Turning off the hot water heater question

ok, when i was single (used hot water only in the morning to shower and again at night) my bill ran round $38/month...(boy were they the good old days!!!???). i installed a timer with on times just enough to supply needs...my bill dropped to $18.00 per month.

harder to do now, wife wants hot water when she wants hot water.

insulate tank, pipes, turn water temp down to lowest possible, if you can get you household on a schedule you will save....doesn't X10 have some remote control stuff for waterheaters?

i think most studies indicate that the tankless are not money savers unless house has long pipe runs on uninsulated and non looped plumbing. (i think plumbers have forgotten about looped hot water lines) anyway the advantage of tankless is almost instant hot water instead of waiting for non looped hot water..

My dad used to only turn his water heater on for 3 hours a day. His electric bill dropped by $30 a month

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I've done the math on all of this. I'll give a brief summary in a bit, but first-

Circuit breakers. I've heard the "you'll wear out the breaker by using it as a switch" BS for years. If it wears out, it is because it is a cheap breaker. It is common practice in movie theatres that at the end of the night every breaker in the projection booth gets turned off. In a multiplex there can be ten or more breaker boxes, EACH of which contain over twenty breakers. I've been in theatres that are twenty years old or more and still using the original breakers, with those breakers having been flipped twice a day every day for those twenty years. Considering the numbers of theatres and the THOUSANDS of breakers and the number of years in the business, I can say without reservation that flipping breakers has next to no impact on the lifespan. What DOES wear out breakers is a circuit that is overloaded enough that the breaker trips fairly regularly due to an overload condition. That causes the breaker to be operating in an environment where it is extremely hot. If you feel a panel and one or more breakers is actively hot, you have a possible danger that should be investigated.

Water heaters (electric) Consider:
The immersed electric elements are almost exactly 100% efficient at heating the water.
The ONLY savings that you can get are from reducing the wasted heat through the insulation and the pipes, and by reduction in usage.

TURNING A HEATER BELOW 130 DEGREES MAKES IT A BREEDING GROUND FOR SOME BACTERIA, INCLUDING LEGIONNAIRES DISEASE.

Cycling a heater on and off will cause the metal to expand and contract. This puts stress on the welds and may shorten the lifespan of the heater. The effect isn't large in a new heater, but in an older one, where corrosion has already started, it can be an issue.

I did my calculations based on a 40 gallon electric water heater. I make no claims about gas heaters, because I didn't do the calcs on them. To start - for the two of us, measuring our total usage over a period of time, I found we used $1 worth of heated water per day for washing, laundry, showers, etc.. That figure is fairly consistent with the yellow stickers on new heaters. Since it was by actual measurement, it takes into account all losses from "wasted" heat. Total cost of hot water per year - about $365. With me so far?

That figure is with the heater turned to 160 degrees, which is a safe water temperature. Anyone who has worked in the food industry and taken safety courses already knows that food should never be stored between 55 and 155 degrees. Water, unless it is distilled or dosed with chemicals, has bacteria, and water tanks act as settling tanks where masses of the bacteria can live in any organic matter that settles out.

For safety, the safest way to handle heated water is to have it very hot until it gets to the faucet. On mixing faucets, there is an often anti-scald component that can be set to keep the temperature in a safe range. Better yet, there are mixing valves that can be installed before the faucet to lower the temperature just before it hits the tap. Otherwise, a single mixing valve on the output line of the tank keeps the water going to all taps safe, while keeping the water in the tank at a temperature that will inhibit bacteria growth.

Now, on savings. There are three concepts to be aware of.

1. Is the heat really wasted? If you heat with electrical resistance heat (Eden-Pure heater, ceramic electric heater, quartz heater, electric baseboards) and your heater is in the heated area of the house, your "waste" heat goes to heating the house and you save exactly ZERO by fiddling with timers or insulation. In other situations, the heat may be being used to prevent pipes from freezing. Even if you heat by other methods, during the winter, waste heat from the heater is not a 100% loss, but reduces heating costs slightly.

2. Usage. Here is a quicky question - Which uses more energy? A ten minute shower at 100 degrees when the water heater is turned to 120 degrees, or a ten minute shower at 100 degrees when the water heater is turned to 160 degrees?

The answer - they both use exactly the same amount of energy!. When the heater is turned to a lower temperature, the mixer valve at the shower has to mix MORE hot water with the cold water to get the 100 degree desired temperature.

If you do not change your habits of water usage, the only effects of turning your heater down is a reduction in the capacity of how much heated water is available at a set temperature, an increase in the change of harboring bacteria, and a slight reduction in heat lost through the pipes and insulation around the tank.

3. Delta T. Delta T is the difference in temperature between the ambient air temperature and the temperature of the water that has been heated in your tank. Delta for difference, T for temperature. Why is this important? It dictates the effectiveness of insulation.

If you insulate between a pipe carrying 70 degree water and the ambient air, which is 71 degrees, you are wasting your money. The cost of insulation will far outweigh any savings over your lifetime. On the other hand, if you insulate between a tank of water at 160 degrees and a 40 degree crawl space, your insulation will save you a lot of money.

What many people forget is that in a tank that is turned on and off, the water in the lower part of the tank isn't heated at all. Open up the inspection panels and use a non-contact thermometer to prove this to yourself. Water stratifies according to heat. Hot water is less dense and floats towards the top. Cold water sinks.

In ANY electric water heater, insulation below about the lower element point of the tank wall does nothing to save money. Insulation on the TOP of the tank has the greatest effect. HOWEVER, tank manufacturers now insulate tanks better (Federal standards and all that) so that adding insulation to the tank itself is generally not worth the money. Similarly, cutting off the power to any of the newer, better insulated tanks saves little. I did the computations on insulation, usage, and timers and Delta T on the tank in our house in Florida and found that the $40 for a timer box would take over four years to break even in savings. Adding insulation to the tank was even worse, with a payback of six years. Part of this is the simple fact that the insulated surface area of a tank is very small. There is little opportunity for heat to transfer out of the tank compared to the heat in a house transferring out to a freezing day. The tank may have a surface of less than sixteen square feet, whereas even a small house may have over a thousand square feet of walls, and a ceiling of eight hundred or more square feet.

What I found WOULD save money is insulating the first four feet of pipe coming out of the hot pipe from the tank. That water there is the hottest water, and uninsulated pipe is an effective radiator. That much pipe insulation was cheap, and the payback was on the order of four months.

Understand that with a total cost of $365/yr for hot water, the maximum of about 10% savings if the tank and lines were perfectly insulated would be less than $40. The cost of a single doctor visit, due to a waterborne disease would be double that.

If you want to save money on water, there are some easy and inexpensive methods that are far more effective and safe. Invest in a low flow showerhead. Some of them are VERY good. Reach under the kitchen sink and turn the cutoff valve on the hot water line so that the hot water doesn't come rushing out when the tap is on full. Yeah, it'll take a little longer to fill the sink, but on those times when the tap is just running, it'll save money. Take shorter showers. Use cold or cool water in laundry.

The intentions that folks have for saving money on hot water are good, but the physics of the newer water systems are already so good that adding timers or insulation or lowering the temperature of the tank are only minimally effective. In the older systems, yeah, there may have been some savings.

Harry,
Your understanding and mine on the manner a water heater functions differ.
Your statement....."What many people forget is that in a tank that is turned on and off, the water in the lower part of the tank isn't heated at all. Open up the inspection panels and use a non-contact thermometer to prove this to yourself. Water stratifies according to heat. Hot water is less dense and floats towards the top. Cold water sinks."
Yes the water will stratify. The incoming cold water is directed (piped) to the bottom of the heater. However, if the water in the top of the water heater is above the setting for the top thermostat the arrangement of the thermostats will shift the power to the lower unit and heat that water to the lower thermostat setting. The lower heating unit is the primary heater! The upper heating unit is used to temper the outgoing water when the water heater is delivering more hot water than the water heater can provide. When there is no water extracted from the water heater, the water in the lower portion of the water heater will become heated, though not as high a temperature as that in the upper portion of the tank. Insulating the entire tank would have merit. The manner in which the hot water piping exits the water heater and connects to the house plumbing will impact the heat loss. In most instances the hot water piping will rise above the water heater. IMO this is a plumbing short coming. If the hot water lines are plumbed to exit downward the length of the water heater and then distributed, the plumbing will stop the thermal siphoning of the heat from the top of the water heater and the lines are much easier to efficiently insulate. I can go to nearly any hot water heater and place my hand to the discharge pipe when no hot water is being used and the pipe will the hot.

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Agmantoo
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you know you can!

Hey.

I would figure you will blow the fuse once-in-a-while with turning it on and off every day...no biggie, just have some spares.

I also would figure you electric tank heating elements may burn out a little faster with all the heating and cool down cycles they will go thru with turning it off every night.

RF

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Harry, I don't agree with you about hot water temperature being necessary for safety from bacterial contamination. If that were the case, why do millions of people on un-chlorinated well water not get sick from drinking the cold water from their taps that has been sitting in a large pressure tank at room/outside temperature?

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Oh and in regards to the breaker/fuse issue, breakers are rated by the manufacturer for switch duty if they are able to be used routinely as a switch. Usually higher quality breakers will have this rating, for example the Square D QO breakers I have in my home are switch duty rated. So, you should check with the manufacturer of your breakers to see if they are switch duty rated. If you have a fuse, there is no reason that the fuse would blow when the heater was re-connected (there is no high starting current like a motor), but you should not use the fuse itself as a switch, as the contacts in the socket will wear/burn out from the arcing.

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This has been talked about several times. Here's one thread to look at. About half way down on the second page, I did some calculations. If you have an old water heater, then a timer can save you some money.

Turning the heater on and off isn't going to wear it out any faster. With only one cycle a day, it will take many years, if at all.

Michael

cfabe, you are correct on the breaker quality issue, but we found that most suppliers will hedge bets and not own up to the breakers being "switch" rated. I also agree 100% on the fuse issue.

As to why cold water isn't as much an issue with bacteria - a couple of reasons. Bacterial growth is not fast in low temperature water. If there is sufficient flow, the amount of bacteria remains low enough to not be a problem. We all ingest bacteria in water. Our immune systems handle a small amount comfortably. It is only when the levels get to large that it can't cope (although people who live in squalid third world conditions do either develop a stronger system or die). If the water is stagnant and lukewarm, it is much more of an issue because growth is faster. In the past cholera and typhoid and "summer fever" were deadly to a lot of people on home water supplies. One of my grandmothers died from such a situation, as have countless others. It is one of the reasons I use a Berkey and chlorinate the water in our cistern.

Agmantoo, you too are correct (lots of smart folks around here). The upper element is fired first (this gives the "quick recovery" boost that allows electric to compete with gas), then the upper element is powered off and the lower element engaged (this cutting off of the top element also allows a smaller gauge wire and smaller breaker than would otherwise be required) , dip tube, thermal siphoning breaker (can be as simple as an upward pipe out of the tank going into a 180 degree bend that goes back down a few inches. Yep. Good stuff. Insulate that thermal break and you're good to go.

Even when the lower element has finished cooking the water, the very bottom of the tank (below the bottom element) is still cooler than the main tank. There is a little convection current that helps out, and a little radiation from the heated water above, but the top is still where the bulk of the heat pools and heat loss occurs. In a case where the heater is being powered on for only a short period (20 minutes or less) the bottom element likely won't engage at all, so the top will be hot, the bottom half at ambient or incoming temperature. Failure of elements depends on usage patterns. Some folks have the top element burn out first, but most regular users lose the bottom one a little sooner, IIRC.

...which reminds me. When talking insulation, the difference between a tank temp of 160 and 130 compared to the outside temp really is almost insignificant. It is only a drop of 30 degrees behind a layer of insulation. Remember that a lot of the "common knowledge" on the subject got its start in the Jimmy Carter "energy crisis" and has been held on to since then as Gospel, even though insulating techniques have been improved. Even back then, a lot of the exercise was simply hype to make people feel good about doing something to "save" energy.

I already own the timer, got it on clearance for 10$ or so, and I have already insulated the heater and nearby pipes. My heater is located in a cellar with a dirt floor and mud, brick and block walls. The cellar stays between 40 and 70 degrees year round, my gas furnace is located there, maybe that's why its warm. As I think about it now, the heater has its own small fuse box with two big ol' breakers in it. The box is in the cellar. The other breaker connects to the barn 100 feet away and runs an occassional light bulb. The cellar fuse box is connected to the main breaker box, which was completely replaced and updated last year. So I think there would be no overload on the wiring or fuse. So.... I am thinking about throwing the switch in the cellar until I need hot water, which is not often. Thanks for all your help. I am in a serious money crunch right now. There is no where else to cut back so I have to do anything I can. Mary.

artificer - you wrote:

Surface area is about 28 square feet.
R10 for 2" foam insulation, and I guessed at 1" fiberglass, R3 for comparison with older style water heaters.
100 deg F and 140 deg F water temps in a 55 degree basement

Using this information, it takes the following energy to keep the water warm for one day:

100deg 140deg
.89KW-hr 1.7KW-hr 2"foam insulation
3Kw-hr 5.6KW-hr 1" fiberglass insulation

At $0.10/KW-hr, the costs are $.09, $.17, $.30, $.56
Using an average 30 day month, the costs are $2.7, $5.1, $9, $16.8


"Surface area is about 28 square feet.
R10 for 2" foam insulation, and I guessed at 1" fiberglass, R3 for comparison with older style water heaters.
100 deg F and 140 deg F water temps in a 55 degree basement"

Reasonable assumptions, and I was using a 40 gallon heater which gives better results, however your 28 square foot figure is a bit high. Figure roughly 7.5 gal per cubic foot. 50 gallons is therefore under 7 cubic feet. The actual tank itself is what you would measure, not the outer jacket. A tank 18" in diameter and 4 ' high fits the bill. Circumference is 4.75'.
http://www.agraind.com/AGRA_Sales_an...calculator.htm

4.75' around x 4' tall = 19 square feet. The top is less than 2 square feet. 21 square feet total of surface area. We don't count the bottom, since the water there is already cool, and heat rises anyway.

Using the calculator here:
http://www.infinitepower.org/calc_waterheating.htm

Water temp at 120 degrees, 55 degree ambient and incoming temp
at R-16 I get a loss of 87 BTU/hr (Kenmore has a heater like this)
at R-10 I get a loss of 139 BTU/hr
at R-3 I get a loss of 463 BTU/hr

Water temp at 160 degrees, 55 degree ambient and incoming temp
at R-16 I get a loss of 140 BTU/hr
at R-10 I get a loss of 225 BTU/hr
at R-3 I get a loss of 748 BTU/hr



There are 3415 BTUs in a Kilowatt hour. We'll figure 10 cents per kilowatt hour cost.

365 days in a year, 24 hours in a day = 8760 hours in a year.


Water temp at 120 degrees, 55 degree ambient and incoming temp
at R-16 87 x 8760 = 762120 BTUs lost / 3415 = 223 KWH = $22.30
at R-10 139 x 8760 = 1217640 BTUs lost / 3415 = 357 KWH = $35.70
at R-3 463 x 8760 = 4055880 BTUs lost / 3415 = 1188 KWH = $118.80

Water temp at 160 degrees, 55 degree ambient and incoming temp
at R-16 140 x 8760 = 1226400 BTUs lost / 3415 = 359 KWH = $35.90
at R-10 225 x 8760 = 1971000 BTUs lost / 3415 = 577 KWH = $57.70
at R-3 748 x 8760 = 6552480 BTUs lost / 3415 = 1919 KWH = $191.90

The above are the TOTAL losses from the tank through the insulation. Even if perfection was achieved by use of an electric demand heater, or perfect insulation, or by cutting the usage of the tank down, you CANNOT go above those figures as savings in a year. It is physically impossible for that part of the system to get more savings.

In point of fact, those figures are generous, because they do not take stratification or heating times into account, nor do they account for any "waste" heat that actually is used in space heating the house or area. In reality, achieving a savings of HALF those figures by any method is almost miraculous.

So, lets compare. For example, we'll say I have an R-10 50 gal tank in a 55 degree environment.
I want to save money by reducing the tank temp from 160 to 120.
$57.70 - $35.70 = $22.00
I have saved a whopping $22.00 in a YEAR by lowering the tank temp by 40 degrees.

In reality, my tank sits in heated space, the insulation is better, and if I got a savings of $12 per YEAR, I would be amazed.

If you go to the R-3 figures, then yes, there is some savings. In the case of one of those ancient heaters (which is probably full of holes and on the dump by now) you could save money by adding a jacket of R-12 to bring the insulation up to about an R-15 - then the figures for the R-16 would be roughly right.

How about a timer on a tank? At R-10, 120 degrees, savings is going to be on the order of $15 per YEAR in a 55 degree environment, maybe $10 per year in a heated space.

See how it all works? Hype, bright shiny objects, promises of great savings, save the environment. Too much of the radical part of the "green" movement is full of this. If you already have a timer hooked in and you don't mind the inconvenience, it may not be worth it to stop using it. However, the low tank temperatures are still a problem, because of the bacteria and other organism growth.

I have had a timer (first provided by my electric co) on my water heater for 25 years. It was mandatory here in 1984, as we were given a time-of-day meter, you know the kind they NOW say will save energy & the building of power plants etc. They did away with those meters around here by the late 80s, but now they are bringing them back. Anyway, I save money by heating my water on "off" times when my rate is 1/3 of my day rate. We are a family of 4 with a 50 gallon electric heater & rarely run out of water. We have had our temp at 120 for 20 years. I really notice an increase in Kilowatts when I turn the WH more during holidays etc. I can't say what we save, but my father who has oil hotwater uses 500 KW or less in the winter & we use 800-1000. All things being equal, my WH uses a lot of electricity. Our houses are very similar & neither of us use electric for heat. I presently have a "little grey box" that Dh installed after our last electric co timer went. It goes on at 9pm & off at 11pm. I also have it on 6am-7am, but may soon discontinue that, as no one showers here until late in the day & the water stays warm. JMHO

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Cindy in PA

Hey.

As Professor Harry pointed out, not much savings in the water heating department.

She has a gas furnace...maybe she should look to cut her heating bill by burning wood.

RF

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Didn't know you could burn wood in a propane furnace. Just kidding of course!

So, my original recomendation was that if you have a newer high efficiency heater, a timer probably doesn't pay. If the heater is in a heated space, it maybe doesn't pay. You can add insulation, and it doesn't pay. Where's the hype? If you have an old fiberglass insulated water heater, and YES, they are still out there, and its in a basement in a cold climate, then the timer can save money.

You apparently don't have any of this, so a timer doesn't make any sense.

You have everything that they recommend for high efficiency, and apparently short runs of piping. Why is it hype if it doesn't work for you? $73.10 in yearly savings, just by lowing the temp? (you use your situation, I'll use mine)

Yes, we should invest $450 to replace our 15 year old water heater. I can't afford it. Probably a lot of people like me out there. For the OP, they have the timer. They only use hot water in the evenings. Their cost is going to be minimal for an immediate savings. Why is this hype?

Once again, this comes down to regional differences. Up here in the midwest, many/most people have unheated basements where the mechanicals are located. Any heat in out 1895 house's basement is wasted. We could re-plumb the house, but its not going to happen

Michael

Michael, relax. I go through the exercise because millions of people have unrealistic expectations and have been led down a primrose path. In the pursuit of pennies, they spend hundreds and thousands, and make life harder than it needs to be. You did some very good work in guesstimating and came pretty close on without anyone guiding you. I honor that you did this and that you weren't taken in totally by the hype.

Yes, I have everything recommended for high efficiency. We only use about 500 gallons of water per week (total) with no attempts at conservation. We came out of Florida paying $100/month water bills and some significantly high electric bills. I knew that since we were going into a new situation, paying a bit more for high efficiency washers and paying attention to the system was something that would pay off for us over time, even though we have our own water and septic. I make no bones about being proud of putting a lot of time and effort into trying to cut ongoing costs.

I'm also not trying to get on the OP's case. There was a legit question asked, and it happens to be a subject that I have researched a lot, for reasons of my own. The "hype" is not coming from you or the OP. It comes from power companies in their little fliers that accompany bills, it comes from "green" groups, it comes from municipalities. In most cases, it is an innocent but ignorant retelling of something that made some sense years ago, but makes much less sense now, especially considering the swine flu hoopla and possibilities.

I absolutely stand by what I said (and what the government agencies also say) that lowering the temperature of a water heater to less than 130 is an invitation to the growth of Legionnaires and other organisms. I absolutely stand by what I said that the cost of ONE illness and ONE doctor visit is more than the amount you might save in a year. I consider anyone who lowers the temperature of their water heater into the dangerous range to be penny wise and pound foolish. Add the insulating blanket to get the R value up to around R-16, and at least run the tank at 130. You'll not have to replace the old tank, and you'll save money. I'm uncomfortable running mine at lower than 160 but whatever.