[RE-wrenches] On Demand Heaters for SDHW3

[Dan Fink]

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;