Feedback on Sense newsletter Water Heater article

Regarding this article:

I do think it is important to talk about the energy consumption of water heaters, but there’s quite a few things missing from this article and the embedded video.

First, I believe you should add a sentence explaining that a ‘hybrid water heater’ is actually a fully electric heat pump plus a conventional electric water heater. The term ‘hybrid’ is most commonly associated with cars, specifically a hybrid of gasoline and electric. So the natural assumption is that a hybrid water heater would be a hybrid of natural gas and electric. This is not the case, and bears explaining.

Second, there’s no mention in the article of pure heat pump water heaters (not the hybrid type), which for many people, especially those in warmer climates, are a better choice and use less energy overall, and are typically cheaper too. For example, a ducted heat pump water heater can pull hot air from the attic and use it to heat water, then vent cool air into the house. For someone living in a hot climate, this is ideal, as it will greatly reduce both your water heating and space cooling energy use and expense.

Third, unless you have a very long run from the heater to your shower, you can probably set your water heater much lower than 120 deg F. I keep mine set to around 107 in the summer and 110 in the winter. Pipe length is relatively short, takes about 30 sec to push all of the cold water out of the pipes before pure hot starts to flow.

Finally, you mention dishwashers, but most dishwashers are plumbed to hot water directly (at least in the US), so there’s no option to use cold water. I find this very stupid, as I don’t know of any reason to wash dishes in hot water. I’m considering re-plumbing mine to the cold water tap instead. Anyone else done this with success? I’ve lived in other countries where dishes are only cleaned with cold water and it isn’t a problem, though those were all warmer weather tropical places, so the water supply temp was probably a bit higher.


If the dishwasher has a heating element that cannot be disabled, then plumbing it to the cold water would be a waste.

I would like to see a quality cold water dishwasher. We added two people recently and now run it daily. If it works as well as the hot versions then I would give it a go. You may need to leave it a while, before emptying, so that the dishes can dry.

We probably use the clothes washer on warm or hot too often also. It is simple to save energy, however,I don’t know many people that do this.

My dishwasher (Asko D3112 which we bought used) has the ability to disable the internal heating element, which is great. That’s what we do, so our dishes currently get washed in ~105 F water. There’s no heating element used for drying in my model, so to dry the dishes we just open the door and let it air out for a few hours. Works well enough, even though it is somewhat humid here in Oregon. I’m sure there are many dishwashers that don’t have the option to disable the heating elements. I agree that if you already have an efficient water heater, that is likely much better than using a dishwasher’s internal resistance heating element, which would have to work very hard to heat cold (45-55 F) water to 120 F. We also run about one load per day, we aim for the middle of the day to make the most of solar.

For clothes, we wash pretty much everything on purely cold water, and I think all clothes washers have that option. We use cloth diapers, so for that sometimes we’ll use warm or hot, but not every time. Hang drying clothes on a sunny day saves a ton of energy, and for diapers the UV actually helps to sanitize them and sun-bleaches them back to white. On rainy days we’ll still try to hang dry indoors, but we do still use our dryer sometimes. We’ve found that hang drying for a day, then running the clothes through an air-only dryer cycle (ours is labeled as ‘air only - no heat’ on the temp dial) is a good hybrid solution, since you never use the dryer’s heating element, and but you still get nice soft tumble-dried clothes. Running the drying in an air-only cycle is very energy efficient, ours only consumes a few hundred watts, compared to about 5kw when the heating element is running.

I just learned of the existence of heat pump clothes dryers! So I’ll definitely be looking into those in the near future. Should be a huge energy saver.

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Turn your water heater temperature to 120F or above right now!

I don’t want to sound alarmist but there are very good reasons that 120F is the national minimum temp., namely: Bacterial growth avoidance

In addition, that is the minimum supply temperature, which in a normal gas water heater setup would be supplied by mixing down even hotter water (150F+) to 120F. The recommended minimum for an electric tank is actually 124F but 120F is considered the standard “safe” minimum. [Plumbers/electricians feel free to weigh in]

I suggest this while being painfully aware that it would be great to just turn the temperature down to save energy. Really really, don’t do it.

[As an aside I know the guy who was responsible for making the world aware of Legionnaires Disease]


I plan on installing a Miele heat-pump dryer at some point … the main issue I have in my way-too-complicated space (in NYC) is the controlled venting of that and a potential hybrid water tank in summer/winter. In a small apartment the heat-sucking action becomes a major factor. Great in summer, far less than great in winter.

You may have seen this other post. My energy anxiety is really compounded when seeing how they do things in Switzerland & Germany. Why can’t my fridge heat my water!

Thank you for bringing up the bacterial safety aspect! I hadn’t really considered that. I don’t claim any expertise about that, but in my initial research I’m seeing stuff that supports what you are saying, such as this article:

Everything I’ve found thus far has to do with tank style water heaters, saying that the lower 95-115 F temps at the bottom of the tank promote bacterial growth. My water heater is tankless (a.k.a. on demand, specifically I have the EcoSmart Eco 27, which was very cheap to buy but rather expensive to install). Do you know if these concerns apply to tankless systems as well? Even when I’m running my water heater at a lower temp, there’s never a time where water is stagnant and sitting at a lower temp, it is always flowing and either being actively heated (during the shower) or passively cooled (in the pipes after the shower).

AH OK! Good. Didn’t realize you had tankless on-demand!

Usually you need to run the (sitting) water for a little and wait for the heat so you are safe from bacterial hell I believe, especially with short pipes. Whew. In your case the lower temp is fine. Actually makes me realize that in general unless a tank is really well insulated and/or heat-pump powered … unless you have solar … a tankless system also has that advantage: that you can run it at a lower temperature!

I believe though, all things considered, that instant-heat systems (tankless electric) will become a thing of the past eventually because of the advantages of using a large-tank thermal mass as an energy battery. Water tanks are going to get much bigger I believe in temperate climates. In high-solar locations I can see the possibility for tankless water heaters … tanks of cold water will be OUTSIDE and really big. Gotta drink! (Australia anyone?)

I have serious doubts that a standard dishwasher would produce acceptable cleaning results with cold water and no internal heating. Cold water and granulated detergent is a nonstarter, and even with liquid detergent, I don’t think cold water would break down fats and food residue enough to get them off the dishes, let alone down the drain.

Legionaires disease

120 is dangerous.
Take a look at all the veterans that died due to this at an Ohio VA

Sense found my tank type electric water heater quite easily. Prior to installing Sense, I had installed an “Aquanta retrofittable water heater controller” to make my dumb water heater a smart water heater. Sense helped confirm how the Aquanta controller is optimizing the water heater energy use. Check it out at
Also, works with Nest (think Nest Away), hopefully Google will also pick it up. Most days the water heater only runs once a day, laundry day or visiting guests the exception, for a family of (2).