[Greenbuilding] Opinions on electric tankless HW heaters?

Wed Apr 20 13:36:53 CDT 2011

I realize I did not clarify when I originally asked this question; that the clients in particular will not be living at the home full time. Between a second home in another state, and rigorous travel schedules, there is nothing "typical" about their potential use. The could quite possibly reside there with an additional family member or two at the same time, but likely in small doses.

To me; proper green design is about balancing various "best practiced" solutions. I guess the real question is: does the infrequent usage of an electric on-demand ever outweigh the need to keep water hot all the time? These are not clients who would remember to turn down the water heater, either. There may not be a "right" answer here. I certainly won't recommend this solution if it doesn't mutually benefit the clients and the planet.

Thanks,

Matt

On Apr 20, 2011, at 2:04 PM, Frank Tettemer <frank at livingsol.com> wrote:

> Hi All,
> 
> I can't vouch for Nick's idea that they only manufacture 13KW tank-less hot water heaters.  I think that the manufacturers would certainly provide electric tank-less heaters of all electrical load sizes, simply because there would be a demand for lighter-duty models, and Somebody is going to fill that market.  However,
> 
> That doesn't mean that a light-weight tank-less heater would provide a satisfactory supply of hot water.  And certainly anyone who has traveled South of the border, to various Carribean countries has experienced those light-duty electric shower heaters, plugged into an overhead electrical recepticle, just out of reach of the shower curtain.  (I'm not promoting these models for US or Can. use, however.)
> 
> What I do think is entirely wrong,
> is the idea that an electric hot water heater, of any make or model, could possibly be considered environmentally friendly.  It's just way too big of a stretch in reality.
> 
> Consider that a typical household of four would probably spend about $30 to $40 per month on heating hot water.  Either system, tank-less or tank.
> This is equal to about 400 Kwh, at the household's electrical meter base.
> This is also equal to about 1,300 Kwh of comparable fuel, being burnt at the coal plant, or nuked at the nuke plant.
> (As we know, the accumulated losses, from conversion of fuel to heat, conversion of heat to steam, conversion of steam to rotary motion, conversion of motion to electrical current, and line losses from transmission all add up to a factor of about 3.25 to 1.  This is a phenomena that is hard to accept, but even more impossible to ignore, while designing appropriate technologies in an energy efficient home.
> 
> Yes, Carmine, if we only look at the almighty dollar, and compare costs of various methods of heating domestic hot water, or heating hot water for distribution into household heating, the electric devices all end up costing less to purchase and to operate, in the initial assessment.
> 
> Giving regard to overall embodied energy of construction of the domestic hot water system, and associated energy of electrical production and transmission over a decade or two, however, the question arises as to how this all pans out over the coming decade or two.  Looking at a comparison of economics, via using the dollar as the unit of measure is way too short-sighted. It is misleading and hides the truth.
> 
> In my humble opinion, and in my home design practice, I have not specified any greater electrical use in a home that can be produced near to the location of the home.  As well, the PV array and/or wind turbine associated with the home's electrical production really must be capped at a small enough investment, (both dollars and embodied energy), that this system is also not a burden to the planet.  In other words, designing a 10KW PV system, plus a 10Kw wind turbine, for one single household, is to me a pathetically privileged idea, and un-necessary exhibition of wealth, and simply represents a too large footprint.  I have built many homes over the years, on of off grid, that operate on 3 to 5 Kwh per day, total electrical loads, simply to avoid the burden to the grid and to the planet in general.
> 
> If the average Canadian household uses 29 to 32 Kwh per day, then a home that uses only 5 Kwh per day is living more lightly.  And this difference, when converted to fuel consumption for the electricity used, represents over 2,000 units of fuel equivalency.
> This represents a savings upon the grid, and lightens it's load.
> 
> Nearly any other fuel will have a lighter impact than electricity for hot water.  And I'm not even taking nuke meltdowns, like in Japan, into the equation.  If we add that level of environmental toxicity to the balance sheet, avoiding electrical on-demand hot water heaters is a no brainer.
> 
> If we are serious about discussing economic and environmental waste, let's first consider simply living with less expectations, way less over-all consumption of all goods, accepting and surrendering to the uncomfortable fact that this planet cannot support our North American "needs" any longer, without these "needs" being clearly labeled as privilege and greed.
> 
> I believe that it is misleading people with advice that switching from one fossil fuel to another is going to "improve" the environment.  There is no "better" fossil fuel, just as there is no better way to continue to consume goods at the rate of most middle class households.
> 
> Our best fuel is a leap of faith around finding that living with way less is way better.
> 
> Frank Tettemer
> 
> Frank Tettemer
> Living Sol ~ Building and Design
> www.livingsol.com
> 613 756 3884
> 
> .............................................................................................................................................
> Nick: Please stop misleading people with your erroneous advice. We all know your prejudice against both tank-less heaters & tank-less drain water heat recovery systems that can deliver Energy Factors well above that offered by the kinds of water heaters you promote.
> Carmine
> gfxechnology.com
> 
> ------------------------------------------------------------------------
> From: npyner at tig.com.au
> To: greenbuilding at lists.bioenergylists.org
> Date: Tue, 19 Apr 2011 09:37:24 +1000
> Subject: Re: [Greenbuilding] Opinions on electric tankless HW heaters?
> 
> Instant electric is usually the last choice on economic and environmental grounds.
> I doubt that Rheem would make them. Another manufacturer that does is Stiebel Eltron. They have some pretty sophisticated models but they are expensive and probably no more efficient than their simpler ones.
> Even a small instant electric will take about 13kW, so retrofitting one may call for some expensive wiring.
> 
> Nick Pyner
> 
> Dee Why   NSW
> -----Original Message-----
> *On Behalf Of *Matt
> 
> I have clients who might be ideal candidates for a tankless hw heater. They don't have natural gas in their home. I have installed gas tankless, but don't have any experience with electric tankless heaters. I will need to size one for a family of two to four.
> 
> Any opinions out there? Bosch? Rinnai? Rheem?...
> 
> -- 
> 
> 
> 
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