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Solar + Tankless Gas for DHW: A good combination?

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Posted by Steve on May 2, 2006, 2:39 am
I've been considering a solar domestic hot water system (DHW).  There isn't
enough space in our house to easily place solar tank with a heat exchanger
to preheat our existing gas water heater.

It does however look like there would be enough room to put in a solor tank
as a pre-heater to a tankless (continuous flow) gas water heater .  Does
this sound like a good combination, or am I missing something.

Thanks in advance,

Posted by SJC on May 2, 2006, 2:52 am

  I don't see a problem with this. There is also the option of going =
a thermosiphon design which puts the tank up by the collector and inline
with the water main, as a preheater.

Posted by Gary on May 2, 2006, 3:43 am
 Steve wrote:

I believe that tankless heaters will work with solar as you describe.

You need to get a tankless heater that can modulate its flame to only add as
much heat as is needed to heat your water from the temperature in your preheat
tank up to the hot water temp you want.  Not all of the tankless water heaters
have this feature.



"Build It Yourself" Solar Projects

Posted by SJC on May 3, 2006, 2:34 pm

  One thought I had was the temperature rise through the tankless heater =
at a
given flow rate. If you are taking a shower and the solar tank is low =
does the tankless raise the temperature enough. Another consideration is =
a temper
valve, so that the water from the solar tank does not come out too hot, =
but a differential
controller should be able to keep the solar tank below the maximum =
  On the cautious side, a tank sitting around at say 90F could have =
bacterial where a
tank sitting at 140F would not. Does the tankless heat the water up high =
enough for
long enough to kill any bacteria. This may not be a major concern with =
well water
but water sitting at just the "right" temperature for certain bacteria =
might be a

Posted by dold on May 3, 2006, 8:16 pm
I am thinking of this as well, but the good tankless heaters are very
expensive.  Also be aware that they require a very good supply of gas.  A
friend had one poorly installed, and in the morning there wasn't enough gas
flow available to the heater if the house heater was also on.  Adding a
separate pipe run just for the heater made it work fine.

Clarence A Dold - Hidden Valley Lake, CA, USA  GPS: 38.8,-122.5

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