Tankless Water Heater Scaling etc. [RE-wrenches]

Matt Tritt solarone at charter.net
Thu Oct 28 09:18:26 PDT 2004


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  Bill,

  I don't think that this is completely correct.

  A properly built tankless heater like the Aquastar has very thin wall heat 
exchangers that flex considerably during cold-hot cycling. Flexing causes 
the acumulated calcium carbonate, which is not flexible, to flake off and 
pass through the system without affecting performance (with the exception of 
faucet aeration screens getting clogged-up).

  I've had a Myson in service here since '90 that has only required service 
once, and that was on the proportional gas contol valve. The problem with it 
was precisely because of the corrosive nature of softened water that often 
attacks brass parts in plumbing systems and, more frequently, thin wall 
copper pipe.

  If you are in a really hard water area you might try a clamp-on magnet on 
the cold water inlet to the water heater to prevent  calcium build-up. 
Believe it or not, this method is universally used by boiler companies and 
maintenance people all over the world with success. Yes, I can hear the 
collective groans, but it actually does work.

  Matt T
  ----- Original Message ----- 
  From: "Bill Loesch, Saint Louis Solar" <bill_loesch at compuserve.com>
  To: <RE-wrenches at topica.com>
  Sent: Thursday, October 28, 2004 4:41 AM
  Subject: Tankless Water Heater Scaling etc. [RE-wrenches]




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  Fellow Wrenches:

  Scaling is a function of water "hardness" and water temperature.

  Heat hard water and you precipitate the suspended minerals. Heat hard 
water
  a lot and you precipitate a lot of minerals. Scaling happens in tanks just
  the same as in tankless. The gas hot water tank control continues to
  function (albeit with less sensitivity) long past the time the tankless
  control _requires_ service.

  I am unaware of any good reason to heat the tankless hot water above what
  you would utilize at the tap.

  Both the tank and the tankless manufacturers _recommend_ maintenance. The
  tankless unit (in a hard water area) will require maintenance.

  Water conditioning is the solution to hard water and scaling. This can 
take
  the form of a water softener or a "scale inhibitor". Water softeners
  benefit all downstream plumbing and offer user benefits. Scale inhibitors,
  installed upstream of the water heater, in the form of a cartridge filter
  or similar, also benefit only downstream plumbing. Obviously, there is
  ongoing maintenance (and cost) with either the softener or the inhibitor.
  Hopefully less than descaling. Cuno manufactures more than one style of
  scale inhibitor under the Aqua-Pure label (and perhaps others).

  Rinnai in their latest installation instructions recommends adding hose
  bibs inboard of the full port ball valves during the heater installation.
  This is solely to facilitate subsequent descaling of the heater.This also
  provides an opportunity for Rannai to sell a matching cover for the
  additional plumbing.

  Regarding the minimum flow, no tankless will provide a trickle of hot
  water. If you must have a trickle you must have a tank. In the case of the
  frugal hot water user below, she must be instructed to open the tap to at
  least the minimum flow rate (0.5 gallon per minute or higher with larger
  models) to activate the heater. A legitimate frugal dishwasher would not 
be
  using running water to wash the dishes anyway, she should be using a
  dishpan. It is a matter of education or lifestyle change and should be
  discussed _before_ the installation as well as a number of other issues.

  The one hundred watt idle draw was probably one of the electric freeze
  protection heaters actuating inappropriately. Some of the tankless
  manufacturers are recommending mounting these tankless units, often in a
  ganged configuration, on commercial rooftops in freezing climates. The
  internal electric heaters only protect the heater itself, not the
  connecting piping. Obviously, if the power fails during a freezing
  condition there is no protection whatsoever. IMHO, another not so good
  idea.

  Bill Loesch
  bill_loesch at compuserve.com
  tel / fax 314 631 1094
  Solar 1 - Saint Louis Solar
  www.solar1online.com
  9905 Vasel Drive
  St Louis MO 63123-4321



  Ray Walters said:
  > Hi Scott;

  >We've seen this scaling problem here with Aquastars. I quit selling them
  for the most part,
  >because of the scaling problem and the fact that they  don't fire at low
  flow rates. Nothing like
  >selling a good customer a Staber  washer and an Aquastar and then the
  Staber doesn't use enough
  >water to get  the Aquastar to fire! Or the frugal old lady on a rain 
catch
  cistern that  washes
  >dishes with a quart/ minute and it won't fire either. I recently had a
  customer with a "Rannai"
  >hotwater heater. It had an almost  100 watt draw while in standby!  It
  must have had a glowbar or
  >something in  there. It also was not mod sine friendly. It was replaced
  with an Aquastar,  since
  >there wasn't space for a regular hotwater heater.

  >Ray

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