[RE-wrenches] On Demand Heaters for SDHW3

[Bill Loesch]

Allan,

Everything you say is spot on. Scale is the _mortal_ enemy of all tankless water heaters. Hopefully you change the air cleaner on your vehicles more often in the dusty desert climate than you would in a less dusty climate. Same principle. You accept the need to change out the tank when if fills with scale, the tankless offers you the option to maintain rather than replace. If the water quality is that bad, your clothes washer and dishwasher and every hot water valve are also suffering the effects of scale and providing you with reduced appliance and fixture life. 

If the maintenance chore is an issue, have you considered a water softener/water conditioner/etc. If the cost is an issue, descaling a tankless is only slightly more involved than circulating the descaling fluid in the coffee machine.

I like to look at the places in the world where others pay a premium for fuel and take their lead in energy related matters. Tankless is a clear winner using this criteria.

Respectfully,

Bill Loesch
Solar 1 - Saint Louis Solar

  ----- Original Message ----- 
  From: Allan Sindelar 
  To: Dan Fink ; RE-wrenches 
  Sent: Thursday, September 16, 2010 11:52 PM
  Subject: Re: [RE-wrenches] On Demand Heaters for SDHW3


  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.


  Allan Sindelar
  Allan at positiveenergysolar.com
  NABCEP Certified Photovoltaic Installer
  EE98J Journeyman Electrician
  Positive Energy, Inc.
  3201 Calle Marie
  Santa Fe, New Mexico 87507
  505 424-1112
  www.positiveenergysolar.com


  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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