In the desert Southwest we tend to use wells for water supply, and
our water is often quite hard. While we don't do plumbing or DHW, we
are often asked to advise on other aspects of home systems. We
advise generally against tankless heaters because of our
groundwater. The minerals leach out when the water is heated - like
the film that slowly forms inside a teapot and is cleaned out with
vinegar. Tankless heaters rely on small passages for maximum surface
area to heat water quickly. The passages slowly clog with mineral
buildup. So they end up costing enough in cleaning, maintenance and
repair costs to negate any advantage due to their higher thermal
efficiency.
Bottom line - their value depends on the characteristics of the
water you run through them.
On 9/16/2010 9:00 PM, Dan Fink wrote:
I
work exclusively with smaller off-grid systems in remote areas. So
on-demand heaters are the only thing I deal with....many of these
systems are not occupied for lengths of time (fishing and hunting
tourist lodges, summer cabins, etc.). A tank heater doesn't make
sense in these applications, especially if run only on propane (no
solar DHW).
Almost all my troubleshooting calls have been from clients
self-installing new fixtures that don't allow enough flow for the
heater to turn on....or clogged pump intakes (from using river
water and rainwater) doing the same. A leaky pressure pump (it
froze up a bit last winter, but she's still a-workin', but the
heater don't, what's wrong?) will do the same too--hot water
until the pressure tank runs out, and not enough pump to keep up
because of the leaks.
Anyway, there are facets of on-demand that are PITA. But it's the
way of the backwoods, unless there is also solar DHW....then a
tank works.
DAN FINK
Buckville Energy Consulting
Darryl Thayer wrote:
> Hi all
> I have done several On Demand Heaters with SDHW, typically
the SDHW provides 100% all summer (7-8 months) and then falls
short in the winter. I have never done a On Demand Heater that
has made the customer happy. They all have complained about
'chase the temperature' because there is a range in which the
heater will want to fire or not fire, and at some time they will
be in that temperature range. then the unit will fire and not
fire and the temperature changes at the fixture. They complain.
I get complaints even when the On Demand Heater is installed by
others. I tell customers, that the system will work with the
standard design, but if they want to install a On Demand, I am out
of the loop. Darry;
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