't body heat making it feel colder in the cases with a cold source in previous examples. An average Joe with a good high school/trade education, or years of experience can appreciate that aspect without a fancy/expensive degree.

By the way, the same is true in a scaled water heater. Once the scale exceeds the critical thickness of a few mm's the wall temperatures begin to rise. This isn't a problem for a long time, until the scale is sufficient to overheat the wall to the point of rapid corrosion and/or significantly reduced efficiency. The result is a death spiral. I've seen this same sort of process in various types of process heat transfer equipment and am not bad at figuring out ways to prevent, anticipate, or mitigate it. I've also seen poor pH control eat the magnetite film in a high pressure boiler...the resulting tube failure with black soot mushroom cloud and firebox bricks flying about was exciting, but expensive for the facility. Once I modernized the boiler feedwater control and retrained our operators the longstanding problem didn't reoccur, plus we minimized our blowdown losses. Win-win.

Furthermore, I carried the boiler stoichiometry of this same process over into the refining section of the plant and solved some 40 year old problems with it that escaped some brilliant engineers...including the CEO of my multi-billion dollar employer who had worked on the same projects on the same unit. I'm not necessarily the smartest guy in the room, but I'll catch some things he never noticed...

Patience, Grasshopper...

[Doherty Plumbing]

Wrong. Any time you put significant insulation over a primary source you will find that the temperature between is now closer to the source (in this case the water heater tank.) This is introductory heat transfer. Seriously, all animosity aside, if they offer trades courses in this I think you would both benefit from and enjoy them--plus I think it would help your customers in the long term. You seem to have a strong interest in the subject, and that is a positive thing. If you mastered the fundamentals of heat transfer and some basic fluids you would have a leg up on many engineers who never seem to get it (in my design group we used to laugh about those engineers who didn't seem to appreciate the 2nd Law of Thermo when doing heat exchanger design.) I'll take a well informed layman with passion for a subject over a disinterested person supposedly better educated in the subject. You've already got the passion, so do something constructive with it.

I can see the resistance effect in everyday terms when putting a blanket next to an exterior wall, or a pillow on the floor of my uninsulated floor above garage in winter (both surfaces will feel colder beneath than surrounding areas when the pillow is removed.) Same is noticeable at the water heater (hotter) and also on top of my chest freezer when I set something on top (colder.)

Obviously it isn't body heat making it feel colder in the cases with a cold source in previous examples. An average Joe with a good high school/trade education, or years of experience can appreciate that aspect without a fancy/expensive degree.

By the way, the same is true in a scaled water heater. Once the scale exceeds the critical thickness of a few mm's the wall temperatures begin to rise. This isn't a problem for a long time, until the scale is sufficient to overheat the wall to the point of rapid corrosion and/or significantly reduced efficiency. The result is a death spiral. I've seen this same sort of process in various types of process heat transfer equipment and am not bad at figuring out ways to prevent, anticipate, or mitigate it. I've also seen poor pH control eat the magnetite film in a high pressure boiler...the resulting tube failure with black soot mushroom cloud and firebox bricks flying about was exciting, but expensive for the facility. Once I modernized the boiler feedwater control and retrained our operators the longstanding problem didn't reoccur, plus we minimized our blowdown losses. Win-win.

Furthermore, I carried the boiler stoichiometry of this same process over into the refining section of the plant and solved some 40 year old problems with it that escaped some brilliant engineers...including the CEO of my multi-billion dollar employer who had worked on the same projects on the same unit. I'm not necessarily the smartest guy in the room, but I'll catch some things he never noticed...

Patience, Grasshopper...

I think you fumbled the 1st sentence of what you said so I'm not sure exactly what you're trying to say but if you're telling me that putting insulation over his hand and then placing it on the tank isn't causing his hand to feel warmer (then without insulation) I would ask you if you put a blanket over your body at night when you sleep to keep warm? Do you put your hands in your pockets on a cold day to keep them warm?

Again the 1st sentence didn't make sense but I tried to make sense of what you wrote and I think I know what you're saying.

[Runs with bison]

I think you fumbled the 1st sentence of what you said so I'm not sure exactly what you're trying to say but if you're telling me that putting insulation over his hand and then placing it on the tank isn't causing his hand to feel warmer (then without insulation) I would ask you if you put a blanket over your body at night when you sleep to keep warm? Do you put your hands in your pockets on a cold day to keep them warm?

Again the 1st sentence didn't make sense but I tried to make sense of what you wrote and I think I know what you're saying.

Read it again, pause, relax. It is what I meant. If you put an additional blanket on your bed (insulation) it is to keep you and your hands/feet/etc. below warmer. The space in between the final surface is warmer than before you added the blanket. If you already have two or three blankets of the same type the next blanket will have a diminished effect, but it will still be warmer.

Now consider R8 (1 blanket) vs. R18 (R8 + R10) two blankets. You will not lose nearly as much body heat to the surroundings with two blankets as with one. This is why when I worked in the Alaskan Aleutian Islands I used three layers of clothing for outdoor work 7days/week...and still became hypothermic on some wet 10-12 hr days at 40 F with the wind blowing 30 mph sustained. I was eating about 5,000 calories/day and still having trouble keeping up metabolism wise, but I was strong as an ox.

[Doherty Plumbing]

Read it again, pause, relax. It is what I meant. If you put an additional blanket on your bed (insulation) it is to keep you and your hands/feet/etc. below warmer. The space in between the final surface is warmer than before you added the blanket. If you already have two or three blankets of the same type the next blanket will have a diminished effect, but it will still be warmer.

Now consider R8 (1 blanket) vs. R18 (R8 + R10) two blankets. You will not lose nearly as much body heat to the surroundings with two blankets as with one.

And one sheet of R18 insulation would be equal to the R10+R8 so what's your point?

I know exactly how heat transfer works thank you very much.

Your hand is warmer then the air/objects around you so you're putting out heat because everything wants to be the same temperature.

Now all of a sudden you wrap your hand in an insulator and it's going to get hotter because your body is taking in heat (or generating it) and putting out heat. However your hand now can't lose as much heat as it's taking in so you're hand is going to feel warmer.

So again I would say you couldn't attribute the fact that his hand was heating up under an insulator to the fact that it is primarily because of the heat loss of the tank.

So be patient grasshopper.

[Runs with bison]

Unfortunately, you don't understand or we wouldn't still be discussing this. Calculate wall temps for varioius increments with several R values. Calculate the overall U. Then get back with me.

Alternatively. Do the one blanket, two blanket, three blanket scenario. Put your hands over the first blanket. Tell me which is warmer to you with subsequent blankets: no more, 1 more, 2 more. Or use an infinite case if you like: put on an R8 blanket...then and R100 or R1000. Then repeat with a third blanket. Will your hands be closer to the external ambient? Or to body temperature? I'm not trying to insult you, just trying to convey the core of the lesson. Calculate the wall temps for each layer and the answer is obvious. If you can't calculate wall temps then you don't yet understand the mathematics and theory involved. That's not a dig, just the reality. I don't expect folks to understand this off the bat, but I do expect them to be able to reason through it, given help.

Look up the mathematics of resistances and heat transfer coefficients. These are defined for you, no need to take my word for it. I'm not the originator or gatekeeper of the definitions.

[Doherty Plumbing]

Unfortunately, you don't understand or we wouldn't still be discussing this. Calculate wall temps for varioius increments with several R values. Calculate the overall U. Then get back with me.

Alternatively. Do the one blanket, two blanket, three blanket scenario. Put your hands over the first blanket. Tell me which is warmer to you with subsequent blankets: no more, 1 more, 2 more. Or use an infinite case if you like: put on an R8 blanket...then and R100 or R1000. Then repeat with a third blanket. Will your hands be closer to the external ambient? Or to body temperature? I'm not trying to insult you, just trying to convey the core of the lesson. Calculate the wall temps for each layer and the answer is obvious. If you can't calculate wall temps then you don't yet understand the mathematics and theory involved. That's not a dig, just the reality. I don't expect folks to understand this off the bat, but I do expect them to be able to reason through it, given help.

Look up the mathematics of resistances and heat transfer coefficients. These are defined for you, no need to take my word for it. I'm not the originator or gatekeeper of the definitions.

I was correcting you on implying that R10+R8 is better then R18 insulation. I understand that blankets will reduce heat loss at a reduced rate because of air trapped between each layer acting as more insulation.

So my question to you is what's your point?

Assuming the HWT has R16 insulation (guessing here obv) the tank is only losing about 3 BTU / hr per sq ft of surface area. I don't think this would explain a fairly quick noticeable effect on his hand. But maybe the ~222 BTUs the human body gives off might be a good explanation. But I'm clearly not as smart as you so I wouldn't know.

[nukeman]

There are multiple things going on. I don't trust how thing feel. For instance, your hand exposed on a 30F windy day will feel cold, but not as cold as a wet hand under the same conditions.

Take the garage floor example. Say the whole room is at 60F (including the floor). The floor will feel colder than everything else eventhough everything is at the same temperature. The difference is that the concrete/earth is better at conducting your body heat than wood/drywall in the walls or the air itself. The blanket on the floor isn't really holding body heat in, but limits conduction to the concrete.

A similar thing is that aluminum at 200F will burn you more quickly than ceramic at the same temperature. The aluminum will feel much hotter even if it isn't.

When something feels cold, it is really due to heat loss. That might be really cold air with no wind, little bit warmer air with some wind, or quite a bit warmer air being wet + wind. All these might feel the same even if the temperature is different in all cases. The other aspect is whether the core of your body is cold. As we know, the body cuts blood flow to hands, arms, etc when the core is cold. If you can keep the core warm, your hands will stay warmer. So, take a measurement instead of trusting what it 'feels' like.

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.

[Cass]

To find out the answer as to how much $$$ is saved by insulating a water heater, and that is the whole point of insulating one, there are to many variables to be able to find out the maximum amount of insulation in relation to savings and where that point becomes neglegable...each situation would be different...and it would require measurement instruments that 99.999% of people don't have...

[Ian Gills]

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.

[leeelson]

You were likely just feeling the heat being released by your body getting trapped under the insulation. I wouldn't attribute this to the heat loss of the tank.

You need to use a remote thermometer.

Nope. If I put the insulation next to drywall and stick my hand inside, the temperature feels no different than the it does with the drywall alone. The water heater is definitely loosing heat and its being partially trapped by the insulation.

Maybe the thing missing in the above discussion is that although there is heat generated by my hand when I put it between the insulation and any other surface, it is a relatively small amount, especially in the first 10 seconds. (Perhaps if I left my hand there for an hour, it might feel some accumulated heat). The point is, the water heater definitely looses heat and that heat is partially trapped between its surface and the insulation. How much heat is trapped, what the economics are are another matter.