[RE-wrenches] On demand WH

[Bill Loesch]

Hi Bill, et al,

There are two major categories of tankless water heaters-natural draft 
(which work very similar in control aspect to a conventional tank i.e.. 
no electric required, some form of pilot light) and power vented (all 
power vented machines have need for at least a fan, most a computer with 
some form of display included - if your own body is incapable of telling 
you if the water is sufficiently hot).

Of the Big Five (major players in the tankless market) all manufacture 
one or more models of power vented tankless. Today, only Bosch markets a 
natural draft tankless. Bosch offers more than one model of natural 
draft tankless, standing pilot and intermittent pilot. If you like 
simple, trouble free, and low life cycle cost, you have but one choice.

 
http://www.bosch-climate.us/files/201304181918370.520PN_English_06.2011.pdf

What must be properly addressed with _any_ tankless is intake and 
exhaust venting, gas line sizing, and water quality. Since this isn't a 
tank, the pilot flame does almost nothing in terms of freeze prevention.

Some manufacturers state flow rate for their heaters without also 
providing temp rise. Flow rate without temp rise is meaningless. The 
above is a 117,000 BTU/h machine. Sometimes winter ground water 
temperatures are significantly colder than summertime temps. If you want 
hot water in the winter, too, make sure you use the appropriate temp 
rise. Hardness is the biggest issue with water quality, if you scale the 
heat exchanger you won't get the performance advertised. If you have 
hard water, a water softener or descaling _as required_ is necessary.

I am a big fan of tankless and have been since '89 when I was first 
introduced to them as a user. Today, I install and troubleshoot all five 
major manufacturers. Co-located with the load, tankless provides you not 
only endless hot water but also instant hot water.

Good luck,

Bill Loesch
Solar 1 - Saint Louis Solar
314 631 1094


On Sat, Sep 28, 2013 at 10:19 PM, frenergy wrote:

> Off-grid Wrenches,
>
>         I'm working on a load sheet and am having a hard time finding 
> standby and while firing electrical usage for a propane-fired on 
> demand water heater.  Do they some/all have standing pilots, glow 
> bars, something else?  I'm guessing the standby power needs are very 
> low but we all know how even 10-15 watts adds up over 24 hrs when 
> you're off-grid.
>
>         If any body has some actual numbers rather than just pdf.specs 
> (though manus specs might help some), I would be most grateful. 
> Thanks in advance.
>
> Bill
> Feather River Solar Electric
>
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