Could raising a water heater's temperature reduce power consumption?

For years we had merely warm or very warm, definitely not scalding hot, water coming from our faucets and showerheads. Our hot water supply barely sufficed for two hot showers, or one long hot one, or anything combined with a dishwasher cycle.

So I finally got around to raising the temperature setting on our electric water heater, one of those typical 40-gallon tanks, from roughly 120 degrees to 130.

I know it seems counterintuitive, but is it possible that we are saving energy by virtue of not draining the tank of hot water?

Does it take more energy to repeatedly heat a full tank of cold water to 120 degrees than it does to heat, say, half a tank to 130, especially if the “starting” temperature is around 100?

(I’m only guessing at that half-tank estimate, so lets see… That’s like heating 40 gallons from 70 to 120, versus heating 20 gallons from 100 to 130, then of course maintaining those respective temperatures.)

I’m guessing that the difference in energy consumption is insignificant, but is it possible that a higher temperature is more energy efficient with moderate or heavy daily use?

Either way, our new hot and steamy lifestyle has been wonderful. Even our dishes come out cleaner.

If you actually noticed a difference on your energy bill, I’d suggest it’s more likely that it’s because it’s your May bill and it’s (depending on your location) that twilight time between spring and summer where most people aren’t running the furnace anymore and haven’t turned on the AC yet (and least not for more then an hour or two here and there). Those are the two things that really make the noticeable differences in your bill.
Sure, you can turn lights off when you leave the room, make sure the dishwasher is full before you run it, start turning off your desktop that you only use once a week because everyone has tablets and iphones and you might save a few dollars a month and sure, that adds up over the course of a year. But, go a month with AC and watch your bill damn near get cut in half.

If there’s something unusual about the consumers of your hot water (people or devices) that makes them satisfied with a far lower volume of 130-degree water vs. 120, then this could result in some energy savings.

But the basic answer is no. The energy losses from an imperfectly insulated tank and from the pipes when hot water is flowing are closely related to the temperature difference between the water and ambient air. As this difference is greater when the water is 10 degrees hotter, the losses are greater too.

water that hot is a scalding hazard.

insulation blankets around the tank and around the hot pipes are a good investment.

run the dishwasher when other hot water uses don’t occur and turn on sink hot water tap until hot before turning dishwasher on. you will get a better wash.

If you’re an infant, elderly, infirm, or really uncoordinated.

We’re in southern Florida, and, yes, our electric bill is heavily dependent on AC use. Compared with May of last year, our consumption is over ten percent less, but this May was mild (don’t remember if last May was a scorcher) and we were gone for a week with the AC thermostat set high.

I think the difference must be too small to use the electric bill as a gauge. I wonder what the theoretical thermodynamic difference would be.

I think the idea is that we need to use less from the hot water tank to take a comfortably hot shower when the heater is set to a higher temperature.

It’s easy enough to figure out. They make monitors that you can keep an eye on. With this application, you’ll have to get the ones that clamp on to the wires in the breaker box (220, two wires/two clamps). The ones I’ve seen then send the signal back to a monitoring station and then usually from there you send the reports to a computer to look at. I’d leave it at one temp for, say, two weeks and then the other temp for two weeks.

Of course, if you spend more then $50 on this project, it’s going to take a long time to pay for itself. But, then, you’ll have the stuff to measure other things.

Hot water heaters are pretty well insulated, and if you have check valves on the inlet and outlet losses are pretty low. But if you’re heater has to cycle more than once during any period where it’s not being used, like overnight, then you’ll be wasting electricity on heat you won’t use.

Yes but it will more likely cycle twice at night the higher you set the temperature. The hot water will lose heat faster the bigger is the difference between its temperature and the ambient temperature.

Right - but presumably you’re interested in a certain temperature for the water that emerges from the shower head.

This is the result of diluting the hot water with an appropriate amount of cold. You won’t save energy by the scheme of using a bit less hotter water diluted with a bit more cold.

That’s probably true. At least it sounds like it should be true, but it brings me back to my original question.

Imagine a volume of water brought to its boiling point in an imperfectly but well insulated vessel on the stove top, from which I ladle only half the volume to dilute with cold water from the tap to achieve the perfect temperature for some mysterious experiment I’m conducting every day right there in my kitchen laboratory. I then top off said vessel with cold water for the next day’s trial, and it comes up to temperature in a short time.

Now imagine the same volume of water is brought to perfect working temperature instead, so I need to use all of it, after which I have to heat the entire batch from a cold start every day. Will that take more energy?

I’m failing miserably at expressing this process in mathematical terms (or even metaphorical ones), and I don’t miss the days of joules and specific heat one bit, and all the fabulous benefits of hotter water in the house aside, this is at least a “fun” question to ponder.

Oh, and please disregard the notion that my vessel is a good thermal insulator as well as a good conductor. It’s a magic vessel, I believe.

The end result here is that you want to produce a certain volume of water with a certain amount of heat in it. You can do it two ways. You can add more heat to your temporary storage, and mix a smaller proportion of your heated water with the cold water, or you can add less heat to your temporary storage and mix it with less cold water. In the end, you end up with the same amount of water and the same amount of heat either way. So, if everything were perfect insulators, you would break even either way.

But your hot water tank isn’t a perfect insulator. Some heat will transfer to the environment around it. The greater the heat difference between the tank and its surroundings, the more heat will be lost to the environment. So in that respect, cooler hot water is more efficient since it loses less waste heat.

You’ll lose money with a hotter hot water tank.

engineer_comp_geek said what I was going to say. I’ll just add, in case it wasn’t clear from his/her post, that the temperature of a given volume of water is directly related to the amount of thermal energy it contains; so to get a given volume of water at a given temperature, there’s a fixed amount of energy that you need to add to it. So if the net result you want is to heat 10 liters of water from 10°C to 40°C to wash the dishes, you’ll need 1.26 MJ of energy to do it. Turning up your hot water heater just “concentrates” this thermal energy in a smaller volume of water, and then you “dilute” it by mixing it with cold water.

I only shower at my small house and use it as a workshop so hot water for showers and a few dishes is all I use. I turned it down several years ago to where I use no cold water when I shower, My allready small bill went down a bit more.

Go put your hand on the outside o the hot water tank. If it’s like mine, there is not a significant amount of heat, even though the water temp is 135. So how much ehat are you really losing from the tank itself?

The worst offender, as mentioned, is the piping. You have to run the hot water for 10 to 30 seconds (or more) to get hot from the tank to the tap, then you leave that much hot water to cool off in the line. The hotter the water the more energy you waste.

Unless you do all your hot wet work at the same time, thee’s no way around this, other than the major surgery of moving the hot water tank much closer to the kitchen and bathtub (and laundry). In my house, it’s about as far as it can get from some bathrooms, so I waste a lot.

The problem is - if you don’t heat the water, you save a lot. The hotter it is, th more energy you waste - but in the grand scheme of things, it’s not a lot. The pipe loss probably is about 1/20 or less of a full tub, 1/5 or less of a full kitchen sink. You are paying for your creature comforts.

You could probably save a lot more money with judicous use of the hot water. Don’t use hot to wash your hands, if it means wasting 30 seconds of water for a 15 second handwash. (Or washing in lukewarm then finishing by the time it gets hot.) Don’t leave the hot water running higher volume for shaving… fill a sink and turn it off, or use a trickle. have baths together or one after the other while the pipes are still hot. Etc.

A while back, my wife tried turning our hot water up to an insanely hot temperature (160 degrees, the highest it would go, which said it would cause 2nd- or 3rd-degree burns from just half a second of exposure) on the theory that 40 gallons of extremely hot water would result in more of us being able to take hot showers before the hot water ran out, even if t did waste energy.

It turned out to be too scary to leave it that hot, but I’ve wondered if it would have worked. It seems like it should work to me, but was there something we were missing?

A Chinese restaurant I like has a sign by the mensroom sink that says, “Hot Water Very Hot”.

The first time I used the water I chuckled, then let out a little scream. VERY hot indeed!! You could hard-boil eggs with water from the hot tap.

Some of your skin?

Basically, hot water has caloric content - IIRC, X calories raises a 1cc of water 1C degree; the more calories in the water, the hotter it is. Mix hotter water and cold water, you get hotter mix or use less hot water to get the same effect. SO yes, your wife was right. You can get more or longer showers, etc. for the same tank size. It’s just risky to have that option as full “hot” from your taps. I know I occasionally run my hand under the full hot stream by accident.

Odd, I think my tank only goes up to 140. That cn be painful.

I think this is a bad way to assess heat loss. A water heater doesn’t have to be 100 degrees on the outside to be wasting enormous amounts of energy. All it takes is a small differential - five or ten degrees between the surrounding air and the tank. Your hand can’t effectively measure that kind of temperature difference between air and a metal surface. A tank at 65F will still feel cool to the touch, but if it’s located in a garage with air at 55F, we’re talking about a lot of energy lost to the environment.