Actual cost of doing wash loads at high temps w/ internal heater

liriodendronNovember 9, 2011

OK, I have wanted this info for years and only recently my DH has been able to capture it, precisely.

Here's the set-up: I use a varied group of Asko and Miele machines (all the older, somewhat smaller, true horizontal axis, "Euro" designs). They are fed ONLY cold water so no additional heat energy (i.e. not coming from machines' own internal heaters) is used at any point during the cycle. My machines live in the unheated basement of a northern NY house; my tap water temp is generally about 50F as it flows into the machine. I fill the machines pretty full - it kills me to do small, ad hoc loads! All my machines are long-cycle default models (though I have shorter, optional cycles, too.)

Almost all of my loads use warm to hot to darn near boiling temps where possible. Only very delicate fabrics get tap cold or even cool. My basic wash temp is @140F; sturdy fabrics and farm clothes get @155F; bed linens, kitchen linens, cleaning cloths and pet bedding are routinely washed at 190F (or higher if in the Asko).

But I have always wondered how much energy these wash temp choices require and whther it's costing me a fortune. And I've wondered what the additional incremental cost of a 190F wash vs 140F wash.

Now I know, although I am just beginning to collect the data, so this is just the results from the first three loads.

Load # 1) One all-white load of cleaning towels used to help my clean my SIL's new apartment. Four dozen 14" sq. terry towels (aka terry shop rags) that were used with my LadyBug steamer for cleaning walls and particularly grimy kitchen floors and walls and two dozen birdseye diapers (not prefolds) used for cleaning cabinets, bath fixtures, appliances and general dusting.

Miele 1918, 1 Tablespoon Cheer powder and 1/2 teaspoon STTP, no other additive or f/s. Normal cotton cycle, no pre-wash, no added rinse or high water level selected; temp 190F; predicted running time 1 hr 47 min, actual running time 2 hrs, 6 min. Total energy cost of the cycle (excluding energy to pump water from the well): 33 cents.

Loads #2 & #3: Both well-filled (drum full to top, and weighing at least 12 lbs each) loads of mixed colored items: jeans, flannel shirts, cottton turtlenecks, fleece tops, underwear, socks and bath towel and wash cloth. One tablespoon of Cheer each, nothing else. Both cycles done on the permanent press cycle (higher wash water level, fewer rinses -two not four as in above load - and extra fill for post-wash cool down built into program, somewhat lower-power 1000 rpm, vs 1600 rpm spin on the first load) PLUS additional "starch" cycle basically a separate, added full, cold fill, short agitation, drain and high-speed spin that I use when I want to add an additional rinse to the pre-programmed permanent press choices and include a high-speed spin for max water extraction. Temp chosen: the max for permanent press on Miele - 140F. Energy cost averaged over two back-to-back cycles: 25.5 cents per load. Predicted run time: 1 hr 7 minutes, actual (averaged) 1 hr 22 min.

My local cost for electricty is 15 cents per KWH.

I find it very interesting that the higher temp loads cost so little additional to do. I was astounded at the current the Miele motors drew (and did so more or less throughout the long cycles vs the relatively shorter time the hefty heaters were running.)

I have long wanted to know this info and, of course, since these are 220V machines my Killawatt device couldn't tell me. We are in the process of designing a new PV system, so my D(evice geek)H finally convinced me that we should buy a more sophisticated energy monitoring system, and this is the result. I can gather more data now than even I will want.

Next up: cost of 15 min, low-heat, quick spin in my Asko condenser dryer before hanging out (for fluffing and de-wrinkling purposes). Plus sooner or later I'll have a blizzard, or something, and I'll need to do one of my exremely rare full drying cycles. Can't wait to see what cost I avoid by hanging 99.9% of my loads out, year-round.

YMMV, naturally.


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Interesting, but I think maybe the more pertinent question might be what is the cost difference between just letting the hot water come into the washer tub from your hot water heater at what ever it is set at (ours is 125) for a regular "Hot Water Wash" or even 140 degrees if that is what your hot water heater is set at.
As opposed to having it come in cold/warm and then heated up with the internal heater on the washer instead of your hot water heater.

It has always seemed to me that it must cost more to heat up water with the washer than with your hot water heater.

I am sure the difference is very dependent on what kind of hot water heater you have and where it is located but it seems as though a water heater "should" be more efficient at doing its one and only job than an internal heater in a washing machine.
I wonder if the only reason manufacturers don't have HE machines fill washers with hot water from your water heater is because of some loop hole in the Energy Star requirement?

Except of course for temps as high as you are using which is effectively boiling your clothes and would only be achieved by an internal heater in the washing machine.
But I don't think most people particularly need nor would want to wash their clothes at 190 degrees.

But it would still seem more efficient to start with 125+ degree water then heat it up to 150-190.

Then again maybe not, I am sure they have their reasons I just hope it is not to fulfill some loophole in the requirements as opposed to what would actually work better.

    Bookmark   November 9, 2011 at 8:39AM
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I find it very interesting that the higher temp loads cost so little additional to do. I was astounded at the current the Miele motors drew (and did so more or less throughout the long cycles vs the relatively shorter time the hefty heaters were running.)

I'm very interested in this very same idea, as I have a washer with internal heater and am working to lower our electric bills...

. . . forgive me, it's early in the morning, and maybe my brain isn't working at full speed yet, but how much energy did your machine's motors alone draw during your experiments? I didn't see that in your post. I'm very curious to know for my own situation.


    Bookmark   November 9, 2011 at 8:52AM
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"But it would still seem more efficient to start with 125+ degree water then heat it up to 150-190"

Starting with cold water and gradually heating heat gives you a true "profile wash".

    Bookmark   November 9, 2011 at 9:54AM
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Nunyabiz1, the cost of heating the quantity of water used in the washer is essentially the same whether it's heated in the machine or in a household water heater (other than the difference between gas and electricity if the household water heater is gas, and the washer's onboard water heater is of course electric). Heating water involves adding a specific amount of heat energy to it (measured in BTUs) to increase the heat content of the water from the starting temp to the target temp. Doesn't matter how or where the heating is done, the amount of heat energy needed is the same.

The trick to keep in mind is that the household water heater is heating (and keeping heated) a much larger quantity of water than the washer needs. Yes, one can argue that the water in the tank has *already* been heated so one may as well use it ... but of course drawing water out of the tank feeds cold water in that must be reheated to tank temperature. If no hot water yet existed, it's more efficient to heat ONLY the quantity of water that the washer needs, IN the washer, so look at the entire situation from that point of view.

The same thing has been argued in regards to onboard water heating in dishwashers. I have a tankless water heater that can be set to 50F, which essentially turns it off, so I can run my dishwasher on a cold fill. My dishwasher has an internal water heater, and *always* heats the water to specific target temps for the main wash and final rinse per the selected cycle. I have a Kill-a-Watt meter, have checked the electric consumption on a tap-cold fill, and the power usage is quite reasonable -- for example 0.68 KWH (which is $0.102 at $0.15/KWH) heating to a 150F main wash and 163F final rinse on the most intense cycle.

    Bookmark   November 9, 2011 at 11:17AM
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That makes sense, thanks

    Bookmark   November 9, 2011 at 12:14PM
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But it would still seem more efficient to start with 125+ degree water then heat it up to 150-190.
Then again maybe not

The answer may be more complex than you imagined.

Here is a link that might be useful: Mpemba effect

    Bookmark   November 9, 2011 at 1:45PM
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Good morning,

I knew there would be people who were as obssessed as I am with this data!

To respond to the questions (in no particular order):

Yes, my DH reports that we will be able to break out the machines' components (motors vs heater) individual electrical draws. My machines have at least two motors: drain pump and drum rotator/spin. It was easy to see them in the graph as it was happening, but we will need more experience to be able to accurately capture all the data.

As far as the efficiency of energy used by an internal heater vs a DHW appliance, Dadoes is correct. It's a theoretical wash (LOL!). Our DHW is electric, not propane, so fuel is identical. There is also no loss of temp in the pipes (though that heat wouldn't be wasted as it's under the house, anyway). In theory, allowing for age and any scale on the calrods, it should take precisely the same energy in both appliances.

Functionally as livebetter pointed out, however, beefy internal heaters fed only cold water provide the very-useful "profile wash" characteristic. (Profile washes are a deliberate stepped rise in temps that improves washing perferformance.) In addition, an on-board heater also allows the machine to maintain the desired temp throughout the whole wash phase, which I believe improves washing performance as well.

As far as loopholes in the mandated energy ratings, I believe that may be at play these days, particularly for the newest generations of machines (mine are 15-19 years old). However I think heating water is less of an issue there than overall water use requirements.

Nunyabiz noted my use of high temps as being atypical. I agree, but point out that I also use very little detergent compared to many. That's obviously a function of my good water quality, but I also can get away with using less partly because I use higher temps because temperature, time, agitation energy and detergent are all wrapped up together in the cleaning equation. Of course, I almost never wash clothes at 190F, just linens, cleaning cloths and pet bedding which can stand it. In addition to the profound cleaning these items get, the regular use of higher temps keeps my washer clean of bio-film and product build-up, etc. No small thing for FLs, it seems.

(Overnight, I did another load similar to #2 & 3 and it's energy cost was 22 cents. But that's without the extra "starch" cycle which has to be selected manually after the progam is finished. I will check and see what it costs, all by itself.)

It seems to me that heating the water, particularly for people who choose more "more normal" max temps, is not the cost driver on each load.

My DH reports the machine's vampire load is a stable 3 watts; let's see, 3 x 24 x 365 = 26 KWH/year or $3.90 year. Except I have more than one washing machine .... Anyway, now that I know that, a big ole circuit-opening switch will be high on my DH's honey-do list.

More data (and more details) as I organize them.


    Bookmark   November 9, 2011 at 1:49PM
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"In addition, an on-board heater also allows the machine to maintain the desired temp throughout the whole wash phase, which I believe improves washing performance as well"

I would agree with this statement. One of the reasons I chose the Miele W4842 over my LG choice. Only Miele guarantees the temp though the entire wash cycle.

    Bookmark   November 9, 2011 at 4:12PM
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There is an other reason to start with cold water in the wash then let the washer heat it. Stain setting. You are less likely to set a stain starting with cold water in the washer and heating it, instead of starting with hot water right off. It's called a profile wash and it's the reason that it's preferred if you have a washer that can do it.

The amount of energy that it takes to raise water temp by a certain amount is the same regardless of whether it takes place in a washer or the hot water heater.

    Bookmark   November 11, 2011 at 3:29PM
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@ livebetter

You said "Only Miele guarantees the temp though the entire wash cycle." Unless I'm mistaken, I don't believe this is the case. I don't see anywhere on Miele's web site, in their marketing materials, or in the user manual where Miele makes any such guarantee. Can you tell me where you see this?

    Bookmark   November 12, 2011 at 11:48AM
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@sshrivastava, I believe I was told this by the Miele Gallery. I did a quick search for something concrete and I came up with a few things.

The machines are (apparently) tripped out with sensors and sense all kinds of things (including the temp). They are supposed to maintain the temp selected.

"Miele washing machines are equipped with internal heating elements that can raise the water temperature extremely high. Temperatures are based on the program selected and are maintained throughout the washing period."

"Microprocessor adjusts washing and drying conditions to best care for specific types of fabric, including cycle duration, temperature, and spin speed."

"It all starts with the brain of the machine, called Novotronic, which is Miele's surface mounted design (SMD) microprocessor. Novotronic continuously monitors and controls all activity in the machine ..."

"Every Miele washing machine is equipped with DualTherm internal heating elements. These elements allow the water to be heated to high temperatures, regardless of the intake water temperature. This, together with the wash action of Novotronics, means you can do away with using harsh chemical additives ..."

That's all I have time for now. If I find something more concrete, I'll post it.

    Bookmark   November 12, 2011 at 12:29PM
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