Choosing an All-Electric Water Heater
Hi,
I am looking for an electric hot water heater for domestic hot water. I understand that there is a balance between the volume (in Gallons) and how quickly the hot water is heated while it is being used.
I am also in an area with very low overnight rates (1/10th of daytime rate) which for me suggests a larger one may be a good idea where at least some volume is heated at low rates. Is there some way to model that?
And if not, what is the run of the mill (reliable, quiet) water heaters out there? Family of 4, with children who think they are fish, so sizeable hot water use for baths and showers. (The one joy in cold climate, so not going to come down too hard on that one). Is 80G big enough?
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Replies
Electric resistance tank heaters are quiet, and bigger would provide more hot water. If you want, you can store the water at a higher temperature and mix it down to 120 with a mixing valve. This has the effect of storing more energy using the same volume. You can model it pretty easily: take the $/kwh off peak and multiply it by the energy you plan to store off peak. For example, if you bring 80 gallons from 120 to 160 overnight, that’s storing (160-120)*8.34*80/3412, you store 7.8kwh.
You may find it benficial here to use several smaller water heaters connected together in series. If, for example, you used two 50 gallon 5kw water heaters, you'd have essentially a 100 gallon 10kw water heater. The two tanks gives you the extra capacity you want, and the double heating capacity allows for more hot water to be made during your cheap power time. To set this up in an optimal way would require some extra logic, with the ideal being two setpoints: one setpoint would be lower temperature, and would trigger at any time of day, the second would be a higher temperature and would only trigger during the cheap power time. This would result in a system that would run less often, maintaining a lower temperature, during times when power was expensive, but would maintain a higher setpoint during the times when power was cheap. This would ensure you'd not run out of hot water during a busy day, but you'd do most of the "work" of heating water during the time of day with the cheaper electric rate.
Bill
That is interesting; thank you.
My difficulty is that I need 2 water heaters - one for in-floor heating which I was going ask about separately - and I have a small-ish mechanical room.
Would your idea of set point temperature be achievable with Paul's suggestion - a larger heater with varied temperatures?
Yes - for example, Rheem's app lets you set different temps for different times. Another option to consider/combine is a drain water heat recovery pipe. It's another way to expand capacity and it saves energy unlike bumping up the water temp.
Thank you.
(DWHR have been discussed already - this is just about the heaters).
+1 On this setup for domestic hot water. You can use a standard water heater timer for the TOD high temp unit. Two smaller tanks will cost less than a big tank.
There are not tank water heaters rated for space heat. If you want floor heat, get an electric boiler. They are way smaller. Even a 120gallon tank doesn't store enough heat overnight to get you through a day of space heat (assuming 40C delta stores 21kWh of heat).
If you want long life water heater go for a stainless tank or one with two anode rods. The life of a water heater is pretty much determined by the anode, as long that is replaced when needed, it will last. Mine is about 20 years old and on its 3rd anode. The hard part is replacing it the first time which is not fun on an old tank, you can simplify this by pulling it when new and re-installing it with teflon tape.
Thank you both very much.
Many municipalities are now requiring hybrid / heat pump water heaters for those going electric. They cost a bit more, but they use half as much electricity.
As for "what is a good one", that's what product reviews are for. You want to look at what hundreds or thousands of customers think about a particular model, not one or two replies you might get on a forum.
Thank you. I am not considering heat pump water heaters for the reasons I do not want to get into. I already have an air to air heat pump.
I find people on this forum far more knowledgeable than the 1,000 reviews on Home Depot.
Even people here who are energy experts can't tell you about statistical failure rates of a particular model based on their experience of owning only one (or installing only a handful as a builder). I use GBA for what it's for, and I use crowdsourced product reviews for what *they're* for.
Product reviews for nearly everything tend to skew towards the negative, because people are more likely to complain about problems than they are to post about good experiences. With DIY installations, you always have to wonder if the purchaser/installer botched the installation, and the failure isn't the fault of the product too.
Basically, I always recommend taking "crowd sourced reviews" with a grain of salt for those reasons.
Bill
Sure, product reviews skew negative, but that's irrelevant to my point, because *all* the products are skewed by the same percentage, and the point is to compare among different models. The one with the lowest percentage of negative reviews is likely the most reliable.
Wondering about installation failure is likewise pointless, because it will also be the same for all models.
I do not know much about water heaters but I do know about product reviews a little.
Expectations differ: people buying premium products expect more from them and those with more experience with luxury goods rate harsher.
So while Maytag and Thermador products may each have 4 stars, the reviews do not mean the same performance.
And I want opinion of those who know Thermadors and Maytags as I want to buy good quality for reasonable price.
The replies I have received here in the past were just the level I needed.
Understand you don't want to consider a HP WH, but just thought I would throw a few things out there:
1. Some on this forum have identified a very quiet Stiebel model, so that alleviates the noise concerns
2. There is a considerable rebate for a HP WH if you are moving from gas. If you already have an electric WH, the economics are less compelling.
3. HP WH's are far less expensive to operate
4. At a recent sustainability workshop they touted not only HP WH's, but also electric point of use. Thinking about this, this does not need two separate electrical feeds. There are devices that will have the power go to one or the other and you can set them up in series. Use the HP WH for most HW use, set it up such that at a large hot water draw, when the leaving temp of the water in the HP WH drops below a preset temp, the power switches over to the inline WH and instantly heats the water. This gives you the advantage of less space used than 2 WH, the inline is only used when the tank starts being depleted so most of your water is heated via the efficient heat pump, it eliminates the concerns about HP recovery times, and the temperature delta the inline WH needs to overcome is less than incoming water because the water is the tank is somewhat warm, so that also works better. It is an interesting approach.
Interesting - I actually went to revisit this and that was the only quiet model (Stiebel Eltron Accelera 300 E) but it seems to have extremely limited availability and the performance is a bit unknown. I couldnot even find a supplier (in Ontario) and it is heavy and large (forklift required to move from what some online retailers claim).
I have a bedroom right next to the mechanical room, so this is the upper limit of DBA I am prepared to consider.
I also have a small mechanical room - just at the min required size for indoor heat pumps by volume.
You can get a 10 year warranty by getting a pro to install a typical electric water heater, it works out to $25ish a month. Pretty minor all things considered.
It occurs that the Rheem Marathon, which as I understand things, has an above average level of insulation. This could be advantageous if one had the plan of heating water overnight for use during the day.
Though the risk is likely low, I am wondering if anyone has looked into the possibility of bacteria growth during the time of day when the water heater is not operating.
Though a heat pump water heater is likely more efficient, it could be argued that there is an advantage to having a Marathon, which has a longer projected lifespan, if I read things correctly the Marathon could outlast a couple of HPW heaters.
Ben
Ben,
Any water heater with a tank should be set up so the water never goes below the temperature necessary to avoid bacterial growth for an extended period. Here it is a building code requirement that it be set up to maintain 60C, but practically that might not be be necessary and short periods when that doesn't occur are fine.
Makes sense. I have often wondered if it is feasible to set up the Rheem Marathon so it only heats water at night, but can do so without growing bacteria by day. If there is a reliable and straightforward solution, I’d be interested.
Though for our project we are lucky enough to be able to orient the building to the sun, and we will hopefully cover nearly the entire roof in solar panels.
Ben
Ben,
I think the usual recommendation is that it reach 60C at least once every 24 hours, so some intermittent off times should be fine. I have amended my first post to reflect that.
A funny, semi-related story:
I did a lot of work for a nearby resort with 25 cabins with hot tubs. One of the neighbours buttonholed me one day and asked if I could trouble shoot his hot tub, as it was the same make. When I lifted the lid, it had about two inches of orange foam on the top. I asked him how much bromine he was using. "What's bromine?" he replied. I asked if he had any skin problems. he opened his shirt and was bright red and blotchy from the shoulders down. He had been using the tub for over six months with no chemicals. He was lucky to be alive.
Speaking as a recovering emergency room RN, I am both shocked and not shocked, in regards to your story.
This actually just came up - the marathon has efficiency ratings lower than other Rheem electric tanks. The consensus is that while it lasts longer, it’s probably not significantly more insulated and may be less insulated. All that said, all new electric tanks have decent insulation and chasing more is probably a waste of money.