DIYbanter - View Single Post

wrote:
Given that they are all electric, it would probably be cost prohibitive
as they would need multiple units to achieve a reasonable flow at the
temperature (city water temp vs. outlet temp) rise thye are likely to
experience. If they get a Nat Gas or Propane line then a single unit
might make sense (if they went with one of the largest available).

Nevertheless, to appropriately assess the situation you need some more
facts: Specifically you need to know what they believe their maximum
simultaneous hot water usage might be. For example, if they are
expecting to be able to take 2 showers, run the DW, and wash clothes
simulataneously then you get a very different answer than if they are
willing to live with never using more than 1 source of hot water at a
time. Figure on 2.5 GPM per outlet while in use and you'll quickly
come to a total GPM that the tankless unit needs to produce.

From there you can simply assess the various manufacturers specs for an
approx. 70-80 degree temp rise (depending on water inlet temp and how
hot they like their water) and see whether the unit can provide the
necessary volume of hot water.

Doug

So with high 60s to mid 70s inlet water temp and a rise of 45F, the
large units (185K to 190K BTU input) will easily supply 3 simultaneous
use, and hot water recovery via GFX and/or geothermal heat pump could
make this even higher!!! Course, geothermal heat pump only assists in
this process UNLESS you get their option to produce all hot water (i.e
run heat pump JUST to generate DHW thru a heat exchanger inside a
dedicated DHW tank)