[LMB] OT: akicotl: water heaters?

David McMillan skyefire at skyefire.org
Mon Dec 4 02:18:36 GMT 2006


Becca Price wrote:
> I mostly lurk here, but enjoy all the discussions. Now I'd like
> to take advantage of the amazing fund of knowledge here, and ask
> a very ot question. We're looking at installing an on-demand
> water heater, and I haven't the first idea where to start
> looking at them, or what to look for. Does anyone have one of
> these, and can give me some pointers?

	General pointers:  the critical specs are temperature increase vs flow 
rate.  Basically, in any on-demand water heater (generally called 
"tankless" water heaters, particularly on EBay), the water only spends a 
certain amount of time inside the heater before it leaves.  The faster 
the water passes through the heater, the less time it has to heat. 
Hence, a tankless heater with a given power rating may heat the water 
passing through by 40F at a rate of 2.5 Gallons Per Minute, but only 20F 
at 5GPM.  Basically, a given heater will take the input water and 
increase its temp by X degrees for a given flow rate, so if the heater 
is only rated to provide 40F, feeding it 40F water will result in only 
80F output water -- not necessarily enough if you want to kill germs in 
a dishwashing machine, say.
	Obviously, the stronger the heater, the more expensive it is.  There 
are smaller tankless heaters on EBay, attractively cheap, that are only 
intended to supply one low-flow shower head, and wouldn't give much heat 
to a larger pipe.
	Some models will just add what heat they can to the input water 
regardless of output temp.  Others include an upper-limit thermostat, 
which will keep the output water below a certain temp even if the input 
water is warmer than usual.
	If going electric, check the Volt/Amp specs -- some units can be wired 
in multiple ways, others only one way.  Make sure the electric circuit 
you're using can support the heater -- 220VAC 3-Phase units are rare, 
but buying one for a household application where on 1-phase 220 is 
available would be an unfortunate waste of money.  Watch the different 
amp draws as well -- plugging a multi-voltage unit into 110VAC instead 
of 220VAC might work perfectly well, but will draw about twice the 
amperage for the same power output.
	I'm currently obtaining a relatively low-flow 220VAC single-phase unit 
to associate to my father's power washer.  He uses it to wash down his 
honey equipment, but needs ~120F water to do the job, and getting hot 
enough water through the long garden hose out to washdown area is a 
pain.  I'm hoping to be able to generate 120F water on-site from 
room-temp water.




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