Demand heater for SHW backup [RE-wrenches]

[Allan Sindelar]

For several years I was a de facto student of solar thermal resource Bristol
Stickney, who had been director of research for the New Mexico Solar Energy
Association back in the early 1980s, and made his living keeping DHW systems
going after the bottom fell out of the industry under Reagan. He taught me
that from this experience he stopped using or recommending tankless water
heaters in our region. He explained that by design, a tankless heater uses
small water passages to maximize surface area for burner heat transfer for
fast temperature rise. In our area (and probably many others as well) our
water is hard, and heating water causes the dissolved minerals to leach out
and gather as scale on the heat exchanger surfaces. The result is clogged
passages and frequent maintenance for scale removal. Add to that their
inherent complexity, and he determined that the gain in efficiency wasn't
worth the ongoing cost of maintenance and repairs. I have counseled that
advice to many in the years since, although we don't do thermal work. His
company (www.cedarmountainsolar.com) uses high-efficiency sealed-combustion
boilers pretty much exclusively now.

My $.02.
Allan at Positive Energy

----- Original Message ----- 
From: "Travis Creswell" <tcreswell at ozarkenergyservices.com>
>
> We've used tanked propane water heaters in low load radiant in floor
> applications and domestic water heating. They were the power vent style
> models with an electronically controlled igniter so no standing pilot
light.
> Plus a damper built into the power vent that automatically closed when the
> burner wasn't firing which would help with draft losses and tighten up the
> building envelope.  These models are readily available locally and
> reasonably priced (less then $600 the last time we bought one).  Energy
> factor on these units is in the low to upper 60's. Not the greatest but
they
> do everything else so well.
>
> We are not fans of tank less water heaters.  We've had too many
reliability
> and customer usage problems with them.  I'm totally confident that if you
> looked at the total 10 or 20 year cost of ownership of a tankless unit vs.
> standard unit the tankless would loose.
>


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