Tankless ... again

CEFreemanOctober 10, 2011

Hi all!

I would like to know if anyone has info on the most efficient electric tankless water heater.

I don't need all the warnings/data/info/blahblahblah about gas vs. electric because I know all that. It's irrelevent to my situation.

I am wondering about the difference between manufacturers. I also am not sure WHO the manufacturers are, so any recommendations would be great.

Thanks,

Christine

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ronaka

Your issue in comparing heaters is that Energy Star does not rate electric tankless hot water heaters to my knowledge. The reason may be that essentially all products should be approaching 100% efficient. All heat goes into the water except for some very small electrical resistance losses in the wiring outside the heater, and of course heat loss in the warmed water -- which again is going to be very small.

I see Bosch claim 90% at the link below, but I'm not sure why they are not saying 99%. There are very limited places where you can have losses. Gas, propane, and oil heaters of course lose heat with the exhaust gases, so they have various efficiency ratings based on how well they recover exhaust heat. Not the situation at all with electric tankless heaters.

This may be in your "blablabla..." category, but your first check should be the electrical service to your house, and whether or not it can handle the current draw of a tankless electric. In more northern climates you probably need a 200 amp service. Many houses only have 100 amp, and some older ones even less. It may require new power lines run into your house. I worked for a electric utility company for 35 years before I retired.

Here is a link that might be useful: Bosch Electric Tankless

    Bookmark   October 10, 2011 at 11:52AM
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CEFreeman

Yes, the lack of Energy Star rating was why I was asking for (personal experience and) recommendations.

The blah/blah is the inefficiency of an electric vs. gas.

However, I live alone. I do dishes and laundry in cold water. I need this hot water only for showering and my bathroom sink, which is 70' from the (solar) water heater. If I let the water run for 10 minutes, it's hot and lovely. However, even on a well, that's a lot of waste. Hence the consideration of a tankless.

I have 32 solar panels and in this bathroom, new wiring. As I am still under reconstruction, I can have things wired any what I want.

The link you sent to me is great. I love Bosch products & the size of this is great. I have 18" wide to play with.

Thanks!
Christine

    Bookmark   October 10, 2011 at 12:07PM
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ronaka

Since you have a solar hot water heater, you may want to consider a recirculation system, instead of a tankless heater. See link below. I think it would be much cheaper to buy, and would require far less power. Installation cost will depend on ability to run the extra water lines back to the solar tank.

If you go tankless electric, you should look for a point of use type that could be installed close to where you use it. Those Bosch ones I believe are intended for a whole house. However, tankless means you have to add heat at the same rate as you use it, so they still have to be high power input just to keep up to a single shower. I wouldn't worry about efficiency as I said earlier they should all be about the same and close to 100%. Base decision on cost, features, and availability.

Here is a link that might be useful: Armstrong Recirculation System

    Bookmark   October 10, 2011 at 12:58PM
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jakethewonderdog

Christine,

All electric tankless heaters are about 100% efficient.
A well insulated Tank style electric heater is about 4% less efficient (which is why electric tankless almost never makes sense)

Electric tankless require huge amounts of current - if you had any thought of powering the the tankless from a PV cell, forget it.

    Bookmark   October 10, 2011 at 3:11PM
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justalurker

You will still wait for the hot water to travel 70 feet to where you want it regardless of the device heating the water.

Changing to a tankless heater will not change that.

You might consider this.... http://www.chilipepperapp.com/cwrcs.htm

Chilipepper has an on demad model that is controlled with a button. You want hot water, you push the button, the pump pumps, and hot water travels the 70 feet to your sink,

I have a temperature controlled version of this from another manufacturer and it has worked nicely for 8+ years. I used to have to wait almost 2 minutes for hot water and now, it's pretty much right there when we want it.

Water bill went down and electric bill didn't seem to increase.

    Bookmark   October 10, 2011 at 3:55PM
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CEFreeman

I wasn't thinking of powering a tankless from a PV cell, nor 32 of them.

My point was that I have a $7.00 power bill in July, so some extra energy usage isn't going to freak me out. With my showering habits, living alone, it's not a big deal.

I would install any heater (point of use sounding most sensible) under the counter I haven't built yet, right next to the shower and sink where I would be using it. So changing does make more sense.

I still don't want to waste 5-10 minutes worth of water getting it from my pump & current system to the bathroom.

Thank you all for your opinions & I'll check out the recommendations.

Christine

    Bookmark   October 11, 2011 at 9:47AM
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jakethewonderdog

The under-counter point of use can make a lot of sense, as long as you are very hip to the temp rise/gpm /current issue. All electric tankless at the same voltage will have the same relationship between current and heat rise for a given gpm.

You can hook in series with central water heater so that the central heater takes over after the hot water reaches the tankless.

Again, I don't think it much matters what brand you use since they are all similarly efficient. Look at other issues such as durability and parts availability.

    Bookmark   October 11, 2011 at 1:52PM
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ronaka

"I still don't want to waste 5-10 minutes worth of water getting it from my pump & current system to the bathroom."
------

Check out the recirculation system I posted information on, as it will solve this problem. It simply recirculates the water back to the heater inlet. The power to do this is very small and the pump will run off any house plug in. Not so with a tankless heater. Even a point of use type will want big amps if you want it to keep up to a normal shower usage.

There are various ways to run a recirculation system. One is simply manual. 5 minutes or probably less before you want to shower, you turn it on. Other options are to have it run all the time (but probably a waste of power), or run based on a timer for usual use periods. They will even turn off and on automatically during the timed on period based on temperature.

Armstrong is one system that offers all these options, but I'm sure there are many others on the market.

    Bookmark   October 11, 2011 at 4:09PM
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