[LMB] OT: akicotl: water heaters?
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
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