Water heater insulation

Runs with Bison · Dec 14, 2009

Doherty Plumbing said:
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 · Dec 14, 2009

Runs with bison said:
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.

Sponsor · 2022-01-29T12:20:58-0800

Runs with Bison · Dec 14, 2009

Doherty Plumbing said:
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 · Dec 14, 2009

Runs with bison said:
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 · Dec 15, 2009

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 · Dec 15, 2009

Runs with bison said:
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 · Dec 15, 2009

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 · Dec 15, 2009

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 · Dec 15, 2009

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 · Dec 15, 2009

Doherty Plumbing said:
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.

Dana · Dec 15, 2009

nukeman said:
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.)

Nukeman · Dec 15, 2009

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.

Runs with Bison · Dec 15, 2009

Doherty Plumbing said:
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.

Runs with Bison · Dec 15, 2009

Ian Gills said:
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.

Runs with Bison · Dec 15, 2009

Dana said:
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.)

nukeman said:
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.

Ian Gills · Dec 16, 2009

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.

Runs with Bison · Dec 16, 2009

Ian Gills said:
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.

Ian Gills · Dec 17, 2009

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.

Dana · Dec 17, 2009

Ian Gills said:
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....

Runs with Bison · Dec 17, 2009

Ian Gills said:
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.)

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