Hot water heater
I am looking to replace my gas water heater with an electric version, but I am rather confused on the best option.
I am deciding between the eco2 / sanco2, a hybrid (like Rheem or Bradford and white), and an on demand system.
Sanco2
This seems to be the most efficient, but it is expensive and bit difficult for me to fit the outside unit. Cost, however, is not the biggest concern for me.
Hybrid
This seems like a good option, but I am concerned about noise on many models. I also would be putting this in my unfinished basement. I have read some posts about it not being advisable to move/disturb basement air, but I am not really sure I understand the concern. I potentially could vent the exhaust out, but not the intake, which I assume would cause the air movement problems. Also, to vent the exhaust I would need to place the unit much farther from the hot water faucets.
on demand
I plan to eventually install solar panels and a battery system. I read that these systems pull too much energy at once to be used with solar. I was looking at the stiebel eltron system. I would really prefer an on demand as I live in a small home and getting space back in the basement would be great. However, I am curious about the downsides.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I installed a Rheem hybrid in the basement of a house I rent to one of my kids. He and his partner have had it for two years and have been very happy with it. They haven't found the noise annoying and as a side benefit have been able to unplug the dehumidifier they used to run in the basement.
On demand has the size benefit. Downsides are inefficiency and the “on-demand” nature of it - it can provide a certain GPM and nothing more. A tank, since it has a buffer, can exceed the flow of an on demand for short periods. Imagine you’re taking a shower and washing clothes- you might be using 2 GPM for the shower, which fits a tankless. But if the washer calls for hot water, you could quickly exceed the maximum output and end up with a cold shower.
Thanks. I am trying to better understand the efficiency differences. We only have one bathroom (possibly two in the future). I don’t think we have high demand, so I do wonder how much efficiency is lost with water sitting in a tank.
With electric, the big difference is that you can't use a heat pump with on-demand, it doesn't have the instantaneous capacity, you have to use resistive heating. Heat pump is 3 to 4 times more efficient than resistive heating.
ecosesne25,
" ...how much efficiency is lost with water sitting in a tank? "
- During the heating season none, as losses are contributing to space heating.
- It depends on the heater. With a well insulated tank, like a Rheem Marathon, the losses are tiny. There may be losses in the lines though.
"- During the heating season none, as losses are contributing to space heating."
Good point!
Yes, so long as the tank is in the conditioned space. In this case the unfinished basement would need to be in the conditioned space.
The home is over 200 years old. There are no vents in the basement. It’s directly below a conditioned space, but I’m not sure I would classify it as conditioned from what I have read. It certainly impacts the first floor as the ground heat moderates the temperature on the first floor all year.
Tankless is the same efficiency (or extremely close) as a resistance tank, so 25% as efficient as a heat pump. Not having a tank doesn’t gain you much efficiency.
"I read that these systems pull too much energy at once to be used with solar. "
Not my area of expertise so someone please correct me if I'm wrong. It's my understanding that if you have a grid tied PV system, and assuming of course that the wiring to your electric on demand unit is properly sized, there will be no problems with solar.
Jolly,
That's correct. But the original question is ambiguous. EcoSense wrote, "I plan to eventually install solar panels and a battery system." If EcoSense wants to cut the cord and live off-grid, an electric water heater won't work. A solar thermal system would make more sense for an off-grid house.
Thanks. When I looked into solar, I was informed that if the grid went down, my power would be down too. One of the reasons to go solar was to maintain power during outages. I don’t have enough capacity, however, to go off grid for extended periods at full usage. I will need some power from the utility. The battery is really only to provide minimal electricity in emergency situations. I could live without hot water during those times.
Does this explanation help?
Be aware that electric tankless water heaters draw a huge amount of electricity--usually 120 amps or more. Older electrical services and panels may not be able to handle that load. They are definitely not appropriate for an off-grid home.